The measurement of black hole spin is considered one of the key problems in relativistic astrophysics. Existing methods, such as continuum fitting, X-ray reflection spectroscopy, and quasi-periodic oscillation analysis, suffer from limitations in accuracy, interpretability, and scalability. In this work, a hybrid approach is proposed in which theoretical models based on the Teukolsky formalism are integrated with Physics-Informed Neural Networks (PINNs). A PINN model is developed to solve the linearized spin problem in the scalar case, with physical constraints directly embedded into the training process. Annotated data are not required; instead, the model is trained using the differential operator and boundary conditions as supervision. It is demonstrated that the PINN converges reliably, with residual loss values below 10 and a root mean squared error (RMSE) on the order of $10^{-7}$. Benchmarking results indicate that the proposed method outperforms both classical and data-driven machine learning approaches in terms of AUC and sensitivity, while also exhibiting superior interpretability, generalizability, and adherence to physical principles, with moderate computational cost. Potential extensions include integration with general relativistic magnetohydrodynamics (GRMHD) solvers and application to real observational data. These findings support the viability of physics-based machine learning as a robust framework for accurate and interpretable black hole spin estimation.

We present high-resolution ALMA [CII] 158 micron observations and JWST/NIRCam+MIRI imaging of MAMBO-9, a pair of optically-dark, dusty star-forming galaxies at $z=5.85$. MAMBO-9 is among the most massive, gas-rich, and actively star-forming galaxies at this epoch, when the Universe was less than 1 Gyr old. The new, 400 pc-resolution [CII] observations reveal velocity gradients in both objects; we estimate dynamical masses and find a relative mass ratio of 1:5. The kinematics of both objects suggest both rotation and strong tidal interaction, suggesting that the pair has already experienced a close encounter. Indeed, the new JWST imaging reveals a continuous bridge of moderately dust-obscured material between the two. We perform spatially-resolved SED fitting using the high-resolution ALMA+JWST imaging, finding that the majority of recent star-formation is concentrated in extremely obscured ($A_V > 10$) clouds, while the majority of rest-optical light (stellar continuum and H$\alpha$ emission) is emergent from moderate-to-highly obscured ($A_V\sim 1$-$5$) regions on the outskirts. Combining our new stellar and dynamical mass measurements with previous CO observations, we find that the mass budget of MAMBO-9 requires a CO-to-H$_2$ conversion factor ($\alpha_{\rm CO}$) of roughly unity, indicative of a highly metal-enriched ISM. Finally, we show that MAMBO-9 resides in a large overdensity spanning the PRIMER-COSMOS field, with 39 galaxies spectroscopically confirmed within $\sim 25$ cMpc. With a total baryonic mass $\sim 10^{11}\,M_\odot$, MAMBO-9 can be considered a prototype of massive galaxy formation and likely progenitor of the brightest cluster galaxies (BCGs) in the lower-redshift Universe.

We describe the second data release (DR2) of the FIRE-2 cosmological zoom-in simulations of galaxy formation, from the Feedback In Realistic Environments (FIRE) project, available at http://flathub.flatironinstitute.org/fire. DR2 includes all snapshots for most simulations, starting at z ~ 99, with all snapshot time spacings <~ 25 Myr. The Core suite -- comprising 14 Milky Way-mass galaxies, 5 SMC/LMC-mass galaxies, and 4 lower-mass galaxies -- includes 601 snapshots to z = 0. For the Core suite, we also release resimulations with physics variations: (1) dark-matter-only versions; (2) a modified ultraviolet background with later reionization at z = 7.8; (3) magnetohydrodynamics, anisotropic conduction, and viscosity in gas; and (4) a model for cosmic-ray injection, transport, and feedback (assuming a constant diffusion coefficient). The Massive Halo suite now includes 8 massive galaxies with 278 snapshots to z = 1. The High Redshift suite includes 34 simulations: in addition to the 22 simulations run to z = 5, we now include 12 additional simulations run to z = 7 and z = 9. Most simulations include catalogs of (sub)halos and galaxies at all available snapshots, and most Core simulations to z = 0 include full halo merger trees.

Asteroseismology, the study of stellar oscillations, provides high-precision measurements of masses and ages for red giants. Scaling relations are a powerful tool for measuring fundamental stellar parameters, and the derived radii are in good agreement with fundamental data for low-luminosity giants. However, for luminous red giant branch (RGB) stars, there are clear systematic offsets. In APOKASC-3, the third joint spectroscopic and asteroseismic catalog for evolved stars in the Kepler fields, we tied asteroseismic radii to a reference system based on Gaia astrometry by introducing correction factors. This work proposes an alternative formulation of the correction scheme, which substantially reduces the sensitivity of the results to the technique used to infer mean density from frequency spacings. Compared to APOKASC-3, our adjusted correction scheme also reduces fractional discrepancies in median masses and ages of lower RGB and upper RGB within the $\alpha$-rich population from $6.65\%$ to $1.72\%$ and from $-21.81\%$ to $-9.55\%$, respectively. For the $\alpha$-poor population, the corrected mass scale leads to an improved agreement between theory and observation of the surface carbon-to-nitrogen abundance ratio, a significant diagnostic of the first dredge-up.

We study the optical variability characteristics of Active Galactic Nuclei (AGN) from the Swift Burst Alert Telescope (BAT) AGN catalogue by utilising approximately five years of optical light curves from the Zwicky Transient Facility (ZTF) survey. We investigate dependencies of the long-term optical variability amplitudes and timescales on (i) supermassive black hole (SMBH) mass, luminosity, and Eddington ratio to explore the influence of accretion disk dynamics and radiative processes; (ii) X-ray properties, such as spectral photon indices and fluxes, to study the effect of high-energy emission mechanisms; and (iii) radio characteristics, such as integrated fluxes and radio loudness, which indicate jet activity. Our findings confirm a positive correlation between the variability time scale and both the SMBH mass and luminosity, suggesting that these physical parameters significantly impact the optical variability timescale. Conversely, no significant dependence is found between optical variability and X-ray properties, indicating that high-energy processes may not substantially influence long-term optical variability. Additionally, a weak anti-correlation between optical variability and radio parameters suggests that jet activity has a negligible effect on causing long-term AGN variability. These results support the hypothesis that long-term optical variability in AGN is primarily governed by thermal emission from the accretion disk. Further investigations with larger samples are essential to refine these correlations and develop robust physical models integrating black hole properties, accretion disk physics, and multi-wavelength radiative transfer.

The vast majority of young stars hosting planet-forming disks exist within clustered environments, like the Orion Nebula, implying that seemingly 'extreme' UV environments (10^4 G_0 and above) are not so atypical in the context of planet formation. Using thermo-chemical modeling, we explore how the temperature and chemistry within a protoplanetary disk around a T Tauri star is impacted by the surrounding UV environment. The disk becomes hotter due to heating by photodissociation of molecules, photoelectric heating, H_2, and atomic processes and as a result the area in which molecules exist in the ice-phase shrinks, being pushed both downward and inward. Beyond 1AU the chemistry changes most significantly in a UV-rich background; the atmosphere becomes more H2O, OH, and atomic-rich. Hydrocarbons, however, reside primarily well within 1AU of the disk, thus their abundance and distribution is not impacted by the UV field, up to a 10^6 G0. The products of photodissociation and photochemistry are formed deeper into the disk with increasing UV background field strength beyond 1AU, impacting the chemistry near the midplane. Effectively a 'reset' chemistry takes place, with an enhancement of atoms, simple molecules, and molecules in the gas-phase. Planets that form in highly irradiated regions will be exposed to a different chemical reservoir in the gas and ice-phases than that in an isolated disk, and the impact from the UV background should only be detectable in highly irradiated disks (~10^6 G_0).

The intense stellar irradiation of ultra-hot Jupiters results in some of the most extreme atmospheric environments in the planetary regime. On their daysides, temperatures can be sufficiently high for key atmospheric constituents to thermally dissociate into simpler molecular species and atoms. This dissociation drastically changes the atmospheric opacities and, in turn, critically alters the temperature structure, atmospheric dynamics, and day-night heat transport. To this date, however, simultaneous detections of the dissociating species and their thermally dissociation products in exoplanet atmospheres have remained rare. Here we present the simultaneous detections of H$_2$O and its thermally dissociation product OH on the dayside of the ultra-hot Jupiter WASP-121 b based on high-resolution emission spectroscopy with the recently commissioned Near InfraRed Planet Searcher (NIRPS). We retrieve a photospheric abundance ratio of log$_{10}$(OH/H$_2$O) $= -0.15\pm{0.20}$ indicating that there is about as much OH as H$_2$O at photospheric pressures, which confirms predictions from chemical equilibrium models. We compare the dissociation on WASP-121 b with other ultra-hot Jupiters and show that a trend in agreement with equilibrium models arises. We also discuss an apparent velocity shift of $4.79^{+0.93}_{-0.97} $km s$^{-1}$ in the H$_2$O signal, which is not reproduced by current global circulation models. Finally, in addition to H$_2$O and OH, the NIRPS data reveal evidence of Fe and Mg, from which we infer a Fe/Mg ratio consistent with the solar and host star ratios. Our results demonstrate that NIRPS can be an excellent instrument to obtain simultaneous measurements of refractory and volatile molecular species, paving the way for many future studies on the atmospheric composition, chemistry, and the formation history of close-in exoplanets.

We argue that star formation in the disks of low-surface-brightness (LSB) galaxies shares a similar nature with that occurring in the far outer regions of normal-brightness spiral galaxies, such as those with the extended ultraviolet (XUV) disks. In both cases, stars are born in gravitationally stable disks with an extremely low average gas density (on kiloparsec scales), and the efficiency of this process depends on a disk brightness in a similar way. Processes which can stimulate star formation under these conditions are shortly discussed.

We present new photometric observations of the core-collapse supernova SN 2023ixf occurred in M101, taken with the RC80 and BRC80 robotic telescopes in Hungary. The initial nickel mass from the late-phase bolometric light curve extending up to 400 days after explosion, is inferred as $M_{\rm Ni} = 0.046 \pm 0.007$ M$_\odot$. The comparison of the bolometric light curve with models from hydrodynamical simulations as well as semi-analytic radiative diffusion codes reveals a relatively low-mass ejecta of $M_{\rm ej} \lesssim 9$ M$_\odot$, contrary to SN~2017eaw, another H-rich core-collapse event, which had $M_{\rm ej} \gtrsim 15$ M$_\odot$.

Gravitational lensing of short astrophysical transients provides a uniquely direct avenue for searching for primordial black holes (PBHs) across a vast range of masses. While past search efforts have focused on particular source classes-such as fast radio bursts (FRBs) and gamma-ray burst spikes-no systematic, multi-wavelength survey has compared their relative potential for PBH discovery. We present here a broad assessment of transient lensing search opportunities, spanning more than twenty decades in photon frequency and over twelve orders of magnitude in PBH mass. For each class, we determine the accessible PBH mass window by accounting for wave-optics suppression and time-delay resolution limits, and we estimate potential sensitivities to the PBH abundance using representative event rates, distances, and optical depths. Our survey includes low-frequency radio events (FRBs, pulsar giant pulses, planetary cyclotron bursts), optical/infrared signals, and high-energy phenomena (gamma-ray burst spikes, fast X-ray transients, TeV blazar flares). We synthesize these results in a unified mass-abundance diagram and comprehensive tables summarizing both physical reach and observational requirements. This work serves as a roadmap for optimizing future multi-wavelength lensing searches, guiding the design of instruments and strategies to explore the PBH dark matter hypothesis across its remaining viable parameter space.

Fast (V$_{\rm CME}$>1000${\rm \,km\,s^{-1}}$) coronal mass ejections (CMEs) capable of accelerating protons beyond 300MeV are thought to trigger hours-long sustained $\gamma$-ray emission (SGRE) after the impulsive flare phase. Meanwhile, CME-CME interactions can cause enhanced proton acceleration, increasing the fluxes of solar energetic particles. This study explores the role of fast CME interactions in SGRE production during CME clusters, which we define as a series of CMEs linked to >C-class flares with waiting times <$\,$1$\,$day from the same active region (AR). We focus on clusters in major CME-productive ARs (major ARs), by defining a major AR as one that produced >$\,$1 CME-associated major (>M-class) flare. The study identified 76 major ARs between 2011 and 2019, of which 12 produced all SGRE events. SGRE-producing ARs exhibit higher median values for the speed of their fastest CMEs (2013 vs. 775${\rm \,km\,s^{-1}}$) and the class of their strongest flares (X1.8 vs. M5.8), compared to SGRE-lacking ARs. They also produced relatively faster CMEs (median speed: 1418 vs. 1206.5${\rm \,km\,s^{-1}}$), with the SGRE-associated CMEs occurring during periods of higher CME rates than typical fast CME epochs. Twelve of 22 (54.5%) SGRE events and 5 of 7 (71.4%) long-duration (>$10\,$h) SGRE events occurred during CME clusters, with high chances of CME-CME interactions. A case study on very active major ARs showed that all SGRE-associated CMEs with V$_{\rm CME}\lesssim$ 2000${\rm \,km\,s^{-1}}$ underwent CME-CME interactions within 10$\,$R$_\odot$, while SGRE-associated CMEs faster than 3000${\rm \,km\,s^{-1}}$ did not undergo interactions.

We present spatially resolved maps of morphology, kinematics, and energetics of warm ionized gas in six powerful radio galaxies at z=3.5-4, using JWST/NIRSpec IFU to quantify jet-driven feedback in the early universe. All sources exhibit broad [OIII] emission-line profiles with W80 (line width) values of 950-2500 km/s across $\sim$10s of kpc, signifying large-scale outflows. The outflowing nebulae are preferentially aligned with the radio jet axis, suggesting jet-driven origin. On average, the regions with the broadest lines and highest velocities are co-spatial with radio lobes or cores, and exhibit the strongest kinetic power. Ionized gas masses associated with the outflows span 1 to 8 $\times 10^{9} \ M_\odot$, with total mass outflow rates of 80-950 Msun/yr and kinetic powers between 10^{43.2} and 10^{45.0} erg/s. The outflow kinetic power corresponds to 0.15%-2% of the AGN bolometric luminosity, sufficient to impact galaxy evolution. However, only $\lesssim 1$\% of the jet mechanical energy couples to the warm ionized gas via outflows, consistent with predictions from hydrodynamic simulations. A large fraction of the jet energy may instead reside in shock-heated hot gas, supported by X-ray detection, or used to thermalize the gas and produce the observed emission-line nebulae. Our results demonstrate that radio jets in massive, gas-rich systems at high-redshift can inject significant kinetic and thermal energy to the surroundings, providing direct evidence for jet-driven feedback operating during the peak epoch of galaxy formation.

Globular clusters (GCs) offer a unique environment for discovering and studying millisecond pulsars. In this paper, we present a multi-epoch search and detailed timing analysis of millisecond pulsars in the GC M2, using the Five-hundred-meter Aperture Spherical Telescope. We have discovered two new binary millisecond pulsars in M2, designated M2F and M2G, respectively. We provide measurements of the emission properties of all known pulsars in M2, including their polarization profiles, rotation measures, flux densities, scintillation characteristics, and so forth. In particular, we report the first rotation measure at the distance and direction of this cluster. Additionally, we report the first phase-coherent timing solutions for the M2 pulsars. From our Bayesian timing analysis, we have measured their spin and orbital parameters with high precision, including the advance of periastron for M2A and M2E indicating total system masses of 1.75(13) and 1.80(5) solar masses respectively. Using archival data from the Hubble Space Telescope, we have identified an optical counterpart of M2C, which is likely the white dwarf companion of the pulsar. By combining results from optical and radio observations, we have reconstructed the binary evolution track of this system and estimated the cooling age of the companion to be approximately 10\,Myr, making it the youngest white dwarf in any known GC binary pulsars. Furthermore, using the spin period derivatives of M2 pulsars, we have investigated the gravitational potential of the cluster and found that our results strongly support the latest central-stellar-velocity dispersion measurement in M2.

We present a suite of dynamical simulations designed to explore the orbital and accretion properties of compact (2--7 AU) symbiotic systems, focusing on wind accretion, drag forces, and tidal interactions. Using three levels of physical complexity, we model systems of accreting white dwarfs (WDs) with masses of 0.7, 1.0, and 1.2 M$_\odot$ orbiting evolving Solar-like stars with 1, 2, and 3 M$_\odot$. We show that systems alternate between standard wind accretion and Wind Roche Lobe Overflow (WRLO) regimes during periods of high mass-loss rate experienced by the donor star (the peak of red giant phase and/or thermal pulses). For some configurations, the standard wind accretion has mass accretion efficiencies similar to those obtained by WRLO regime. Tidal forces play a key role in compact systems, leading to orbital shrinkage and enhanced accretion efficiency. We find that systems with high-mass WDs ($\geq 1$ M$_\odot$) and massive donors (2--3 M$_\odot$) are the only ones to reach the Chandrasekhar limit. Interestingly, the majority of our simulations reach the Roche lobe overflow condition that is not further simulated given the need of more complex hydrodynamical simulations. Our analysis shows that increasing physical realism, by including drag and tides, systematically leads to more compact final orbital configurations. Comparison with compact known symbiotic systems seems to suggest that they are very likely experiencing orbital decay produced by tidal forces.

We present an analytical expression that gives both the matter and tracer (halo or galaxy) power spectrum with 1-loop corrections that include the neutrino effects on the mode coupling kernels. We use the FFTLog algorithm to accelerate calculating the higher-order corrections to the power spectrum. We then use our power spectrum and bispectrum models to pursue two main goals. First, we examine the impact of neutrino mass on cosmological parameter estimation from both the power spectrum and bispectrum in real space. We create 1-loop power spectrum and bispectrum templates in real-space and fit to the \texttt{Quijote} simulation suite, including the cross-covariance between the power spectrum and the bispectrum. We show the neutrino signature kernels estimate the same cosmological parameters as the model with the SPT (Standard Perturbation Theory) kernels, even for DESI Year 5 volume, except for the galaxy bias parameters inferred from the bispectrum. Second, we investigate to what extent the bispectrum can improve parameter constraints. We perform a Fisher forecast using the power spectrum, the tree-level bispectrum, and a joint analysis that includes the cross-covariance between them. We show that including the bispectrum can substantially reduce the error bars on key parameters. For the neutrino mass in particular, the uncertainty is reduced by $\sim 20\%$

N-Point Correlation Functions, usually with N = 2, 3, and their Fourier-space analogs power spectrum and bispectrum, are major tools used in cosmology to capture the clustering of large-scale structure. We outline how the clustering these functions capture emerges, explain that inflation produces a 2PCF or power spectrum but that subsequent evolution eventually produces a 3PCF or bispectrum, and beyond (and that inflation may do so as well at some level). Furthermore, in principle the Universe also has a 4PCF or trispectrum, and even clustering beyond. For each of these tools, we discuss the motivation, the practical details of how they are estimated, the current algorithms used to compute them, the theory behind them, and recent applications to data. Throughout, we focus on positioning the reader to find and apply these algorithms with some understanding, linking to public code for each algorithm to the fullest extent possible.

The radiation physics of bright prompt optical emission of gamma-ray bursts (GRBs) remains a puzzle. Assuming that the GRB ejecta is structured, we investigated this issue by characterizing the ejecta as an ultra-relativistic uniform jet core surrounded by a mild-relativistic cocoon. The mixed jet-cocoon (MJC) region can accelerate particles through the shear acceleration mechanism. Parameterizing the radial velocity profile of the MJC region with an exponential function and assuming a uniform magnetic field configuration, we show that the synchrotron radiation of the shear-accelerated electrons can produce a bright optical flash. Emission of the self-synchrotron Compton (SSC) process of the electron population can result in an X-ray excess and an extra MeV-GeV gamma-ray flash relative to the Band function component in the keV-MeV band, which is attributed to the synchrotron radiation of the shock-accelerated electrons in the jet core. Our model reasonably represents the extremely bright optical flash and spectral characteristics of GRBs 990123, 080319B, and 130427A. The inferred magnetic field strength of the MJC region is above $10^{5}$ G, potentially suggesting that the jets of these GRBs are highly magnetized.

We present a general analytic framework to assess whether impact ejecta launched from the surface of a satellite can escape the gravitational influence of the planet--satellite system and enter heliocentric orbit. Using a patched-conic approach and defining the transition to planetocentric space via the Hill sphere or sphere of influence, we derive thresholds for escape in terms of the satellite-to-planet mass ratio and the ratio of the satellite's orbital speed to its escape speed. We identify three dynamical regimes for ejecta based on residual speed and launch direction. We complement this analysis with the circular restricted three-body problem (CR3BP), deriving a necessary escape condition from the Jacobi integral at $\mathrm{L_{2}}$ and showing that it is consistent with the patched-conic thresholds. Applying our model to the Earth--Moon system reveals that all three outcomes--bound, conditional, and unbound--are accessible within a narrow range of launch speeds. This behavior is not found in other planetary satellite systems, but may occur in some binary asteroids. The framework also shows that the Moon's tidal migration has not altered its propensity to produce escaping ejecta, reinforcing the plausibility of a lunar origin for some near-Earth asteroids.

Solar activity drives space weather, affecting Earth's magnetosphere and technological infrastructure, which makes accurate solar flare forecasting critical. Current space weather models under-utilize multi-modal solar data, lack iterative enhancement via expert knowledge, and rely heavily on human forecasters under the Observation-Orientation-Decision-Action (OODA) paradigm. Here we present the "Solar Activity AI Forecaster", a scalable dual data-model driven framework built on foundational models, integrating expert knowledge to autonomously replicate human forecasting tasks with quantifiable outputs. It is implemented in the OODA paradigm and comprises three modules: a Situational Perception Module that generates daily solar situation awareness maps by integrating multi-modal observations; In-Depth Analysis Tools that characterize key solar features (active regions, coronal holes, filaments); and a Flare Prediction Module that forecasts strong flares for the full solar disk and active regions. Executed within a few minutes, the model outperforms or matches human forecasters in generalization across multi-source data, forecast accuracy, and operational efficiency. This work establishes a new paradigm for AI-based space weather forecasting, demonstrating AI's potential to enhance forecast accuracy and efficiency, and paving the way for autonomous operational forecasting systems.

We identify a sample of 324 red and 273 blue face-on spiral galaxies selected from 115 low-redshift (0.014 < z < 0.18) galaxy clusters imaged with CFHT+MegaCam in u- and r-band, KPNO 0.9-meter 2TkA and MOSAIC 8K camera in B and Rc, and images and catalogs extracted from the WINGS survey. Multi-wavelength photometry and spectroscopy were obtained by cross-matching sources with SDSS, GALEX, and WISE datasets. Our main results suggest that up to 45% of optically red spirals are dusty compared to blue spiral galaxies based on infrared observations. The presence of dust can obscure star formation and hence lead to red spirals being misclassified as passive systems. Approximately half of the red spirals do not show evidence of a large abundance of dust, hence are optically red due to passive evolution. Support for the passive nature of these red spirals is provided by SDSS emission line data based on the Dn(4000) spectral index, EW(H-alpha), EW(H-delta), and [O III] 5007 A luminosity, and on a comparison of the star formation rate and the specific star formation rate with cluster blue spirals. Red spirals are an important link in the evolution of galaxies in the high-density cluster environment and play a key role in determining the physical mechanisms that are responsible for transforming blue star-forming galaxies into red spiral systems.

Recent observations and simulations have shown that a buckled bar in the face-on view can be considered as a combination of a long flat bar and a short round barlens (corresponding to the boxy/peanut bulge in the edge-on view). However, the barlens component can be misidentified as the bulge, potentially leading to inaccurate bulge parameter measurements in two-dimensional (2D) image decomposition. Our goal is to explore the optimal method for modeling the barlens component and to understand its impact on bulge parameter measurements in 2D image decomposition. We first analyze mock images from two different simulations (with/without bulge) to verify our decomposition method. We then apply the method to two nearby barred galaxies, NGC 1533 and NGC 7329, from the Carnegie-Irvine Galaxy Survey (CGS). Using GALFIT, we conduct 2D image decomposition by gradually increasing the complexity of model configurations. We also explore the effects of inclination by projecting the simulated galaxy to various viewing angles and analyzing the variations in bulge and barlens parameters. From the mock images, we find that the bulge-to-total ratio (B/T) could be overestimated by 50$\%$ without considering the barlens component; the S\'ersic index and effective radius of the bulge are also affected to varying degrees. The decomposition results of the two CGS galaxies are consistent with our mock image tests. Uncertainties of the structural parameters of the bulge and barlens are larger at higher inclination angels due to the strong projection effect in the central region. Our findings underscore the necessity of accurately modeling the barlens, revealing that its inclusion in 2D image decomposition can lead to a decrease in B/T by $\sim$30-50$\%$, with other bulge parameters, such as the S\'ersic index and effective radius, also affected.

{The multiple outburst events of comet 12P/Pons-Brooks during its 2024 apparition offer a unique window into highly-active volatile releasing processes not observable during quiescent periods. We performed radio observations of comet 12P/Pons-Brooks with the Tianma-65m radio telescope, targeting the OH and NH$_3$ inversion lines at 18-cm and 1.3-cm, respectively. By monitoring 12P at different heliocentric distances on its inbound journey, we aim to provide insights into the comet's volatile composition and outburst behavior. Four observations were carried out between December 2023 and March 2024 when the comet was approaching the Sun from 2.22 AU to 1.18 AU. We conducted 18-cm OH lines observations on 4 single days using the cryogenically cooled receiver system of the telescope to derive $\rm H_{2}O$ production rate. During 12P's outburst on December 14, we also conducted observations targeting the $\rm NH_{3}$ emission. OH 18-cm lines were clearly detected with a signal-to-noise ratio of $\sim$4$\sigma$ (peak intensity). A tentative detection of $\rm NH_{3}$ was made at the $\sim$$3\sigma$ level during the outburst phase, but the detection needs to be further verified. Our observations provide information on the outgassing behavior of 12P/Pons-Brooks during its 2024 apparition. The water production rate of 12P, derived from the 18-cm OH lines is consistent with measurements obtained in other works. The possible detection of $\rm NH_{3}$ during an outburst suggests possible connections between subsurface volatile reservoir and the outburst mechanism. These results could further our understanding of the composition and activity of Halley-type comets.

Context. Previous studies have suggested that the Sun is relatively depleted in refractory elements compared to other solar twins or analogs, potentially as a result of planet formation. However, such conclusions are often limited by inhomogeneous samples and a lack of direct comparison with stars known to host planets. Aims. We aim to perform a homogeneous and precise abundance analysis of solar twins and analogs that host planets, to investigate possible chemical signatures associated with planet formation. Methods. We obtain high-resolution, high signal-to-noise ratio Magellan/MIKE spectra for 25 solar-like stars, including 22 confirmed or candidate planet hosts and three comparison stars. Stellar parameters and elemental abundances for 23 elements (from C to Eu) are derived through a strict line-by-line differential analysis relative to the Sun. Results. Our sample spans [Fe/H] = -0.23 to +0.18 dex and includes 20 solar analogs, six of which are solar twins. Typical abundance uncertainties range from 0.01 to 0.05 dex for lighter elements (e.g., Fe, Si, C, O, Na) and up to 0.1 dex for neutron-capture elements. The Sun is consistently depleted in refractory elements relative to all solar analogs and twins, regardless of planet type. Stars hosting small planets tentatively show slightly stronger refractory element depletion than those hosting giant planets, though the difference is not yet statistically significant. Conclusions. We emphasize the need for strictly differential, line-by-line analyses relative to the Sun, as well as careful consideration of systematic differences between instruments, to ensure consistency and the homogeneity required to achieve our goals.

A search has been carried out for the pulsar J0311+1402, which has a period of $P = 40.9$ s, in the data archive of the Large Phased Array (LPA) radio telescope. When searching using fast folding algorithm (FFA), periodic pulsar radiation at a frequency of 111 MHz was not detected. In 3321 observation sessions lasting 5 minutes, 35 strong pulses were detected with a signal-to-noise ratio (S/N) greater than 10. Some of the pulses have a complex multi-peak structure consisting of narrow details, while some of the pulses are single-component. The peak flux densities of the details of these strong pulses range from 2 to 11 Jy. The peak value ($S_{\rm p} = 2$\,Jy) and the integral ($S_{\rm i} = 7$\,mJy) flux density in the average profile were obtained from the strong pulses. It is shown that pulsar pulses in the meter-wavelength range arrive sporadically, and the pulsar is similar in its properties to a rotating radio transient (RRAT). The pulsar has the minimal dispersion measure, the minimal distance from the Sun, and the minimal pseudo-luminosity of all known pulsars. Pulsar timing made it possible to improve the previously obtained value of the period ($P$) and to estimate the period derivative ($\dot P$). In the dependency of timing residuals (TRs) from the times of arrival (TOA) of pulses discontinuities are visible, when no pulses were observed. The duration of these breaks can be hundreds of days.

In this paper, we investigate the inflationary phenomenology of parity-violating (PV) extensions of symmetric teleparallel gravity by applying this PV gravity theory to axion inflation. The presence of PV terms induces velocity birefringence in the tensor perturbations. During inflation, when the inflaton rapidly traverses the cliff-like region in its potential, the tensor modes at specific scales for one of the two circular polarization states undergo significant amplification due to tachyonic instability. Consequently, the resulting primordial gravitational waves (GWs), characterized by a one-handed polarization and a multi-peak structure in their energy spectrum, exhibit a significant amplitude potentially detectable by LISA and Taiji, and their chirality could be determined by the LISA-Taiji network. The detection of such a chiral GW signal provides an opportunity to probe inflation and PV gravity theory.

In this work, we test the cosmic distance duality relation (CDDR) by combining Pantheon+ Type Ia supernova (SNe Ia) data and DESI DR2 baryon acoustic oscillation (BAO) measurements. To resolve the redshift mismatch between the two datasets, we develop a new method called Neural Kernel Gaussian Process Regression (NKGPR), which uses two neural networks to simultaneously learn the mean and kernel functions of a Gaussian process. This approach improves upon traditional Gaussian process regression by mitigating trend mismatches and removing the need for manual kernel selection. We investigate possible deviations from the CDDR by adopting three parameterizations of the deviation function and constrain the model-independent parameter $\eta_0$ through a marginalized likelihood analysis. Our results show no significant departure from the expected relation, confirming the consistency of the CDDR within current observational uncertainties.

We used the NSF Jansky Very Large Array at a frequency $\nu =$ 22\,GHz to study the nearest billion-solar-mass black hole, in the early-type galaxy NGC\,3115 at a distance of 9.7\,Mpc. We localize a faint continuum nucleus, with flux density $S_{\rm 22\,GHz} = 48.2\pm6.4\,\mu$Jy, to a FWHM diameter $d_{\rm 22\,GHz} <$ 59\,mas (2.8\,pc). We find no evidence for adjacent emission within a stagnation region of radius $R_{\rm sta} \sim$ 360\,mas (17\,pc) identified in a recent hydrodynamic simulation tailored to NGC\,3115. Within that region, the simulated gas flow developed into an advection-dominated accretion flow (ADAF). The nucleus' luminosity density $L_{\rm 22\,GHz} = 5.4 \times 10^{17}\,\rm W\,Hz^{-1}$ is about 60 times that of Sagittarius\,A$^\star$. The nucleus' spectral index $\alpha_{\rm 10\,GHz}^{\rm 22\,GHz} = -1.85\pm0.18$ ($S_\nu \propto \nu^\alpha$) indicates optically-thin synchrotron emission. The spectral energy distribution of the nucleus peaks near $\nu_{\rm peak} =$ 9\,GHz. Modeling this radio peak as an ADAF implies a black hole mass $M_{\rm ADAF} = (1.2\pm0.2) \times 10^9\,M_\odot$, consistent with previous estimates of $(1-2) \times 10^9\,M_\odot$ from stellar or hot-gas dynamics. Also, the Eddington-scaled accretion rate for NGC\,3115, $\dot{M}_{\rm ADAF}/\dot{M}_{\rm Edd} = 1.2^{+1.0}_{-0.6} \times 10^{-8}$, is about 4-8 times lower than recent estimates for Sagittarius\,A$^\star$.

Solar extreme ultraviolet (EUV) irradiance plays a crucial role in heating the Earth's ionosphere, thermosphere, and mesosphere, affecting atmospheric dynamics over varying time scales. Although significant effort has been spent studying short-term EUV variations from solar transient events, there is little work to explore the long-term evolution of the EUV flux over multiple solar cycles. Continuous EUV flux measurements have only been available since 1995, leaving significant gaps in earlier data. In this study, we propose a Bayesian deep learning model, named SEMNet, to fill the gaps. We validate our approach by applying SEMNet to construct SOHO/SEM EUV flux measurements in the period between 1998 and 2014 using CaII K images from the Precision Solar Photometric Telescope. We then extend SEMNet through transfer learning to reconstruct solar EUV irradiance in the period between 1950 and 1960 using CaII K images from the Kodaikanal Solar Observatory. Experimental results show that SEMNet provides reliable predictions along with uncertainty bounds, demonstrating the feasibility of CaII K images as a robust proxy for long-term EUV fluxes. These findings contribute to a better understanding of solar influences on Earth's climate over extended periods.

Accurately accounting for mixed-gas opacities is critical for radiative-transfer (RT) calculations in sub-stellar atmospheres. To produce the total k-coefficients of an arbitrary mixture of gases and their associated volume mixing ratios (VMRs), several methods are applied in the literature with various levels of overall accuracy and ease of computation. We propose a simple, tunable random overlap method, polynomial reconstruction and sampling (PRAS). PRAS is a Monte Carlo-based technique, sampling polynomial approximations of the opacity cumulative distribution function (CDF) in a wavelength band for each species requiring mixing. The method enables control over the end accuracy of the opacity mixture through choices in CDF fitting and number of random samples used in the mixing scheme. We find PRAS is typically as accurate, or more accurate, than other methods at recovering individual, pre-mixed k-coefficients. In an emission spectrum comparison test, PRAS, even with a small number of samples (100), is within ~2% of the reference 16+16 Legendre quadrature node random overlap with resorting and rebinning (RORR) results, and is typically more accurate than the 4+4 and 8+8 Legendre node schemes. In the vertical flux and heating rate tests, we also find that PRAS is generally more accurate than other schemes, and an improvement over the adaptive equivalent extinction (AEE) method. Overall, our current tests show PRAS is a generally viable alternative for the calculation of randomly overlapped opacities, especially in scenarios where increased accuracy of the RT calculation is required and when larger numbers of quadrature points are used. PRAS may therefore provide a benefit in performance and accuracy for high-precision retrieval modelling of JWST data.

The hadron production in the simulation of extensive air showers is a long standing problem and the origin of large uncertainties in the reconstruction of the mass of the high energy primary cosmic rays. Hadronic interaction models re-tuned after early LHC data give more consistent results among each other compared to the first generation of models, but still can't reproduce extended air shower data (EAS) consistently resulting in the so-called "muon puzzle". Using more recent LHC data like in the QGSJET-III model improve further the description of EAS by such a model but is not enough to resolve the discrepancy. On the other hand, the EPOS project is a theoretical global approach aiming at describing data from very fundamental electron-positron interactions to central heavy ions collisions. We will demonstrate that this approach can provide new constraints, changing the correlation between the measured data at mid-rapidity and the predicted particle production at large rapidities, which drive the EAS development. Thus, using the same accelerator data, different predictions are obtained in air shower simulations in much better agreement with the current air shower data (for both the maximum shower development depth Xmax and the energy spectrum of the muons at ground). Using the EPOS LHC-R model, the detailed changes will be addressed and their consequences on EAS observable at various energies.

The air shower array Carpet-3 detected a 300 TeV photon from the direction of GRB 221009A at 4536 s after the Fermi-GBM trigger for this event. If the association with this gamma-ray burst is real, it poses two puzzles. First, why was this photon not absorbed by the extragalactic background light? ''New physics'' beyond the Standard Model is required to explain how it managed to reach Earth from a cosmological distance. Second, why was this photon detected when the VHE afterglow observed by LHAASO already faded? A novel astrophysical mechanism is required to explain this delay. In this work we show that Lorentz invariance violation (LIV), which arises as a low-energy limit of certain quantum gravity theories, can solve both puzzles. It shifts thresholds of particle interaction and changes the opacity of the extragalactic background, and cause energy-dependent variations of the photon velocity, which changes the photon time of flight. We investigate the LIV parameter space assuming that the 300 TeV photon is a part of the VHE afterglow detected by LHAASO in the TeV range. We identify viable solutions and place stringent two-sided constraints on the LIV energy scale required to resolve the observational puzzles. First-order LIV appears to be incompatible with the constraints set by analyzing the TeV afterglow of this GRB. Viable solutions emerge for higher orders. In particular, the commonly studied second-order subluminal LIV with $E_{\rm LIV2} = 1.30_{-0.35}^{+0.56} \times 10^{-7} E_{\rm Pl}$ (95.4% credibility level; $E_{\rm Pl}$ is the Planck energy) is consistent with all the observed data.

Many sub-Neptune and super-Earth exoplanets are expected to develop metal-enriched atmospheres due to atmospheric loss processes such as photoevaporation or core-powered mass loss. Thermochemical equilibrium calculations predict that at high metallicity and a temperature range of 300-700 K, CO2 becomes the dominant carbon species, and graphite may be the thermodynamically favored condensate under low-pressure conditions. Building on prior laboratory findings that such environments yield organic haze rather than graphite, we measured the transmittance spectra of organic haze analogues and graphite samples, and computed their optical constants across the measured wavelength range from 0.4 to 25 {\mu}m. The organic haze exhibits strong vibrational absorption bands, notably at 3.0, 4.5, and 6.0 {\mu}m, while graphite shows featureless broadband absorption. The derived optical constants of haze and graphite provide the first dataset for organic haze analogues formed in CO2-rich atmospheres and offer improved applicability over prior graphite data derived from bulk reflectance or ellipsometry. We implemented these optical constants into the Virga and PICASO cloud and radiative transfer models to simulate transit spectra for GJ 1214b. The synthetic spectra with organic hazes reproduce the muted spectral features in the NIR observed by Hubble and general trends observed by JWST for GJ 1214b, while graphite models yield flat spectra across the observed wavelengths. This suggests haze features may serve as observational markers of carbon-rich atmospheres, whereas graphite's opacity could lead to radius overestimation, offering a possible explanation for super-puff exoplanets. Our work supplies essential optical to infrared data for interpreting observations of CO2-rich exoplanet atmospheres.

We present ALMA observations of the Class 0 protostar IRAS 04166+2706, obtained as part of the ALMA large program Early Planet Formation in Embedded Disks (eDisk). These observations were made in the 1.3 mm dust continuum and molecular lines at angular resolutions of $\sim 0.05''$ ($\sim 8$ au) and $\sim 0.16''$ ($\sim25$ au), respectively. The continuum emission shows a disk-like structure with a radius of $\sim22$ au. Kinematical analysis of $^{13}$CO(2-1), C$^{18}$O(2-1), H$_2$CO (3$_{0,3}$-2$_{0,2}$), CH$_3$OH (4$_2$-3$_1$) emission demonstrates that these molecular lines trace the infalling-rotating envelope and possibly a Keplerian disk, enabling us to estimate the protostar mass to be $0.15 \rm{M_\odot} < \rm{M_\star} < 0.39 M_\odot$. The dusty disk is found to exhibit a brightness asymmetry along its minor axis in the continuum emission, probably caused by a flared distribution of the dust and the high optical depth of the dust emission. In addition, the CO(2-1) and SiO(5-4) emissions show knotty and wiggling motions in the jets. Our high angular resolution observations revealed the most recent mass ejection events, which have occurred within the last $\sim 25$ years.

We examine the splashback structure of galaxy clusters using hydrodynamical simulations from the GIZMO run of The Three Hundred Project, focusing on the relationship between the stellar and dark matter components. We dynamically decompose clusters into orbiting and infalling material and fit their density profiles. We find that the truncation radius $r_{\mathrm{t}}$, associated with the splashback feature, coincides for stars and dark matter, but the stellar profile exhibits a systematically steeper decline. Both components follow a consistent $r_{\mathrm{t}}{-}\Gamma$ relation, where $\Gamma$ is the mass accretion rate, which suggests that stellar profiles can be used to infer recent cluster mass growth. We also find that the normalisation of the density profile of infalling material correlates with $\Gamma$, and that stellar and dark matter scale radii coincide when measured non-parametrically. By fitting stellar profiles in projection, we show that $r_{\mathrm{t}}$ can, in principle, be recovered observationally, with a typical scatter of $\sim 0.3\,R_{200\mathrm{m}}$. Our results demonstrate that the splashback feature in the stellar component provides a viable proxy for the cluster's physical boundary and recent growth by mass accretion, offering a complementary observable tracer to satellite galaxies and weak lensing.

We present the discovery of a correlation, in a sample of 16 gamma-ray burst 8.5 GHz radio afterglows, between the intrinsic luminosity measured at 10 days in the rest frame, $L_{\mathrm{Radio,10d}}$, and the average rate of decay past this time, $\alpha_{>10d}$. The correlation has a Spearman's rank coefficient of $-0.70 \pm 0.13$ at a significance of $>3\sigma$ and a linear regression fit of $\alpha_{>10d} = -0.29^{+0.19}_{-0.28} \log \left(L_{\mathrm{Radio,10d}} \right) + 8.12^{+8.86}_{-5.88}$. This finding suggests that more luminous radio afterglows have higher average rates of decay than less luminous ones. We use a Monte Carlo simulation to show the correlation is not produced by chance or selection effects at a confidence level of $>3\sigma$. Previous studies found this relation in optical/UV, X-ray and GeV afterglow light curves, and we have now extended it to radio light curves. The Spearman's rank coefficients and the linear regression slopes for the correlation in each waveband are all consistent within $1\sigma$. We discuss how these new results in the radio band support the effects of observer viewing geometry, and time-varying microphysical parameters, as possible causes of the correlation as suggested in previous works.

The Cosmology Redshift Survey of the 4-metre Multi-Object Spectroscopic Telescope (4MOST-CRS) will provide redshift measurements of galaxies and quasars over 5700{\degsq} in the southern hemisphere. As targets for the 4MOST-CRS, we present a selection of an $r<19.25$ magnitude limited sample of Bright Galaxies (BG) and a colour selected sample of Luminous Red Galaxies (LRG) based on DESI Legacy Survey DR10.1 photometric data, in the redshift ranges $0.1<z<0.5$ and $0.4<z<1$, respectively. These samples are selected using the $g$, $r$, $z$, and $W1$ (from unWISE) photometric bands. For BGs, the star--galaxy separation is performed based on Gaia and Tycho-2 star catalogues. Following 4MOST requirements, the target densities of BGs and LRGs are 250{\mdegsq} and 400{\mdegsq}, respectively. We quantified the stellar contamination to be $<2-4\%$ for both galaxy samples using data from the first DESI data release. Using angular clustering, we show that both samples are robust against imaging systematics, confirming a low stellar contamination. Finally, we provide forecasts of the baryonic acoustic oscillation (BAO) and growth of structure ($\sigma_8$) measurements from the 4MOST-CRS alone and in combination with DESI. From the 4MOST-CRS, we expect 3\% and 25\% precision on BAO and $\sigma_8$ measurements, respectively. Combining 4MOST-CRS with DESI improves the constraints from DESI alone by 12$\%$ in the 0.4 < z < 0.8 redshift range, leading to the most stringent constraints on BAO measurements from spectroscopic galaxy clustering.

We investigate observational signatures of ultralight vector dark matter with masses $m \sim 10^{-24}$-$10^{-22}$ eV in pulsar timing arrays, taking into account general polarization states of the vector field. We find that vector dark matter induces pulsar timing residuals with nontrivial directional dependence, reflecting the anisotropic property and polarization structure specific to vector dark matter, unlike scalar dark matter. We also derive angular correlation curves of the timing residuals. Intriguingly, circular polarization of the vector dark matter enhances the quadrupole nature of the correlation curve, resulting in a more notable bending of the Hellings-Downs curve. The derived correlation curves offer a useful means to distinguish gravitational wave and dark matter contributions and to probe the nature of dark matter.

We investigate the rescattering effects arising from non-minimally coupled scalar particles $\chi$ that are suddenly produced during inflation. The coupling term $\xi R \chi^2$ significantly enhances resonant particle production compared to minimal coupling scenarios. Consequently, the produced $\chi$ particles rescattering off the homogeneous inflaton condensate $\phi$, generating abundant $\delta\phi$ quanta within very short time intervals. This process leads to characteristic enhancements in the power spectrum of primordial curvature perturbations at scales corresponding to the moments of particle production. When this occurs at small scales, the power spectrum amplitude can reach as high as $\mathcal{O}(10^{-2})$. Furthermore, analysis of the equilateral bispectrum shows that this mechanism also induces substantial non-Gaussian features.

The combined Planck, BICEP/Keck Array and BAO measurements of the scalar spectral index and the tensor-to-scalar ratio from the cosmic microwave background observations severely constrain or completely rule out several models of inflationary potentials. On the other hand, the data seems to favor concave potentials over convex ones. In this paper, we study preheating and gravitational waves after inflation in a large-field, regularized hilltop potential where inflation takes place in the concave plateau. The inflaton, $\phi$, is coupled to a subdominant scalar field, $\chi$, through a quartic coupling. After inflation ends, $\phi$ oscillates about the potential minimum and becomes inhomogeneous. The growth of the fluctuation modes, $\delta\phi_k$ and $\delta\chi_k$, in a homogeneous, oscillating background is analyzed in linear perturbation theory, revealing that small modes likely experience broad self-resonance or external parametric resonance. To determine if the resonances are sufficiently strong to cause unstable growth of the modes we perform a lattice simulation. The lattice simulations demonstrate that, although the initial inhomogeneities generate a stochastic gravitational wave background that remains below the present observational limit, the fluctuations do not grow exponentially, and the occupation numbers of $\delta\phi_k$ and $\delta\chi_k$ remain close to zero.

This study presents the first extended comparison of cosmic filaments identified in SDSS DR10 observations ($z < 0.05$) and the IllustrisTNG300-1 $\Lambda$CDM simulation ($z = 0$), utilizing the novel GrAviPaSt filament-finder method. The analyses are performed on both macro- and micro-filaments, each characterized by their length, thickness, and contrast in mass density. In addition to total sample comparisons, two subcategories of micro-filaments, GG (linking galaxy groups) and CC (linking galaxy clusters), are introduced to further analyze discrepancies between the $\Lambda$CDM model and observation. While $\Lambda$CDM produces extended macro-filaments, such structures are largely absent in SDSS, and where present, they exhibit higher densities than their simulated counterparts. Micro-filaments also show notable density discrepancies: at fixed length and thickness, observational filaments are significantly denser than those in the simulation. Employing radial density profiles reveal that micro-filaments in the $\Lambda$CDM simulation exhibit higher contrasts in mass density relative to the background compared to their observational counterparts. Notably, CC type micro-filaments displayed enhanced density contrasts over GG types in the simulation, while observational data showed the opposite trend. Furthermore, SDSS galaxies in both GG and CC micro-filaments exhibit lower specific star formation rates (sSFR) and older stellar populations, while TNG300-1 micro-filaments host more actively star-forming galaxies within the intermediate stellar mass range. These results reveal persistent discrepancies between observational data and the $\Lambda$CDM reconstruction of cosmic filaments, pointing to possible tensions in our current understanding of large-scale structures and their environmental effects on galaxy evolution.

The cluster environment can have a significant impact on galaxy evolution. We study the impact that passage through a cluster has on stellar and ionised gas kinematics for galaxies within the Sydney-AAO Multi Integral field (SAMI) Galaxy Survey. We compute the kinematic asymmetry $v_{\rm asym}$ in the line-of-sight stellar and ionsied gas velocity maps to quantify how the cluster environment disturbs the kinematics of the stars and ionised gas. We find a significantly higher fraction of galaxies with elevated gas asymmetries in clusters compared to non-cluster environments (17$^{+2}_{-3}$\%, 26/154 vs. 11$^{+1}_{-1}$\%, 72/751), with these galaxies most likely being recent infallers passage based on their position in projected-phase-space. Compared to cluster galaxies without elevated gas asymmetries, cluster galaxies with elevated gas asymmetries have, on average, more centrally concentrated star-formation. Finally, we find the highest fraction of galaxies with elevated gas asymmetries in clusters likely to host significant substructure or be dynamically complex. Our findings are consistent with the scenario of galaxies falling into clusters, either individually or in groups, and undergoing disk-fading and a redistribution of gas, due to ram pressure stripping experienced during pericentre passage.

OB associations, as an intermediate stage between Galactic clusters and field stars, play an important role in understanding the star formation process, early stellar evolution, and Galactic evolution. In this work, we construct a large sample of OB stars with 6D phase space parameters ($l, b, d, V_{\rm los}, pmra ,pmdec$) by combining the distances from Bailer-Jones et al. (2021), radial velocities derived from low-resolution spectra of the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST), and proper motions from the \textit{Gaia} Data Release 3 (DR3). This sample includes 19,933 OB stars, most of which are located within 6\,kpc of the Sun. Using 6D phase space parameters and friends-of-friends clustering algorithm, we identify 67 OB associations and 112 OB association candidates, among them, 49 OB associations and 107 OB association candidates are newly identified. The Galactic rotation curve derived using 67 OB association members is relatively flat in the range of Galactocentric distances 7$<$$R$$<$13\,kpc. The angular rotation velocity at solar Galactocentric distance of $R_\odot$ =8.34\,kpc is $\Omega_0$ = 29.05$\pm$0.55\,km\,s$^{-1}$\,kpc$^{-1}$. The spatial distribution of the 67 OB associations indicates that they are mainly located at low Galactic latitudes and near spiral arms of the Milky Way. Additionally, we estimate the velocity dispersions and sizes of these 67 OB associations. Our results show that the velocity dispersions decrease as Galactocentric distances increase, while their sizes increase as Galactocentric distances increase.

We analyzed X-ray data from Chandra, XMM-Newton, NICER, and NuSTAR to characterize the properties of the pulsar PSR J1838$-$0655 and its pulsar wind nebula (PWN) associated with HESS J1837$-$069. Based on 5.5 years of NICER monitoring, we detected a glitch around MJD 59300, characterized by a fractional frequency jump of approximately $2\times 10^{-6}$. We constructed semi-phase-coherent timing solutions for pre- and post-glitch epochs, allowing for phase alignment of multi-instrument data and a subsequent measurement of the pulsed spectrum of the pulsar. This analysis confirmed previously-reported spectral curvature and revealed a peak energy of $73^{+85}_{-26}$ keV in the pulsar's spectral energy distribution (SED), based on a logpar model fit of the pulsed spectrum. We discuss these findings within the framework of pulsar magnetospheric emission scenarios. The PWN's X-ray spectrum is well-described by a power law with a photon index of $2.1\pm0.3$, softer than previously-reported measurements. We also characterized the X-ray emission from another extended X-ray source AX J1837.3$-$0652 within the extent of HESS J1837$-$069. Based on the spatial and spectral properties of these X-ray sources, we propose a leptonic emission scenario for HESS J1837$-$069 and demonstrate its feasibility through SED modeling. Finally, we discuss the implications of our model results and alternative scenarios for the gamma-ray emission.

Subhalos play a crucial role in accurately modeling galaxy formation and galaxy-based cosmological probes within the highly nonlinear, virialized regime. However, numerical convergence of subhalo evolution is difficult to achieve, especially in the inner regions of host halos where tidal forces are strongest. I investigate the numerical convergence and correction methods for the abundance, spatial, and velocity distributions of subhalos using two $6144^3$-particle cosmological N-body simulations with different mass resolutions -- Jiutian-300 ($1.0 \times 10^{7}\,h^{-1}M_{\odot}$) and Jiutian-1G ($3.7 \times 10^{8}\,h^{-1}M_{\odot}$) -- with subhalos identified by HBT+. My study shows that the Surviving subhalo Peak Mass Function (SPMF) converges only for subhalos with $m_{\mathrm{peak}}$ above $5000$ particles but can be accurately recovered by including orphan subhalos that survive according to the merger timescale model of Jiang et al., which outperforms other models. Including orphan subhalos also enables recovery of the real-space spatial and velocity distributions to $5$--$10\%$ accuracy down to scales of $0.1$--$0.2\,h^{-1}\mathrm{Mpc}$. The remaining differences are likely due to cosmic variance and finite-box effects in the smaller Jiutian-300 simulation. Convergence below $0.1\,h^{-1}\mathrm{Mpc}$ remains challenging and requires more sophisticated modeling of orphan subhalos. I further highlight that redshift-space multipoles are more difficult to recover even at larger scales because unreliable small-scale pairs at $r_{\mathrm{p}} < 0.1\,h^{-1}\mathrm{Mpc}$ in real space affect scales of tens of $\mathrm{Mpc}$ in redshift space due to elongated Fingers-of-God effects. Therefore, for redshift-space statistics, I recommend using modified or alternative measures that reduce sensitivity to small projected separations in subhalo-based studies.

Fast radio bursts (FRBs) are millisecond-duration extragalactic radio transients of unknown origin, and studying their host galaxies could offer clues to constrain progenitor models. Among various host properties, gas-phase metallicity is a key factor influencing stellar evolution and the production of transients. We analyze the largest uniformly selected sample of FRB host galaxies to date, measuring oxygen abundances (12+log(O/H) = 8.04-8.84) for 40 hosts using consistent emission-line diagnostics. Using a volume-limited subsample, we compare the distributions of stellar mass, star formation rate (SFR), and metallicity to a control sample of star-forming galaxies matched in the same selection criteria. We find that FRB host galaxies span a wide range in metallicity and are broadly consistent with the SFR-weighted mass-metallicity relation of the star-forming galaxy population. Contrary to the earlier claim in the literature, we find no clear lower bound on metallicity, suggesting that metallicity alone does not strictly regulate FRB production. Encouragingly, this implies FRBs can form even in low-metallicity, high-redshift galaxies, supporting their potential as probes of matter distribution across cosmic time. Additionally, we find marginal ($\sim$2$\sigma$) evidence for a -0.09 $\pm$ 0.04 dex metallicity offset from the fundamental metallicity relation, likely due to suppressed SFRs at fixed mass and metallicity rather than metal deficiency. This offset resembles that observed in local post-merger galaxies, and may reflect a post-starburst phase following galaxy interactions, where FRB progenitors formed during the starburst produce FRBs after a 100-500 Myr delay, consistent with observed delay-time distributions and favoring binary evolution channels over core-collapse supernovae.

We show that the observed 60Fe/26Al flux ratio provided by the SPectrometer on INTEGRAL satellite (0.24 +- 0.04) can be reproduced only if rotation is taken into account in the computation of the stellar models. Predictions from non-rotating stellar models yield to a significantly lower ratio (0.062), which is incompatible with the observed value. The adopted models and the associated yields are based on a combination of models already published by Limongi & Chieffi (2018) complemented by additional ones fully consistent with the original grid, allowing a finer resolution in the initial rotational velocity distribution.

Evolution of stars with initial masses $M_\mathrm{ZAMS}=1.1M_\odot$, $1.3M_\odot$, $1.5M_\odot$ and relative mass abundances of metals $Z=0.006$ and 0.02 was computed from the main sequence up to the final AGB stage. Selected models of evolutionary sequences were used as initial conditions for solution of the equations of hydrodynamics describing pulsations of red giants, whereas for each evolutionary sequence of Mira variables pulsating in the fundamental mode we determined the theoretical period-luminosity relation. A change in the metal abundance is shown to substantially affect the period-luminosity relation because of significant growth of the slope with decreasing $Z$. In particular, Mira variables of the LMC ($Z=0.006$) are brighter by 0.2-0.5 mag than galactic Mira variables ($Z=0.02$) with same pulsation periods. The low boundary of fundamental mode pulsations changes from $\Pi\approx 70$ day for $Z=0.02$ to $\Pi\approx 120$ day for $Z=0.006$.

Gamma-ray bursts (GRBs) are bright flashes of electromagnetic radiation originating from the core collapse of massive stars or the merger of compact objects. It has long been theorized that GRBs can emit very high-energy (VHE) gamma rays that can reach the TeV level. Although current-generation Imaging Atmospheric Cherenkov Telescopes (IACTs), such as H.E.S.S., have been observing GRBs since 2002, the first detection of GRBs by IACTs occurred only 16 years later, in 2018, raising the question of why no detections were made during these years. We investigate all GRBs detected by the Swift Observatory with redshift measurements over the past two decades. Using the phenomenological relationship between X-ray and gamma rays and taking into consideration extragalactic background light absorption effects and instrument response functions, we search for any missed opportunities for GRBs that could have been detected by the three IACTs: H.E.S.S., MAGIC, and VERITAS, and present the best candidates. We find that the missing detections can be explained by the low rate of detectable GRBs at VHE, which we quantify as < 1 per year. We also find that with the future Cherenkov Telescope Array Observatory (CTAO), this rate can increase to 4 per year.

The rise of direct detection of gravitational waves (GWs) started a new era in multi-messenger astrophysics. Like GWs, many other astrophysical transient sources suffer from poor localization, which can span tens to thousands of square degrees in the sky. Moreover, as the detection horizon for these transients widens and the detection rate increases, current electromagnetic follow-up facilities require tools to optimize the follow-up of poorly localized events and save valuable telescope time for their time-domain astrophysics programs. We present \texttt{tilepy}, a Python library, and a tool to optimize the follow-up of poorly localized transient events. \texttt{tilepy} is used for GWs as well as other poorly localized events such as gamma-ray bursts detected by Fermi-GBM and neutrino candidates from IceCube. \texttt{tilepy} has also been optimized to integrate smoothly with multiple ground-based observatories operating individually or simultaneously with diverse observational configurations. In this contribution, we introduce the latest developments from \texttt{tilepy}, mainly the ability to operate with space-based observatories while taking into consideration factors such as Earth, Sun, and Moon occultation and South Atlantic Anomaly passage. We present innovations to the platform, handling a variety of field of view shapes, the possibility of optimizing observation scheduling with artificial intelligence tools and examples of its use on transient astrophysical events.

The Blooming Tree (BT) algorithm, based on the hierarchical clustering method, is designed to identify clusters, groups, and substructures from galaxy redshift surveys. We apply the BT algorithm to a wide-field ($10\times 10$ deg$^2$) spectroscopic dataset centered on the galaxy cluster A2029. The BT algorithm effectively identifies all the X-ray luminous clusters and most of the optical clusters known in the literature, numerous groups, and the filaments surrounding the clusters, associating a list of galaxy members to each structure. By lowering the detection threshold, the BT algorithm also identifies the three superclusters in the field. The BT algorithm arranges the clusters and groups that make up the superclusters in a hierarchical tree according to their pairwise binding energy: the algorithm thus unveils the possible accretion history of each supercluster and their future evolution. These results show how the BT algorithm can represent a crucial tool to investigate the formation and evolution of cosmic structures on non-linear and mildly non-linear scales.

We performed the spectral and temporal analysis of MAXI J1803-298 using AstroSat/LAXPC and NICER observations taken in May 2021 during the initial phase of the outburst. We found that the source traverses through the hard, intermediate, and soft spectral states during the outburst. The spectrum in all states can be described using soft emissions from the thermal disk and hard emissions from the coronal regions. The variation in the inner disk temperature and normalization of the disk indicates the motion of the truncated disk across these different spectral states. We confirmed the presence of broad features, Type-C, and Type-B QPOs in the power spectra of different spectral states. We investigated the fractional rms and lags of all the variability features and discovered that the lag swung between positive and negative during the outburst evolution. While modeling the features with a simple model that considers variations in accretion parameters such as the accretion rate, heating rate, and inner disk radius, along with delays between them, we found a dynamic reversal in the origin of variability between the corona and the disk. Furthermore, our results are consistent with previous works and a radio study conducted on this source during its outburst.

We report the finding of a linear, non-axisymmetric, global instability in gas discs around stars, which may be relevant to other astrophysical discs. It takes the form of an $m=1$ mode that grows in the disc density distribution while the star-barycentre distance rises exponentially with a characteristic timescale that is orders of magnitude longer than the orbital period. We present results of hydrodynamical simulations with various codes and numerical methods, using either barycentric or stellocentric reference frames, with or without the disc's self gravity: all simulations consistently show an unstable mode growing exponentially. The instability disappears if, and only if, the reflex motion of the star due to the disc's asymmetry is not taken into account in the simulations. For this reason we refer to this instability as the reflex instability. We identify a feedback loop as a possible origin, whereby the acceleration of the star excites the eccentricity of the disc, yielding an $m=1$ mode in the density distribution which, in turn, pulls the star. The growth timescale of the instability decreases with increasing disc mass and is a few hundred orbits for disc-to-star mass ratios of a few percent. If truly physical, and not due to a numerical artifact that would be common to all the codes we have employed, the reflex instability could have a dramatic impact on protoplanetary discs evolution and planetary formation.

Context. Solar flux atlases observe the spatially integrated light from the Sun, treating it as a star. They are fundamental tools for gaining insight into the composition of the Sun and other stars, and are utilized as reference material for a wide range of solar applications such as stellar chemical abundances, atmospheric physics, stellar activity, and radial velocity signals. Aims. We provide a detailed comparison of solar activity in some of the well-known solar atlases against the new High Accuracy Radial velocity Planet Searcher for the Northern hemisphere (HARPS-N) Quiet Sun (QS) and measured activity (MA) atlases that are published, for the first time, in this work. Methods. Ten of the widely used individual spectral lines from each flux atlas were selected to compare solar activity using three methods: 1) Equivalent Widths 2) Activity number, a novel activity measure which we introduce in this work. 3) Bisectors and radial velocity. Results. The significantly smaller activity measured in the MA atlas compared to the other atlases, relative to the QS atlas, underscores the dominance of instrumental effects over solar activity in their impact on spectral lines, which cannot be corrected through simple line convolution to match resolutions of other atlases. Additionally, our investigation unexpectedly revealed a substantial intensity shift in the Ca ii H & K lines of other atlases compared to our HARPS-N atlases, likely caused by assumptions in normalisation techniques used in the early Kitt Peak atlases. Conclusions. With an average spot number of zero, our QS atlas is well suited to serve as an absolute benchmark atlas representative of solar minimum for the visible spectrum that other atlases can be compared against. Our recommendations are 1) publication of a detailed log along with the observations, to include exact dates and indications of solar activity...

Giant Low Surface Brightness (GLSB) galaxies are extreme disk systems with exceptionally large sizes and low stellar densities. Their formation and evolution remain poorly constrained due to the challenges of detecting their faint disks. We present deep, multi-band optical imaging of Malin 2, a prototypical GLSB galaxy, with the newly commissioned Two-meter Twin Telescope (TTT) at the Teide Observatory. Our $g$, $r$, and $i$-band data reach surface brightness depths of 30.3, 29.5, and 28.2 mag arcsec$^{-2}$ (3$\sigma$, $10^{\prime\prime} \times 10^{\prime\prime}$), tracing the stellar disk of Malin 2 to $\sim$110 kpc. We detect new diffuse structures, including a prominent emission in the northwest coincident with the HI distribution, and a faint spiral arm-like feature in the southeast. We also identify a very faint dwarf galaxy, TTT-d1 ($\mu_{0,g} \sim 26$ mag arcsec$^{-2}$), about 130 kpc southeast of Malin 2, possibly its first known satellite ultra-diffuse galaxy. A multi-directional wedge photometric analysis of Malin 2 shows strong azimuthal variations in its stellar disk. Compared with nearby spirals and other GLSBs, Malin 2 lies at the extreme end in radial extent and stellar mass surface density. The overlap between the asymmetric stellar emission and a lopsided HI distribution suggests contributions from tidal interactions in the formation of the giant disk of Malin 2. Our results highlight the importance of ultra-deep, wide-field imaging in understanding the structural complexity of giant LSB galaxies. Upcoming surveys such as LSST will be crucial to determine whether the features we observe in Malin 2 are common to other giant LSB disk galaxies.

This proceeding presents recent results from a joint analysis of time-dependent neutrino and electromagnetic emissions from tidal disruption events (TDEs), using both isotropic wind models and relativistic jets. We discuss constraints from Fermi Large Area Telescope (LAT) $\gamma$-ray upper limits on the size of the radiation zone and the maximum energies of accelerated cosmic rays, as well as the resulting neutrino productions from TDEs and candidates, including AT 2019dsg, AT 2019fdr, AT 2019aalc, and AT 2021lwx. The Fermi upper limits correspond to a generic neutrino detection rate of $\lesssim0.01-0.1$ per TDE. Additionally, we explore multi-wavelength modeling of jetted TDEs with luminous X-ray afterglows, another TDE subclass, by incorporating the dynamics of structured jets with time-dependent energy injection. We also examine the connection between neutrinos and their multi-wavelength counterparts, highlighting implications for future multi-messenger discoveries with IceCube, IceCube-Gen2, KM3NeT, and Fermi-LAT.

One prominent model for quasi-periodic eruptions (QPEs) is that they originate from extreme mass-ratio inspirals (EMRIs) involving stellar-mass objects orbiting around massive black holes and colliding with their accretion disks. We compute the gravitational wave signals from such a model, demonstrating that orbiter-disk interactions result in small frequency shifts and high-frequency tails due to the excitation of non-discrete modes. Interestingly, we show that QPE RX J1301.9+2747 could be detectable by future space-based gravitational wave detectors, provided a moderate eccentricity around $0.25$ and a mass exceeding $35\,M_\odot$ for the orbiter. Moreover, based on this QPE model, we show that the signal-to-noise ratio of the gravitational wave signals from QPEs, if detectable, will be sufficiently high to distinguish such systems from vacuum EMRIs and shed light on the origin of QPEs and environments around massive black holes.

Active region NOAA 13842 produced two successive solar flares: an X7.1-class flare on October 1, 2024, and an X9.0-class flare on October 3, 2024. This study continues our previous simulation work that successfully reproduced the X7.1-class solar flare (Matsumoto et al. 2025). In this study, we performed a data-constrained magnetohydrodynamic (MHD) simulation using the nonlinear force-free field (NLFFF) as the initial condition to investigate the X9.0-class solar flare. The NLFFF showed the sheared field lines, resulting in the tether-cutting reconnection, the magnetic flux ropes (MFRs), and eventually led to eruption. The magnetic reconnection during the pre-eruption phase plays a critical role in accelerating the subsequent eruption, which is driven by torus instability and magnetic reconnection. Furthermore, our simulation results are consistent with several observational features associated with the X9.0 flare. This simulation could reproduce diverse phenomena associated with the X9.0 flare, including the tether-cutting reconnection, the flare ribbons and the flare loops, the transverse field enhancement, and the remote brightening away from the flare ribbons. However, the initial trigger, magnetic flux emergence, was inferred from observations rather than explicitly modeled, and future comprehensive simulations should incorporate this mechanism directly.

The bispectrum, being sensitive to non-Gaussianity and mode coupling of cosmological fields induced by non-linear gravitational evolution, serves as a powerful probe for detecting deviations from General Relativity (GR). The signatures of modified gravity in the bispectrum are even more pronounced in redshift space, where anisotropies from peculiar velocities provide unbiased information on higher-order properties of gravity. We investigate the potential of all non-zero angular multipoles $B_l^m$ of redshift space bispectrum across all possible triangle configurations to probe degenerate higher-order scalar tensor (DHOST) theory. We show that the higher-order multipoles of the bispectrum with $l=2,4,6$ are more sensitive to the modifications in gravity than the spherically averaged monopole moment $l=0$. These multipoles demonstrate remarkable sensitivity to the higher-order growth history, which varies across triangle configurations, with acute triangles generally being the most sensitive to modification in GR. The values of various multipoles exhibit opposite signs in modified gravity compared to those predicted in GR, which serves as a robust indicator of the deviation from GR. We demonstrate that, unlike $l=2$ and $4$ multipoles, the $l=6$ multipoles with $m\leq 4$ are not affected by the quadratic bias and second-order tidal bias parameters, emphasising the need to leverage their capabilities in analyses. The $(l=6, m > 4)$ multipoles fail to capture the second-order growth, while all $l=8$ multipoles lack any independent information regarding modified gravity in both linear and nonlinear regimes.

Low-mass objects are ubiquitous in our Galaxy. Their low temperature provides them with complex atmospheres characterised by the presence of strong molecular absorption bands which, together with their faintness, have made their accurate characterisation a great challenge for astronomers over the last decades. M dwarfs account for 75% of the census of stars within 10 pc of the Sun, and their suitability as targets in the search for Earth-like planets has led many research groups to focus on the study of these objects, which is crucial for the understanding of the structure and kinematics of our Galaxy. Very low-mass stars and substellar objects with spectral types M7 or later, including the extended L, T, and Y spectral types, constitute the domain of ultracool dwarfs. The study of these objects, discovered definitively in 1995, is key for understanding the boundary between stellar and substellar objects and promises to experience a quantum leap thanks to the characteristics of new-generation surveys such as Euclid or LSST. Data analysis in the field of observational astronomy has undergone a paradigm shift during the last decades driven by an exponential growth in the volume and complexity of available data. In this revolution, the Virtual Observatory has become a cornerstone providing a system that fosters interoperability between astronomical archives around the world. In response to this growth in data complexity, the astronomical community has increasingly adopted machine learning techniques for the development of scalable, automated solutions. This thesis explores the discovery and characterisation of M dwarfs and ultracool dwarfs, using data-driven approaches supported by Virtual Observatory technologies and protocols. We rely on a variety of machine and deep learning techniques to develop flexible methodologies aimed at advancing our understanding of low-mass objects.

Understanding the role of high-redshift protoclusters in cosmic reionization is essential to unveiling the early stages of structure formation. Using deep imaging and spectroscopy from the James Webb Space Telescope (JWST) JADES Deep Survey in GOODS-South, we identify two prominent protoclusters at z>7 and investigate their environmental properties in comparison to field galaxies. Protocluster members exhibit systematically higher ionizing photon production efficiency ($\xi_{\text{ion}}$) and inflated [OIII]/H$\beta$ ratios at fixed UV magnitude or stellar mass, likely driven by young, metal-poor stellar populations and intense star formation. Despite these properties, their Ly$\alpha$ emission is weak or absent, and they show high proximate neutral hydrogen column densities, suggesting insufficient ionizing output to maintain ionized bubbles. We also find that a strong Ly$\alpha$ emitter (LAE), JADES-GS-z7-LA, may lie within the same ionized region as one protocluster. Although their Lyman continuum escape fractions ($f_{\mathrm{esc}} \sim 0.1$) are comparable to those of LAEs, individual protocluster galaxies are faint ($M_{\mathrm{UV}} > -19$) and low-mass ($\log(M_*/M_\odot) \sim 8.5$). The enhanced number density within protoclusters boosts the local UV luminosity density by nearly 1 dex. The surrounding gas remains largely neutral, suggesting that reionization was highly patchy and modulated by environment. The protocluster galaxies likely host ionization-bounded nebulae with holes, suppressing Ly$\alpha$ visibility, in contrast to field galaxies that are more consistent with density-bounded nebulae.

With the knowledge and statistical precision derived from two decades of measurement, the Pierre Auger Observatory has significantly deepened our understanding of ultra-high-energy cosmic rays while unearthing an increasingly complex astrophysical landscape and exposing tensions with hadronic interaction models. The field now demands the mass of individual cosmic-ray primaries as an observable with an exposure that only the 3000-square-kilometer surface array of the Observatory can provide. Access to the primary mass hinges on the disentanglement of the electromagnetic and muonic components of extensive air showers. To achieve this, scintillator and radio detectors have been installed atop each existing water-Cherenkov detector of the surface array, whose dynamic range has also been enhanced through the installation of small-area PMTs. Additionally, the timing and signal resolution of all detector stations have been improved through upgraded station electronics, and underground muon counters have been installed in a region of the array with denser spacing. As the commissioning of the final components of AugerPrime reaches its conclusion and the enhanced array comes fully online, we present the realization of its design, its performance, and the first results from this now multi-hybrid observatory.

Over the past two decades, thousands of confirmed exoplanets have been detected. The next major challenge is to characterize these other worlds and their stellar systems. Much information on the composition and formation of exoplanets and circumstellar debris disks can only be achieved via direct imaging. Direct imaging is challenging because of the small angular separations (< 1 arcsec) and high star-to-planet flux ratios such as ~1e9 for a Jupiter analog or ~1e10 for an Earth analog in the visible. Atmospheric turbulence prohibits reaching such high flux ratios on the ground, so observations must be made above the Earth's atmosphere. The Nancy Grace Roman Space Telescope (Roman), planned to launch in late 2026, will be the first space-based observatory to demonstrate high-contrast imaging with active wavefront control using its Coronagraph Instrument. The instrument's main purpose is to mature the various technologies needed for a future flagship mission to image and characterize Earth-like exoplanets. These technologies include two high-actuator-count deformable mirrors, photon-counting detectors, two complementary wavefront sensing and control loops, and two different coronagraph types. In this paper, we describe the complete set of flight masks in the Roman Coronagraph Instrument, their intended combinations, and how they were laid out, fabricated, and measured.

In the present article, we propose a very simple parametrization of the Hubble function without parametrizing the dark components of the Universe. One of the novelties of the parametrization is that it may include a wide variety of the cosmological models, such as dark energy (both noninteracting and interacting fluids), modified gravity, cosmological matter creation and other known scenarios. The model is constrained with the latest astronomical probes from Hubble parameter measurements, three distinct versions of Type Ia Supernovae (Pantheon+, DESY5, Union3) and baryon acoustic oscillations from Sloan Digital Sky Survey and Dark Energy Spectroscopic Instrument data releases 1 and 2. Our results suggest a mild deviation from the standard $\Lambda$CDM cosmological model for most of the combined datasets. We also find that our model is thermodynamically consistent and performs well in the model comparison tests.

Differential rotation is a key driver of magnetic activity and dynamo processes in the Sun and other stars, especially as the rate differs across the solar layers, but also in active regions. We aim to accurately quantify the velocity at which round {\alpha}-spots traverse the solar disk as a function of their latitude, and compare these rates to those of the quiet-Sun and other sunspot types. We then extend this work to other stars and investigate how differential rotation affects the modulation of stellar light curves by introducing a generalized stellar differential rotation law. We manually identify and track 105 {\alpha}-sunspots in the 6173 {\AA} continuum using the Helioseismic and Magnetic Imager (HMI) aboard the Solar Dynamics Observatory (SDO). We measure the angular velocities of each spot through center-of-mass and geometric ellipse-fitting methods to derive a differential rotation law for round {\alpha}-sunspots. Results. Using over a decade of HMI data we derive a differential rotation law for {\alpha}-sunspots. When compared to previous measurements we find that {\alpha}-sunspots rotate 1.56% faster than the surrounding quiet-Sun, but 1.35% slower than the average sunspot population. This supports the hypothesis that the depth at which flux tubes are anchored influences sunspot motions across the solar disk. We extend this analysis to other stars by introducing a scaling law based on the rotation rates of these stars. This scaling law is implemented into the Stellar Activity Grid for Exoplanets (SAGE) code to illustrate how differential rotation alters the photometric modulation of active stars. Our findings emphasize the necessity of considering differential rotation effects when modeling stellar activity and exoplanet transit signatures

We describe the numerical algorithms of a global magnetohydrodynamic (MHD) code utilizing the Yin-Yang grid, called the Yin-Yang Magnetic Flux Eruption (Yin-Yang-MFE) code, suitable for modeling the large-scale dynamical processes of the solar corona and the solar wind. It is a single-fluid MHD code taking into account the non-adiabatic effects of the solar corona, including the electron heat conduction, optically thin radiative cooling, and empirical coronal heating. We describe the numerical algorithms used to solve the set of MHD equations (with the semi-relativistic correction, or the Boris correction) in each of the partial spherical shell Yin Yang domains, and the method for updating the boundary conditions in the ghost-zones of the two overlapping domains with the code parallelized with the message passing interface (MPI). We validate the code performance with a set of standard test problems, and finally present a solar wind solution with a dipolar magnetic flux distribution at the solar surface, representative of solar minimum configuration.

Turbulent coronae of supermassive black holes can accelerate non-thermal particles to high energies and produce observable radiation, but capturing this process is challenging due to comparable timescales of acceleration, cooling, and the development of cascades. We present a time-dependent numerical framework that self-consistently couples proton acceleration -- modeled by the Fokker-Planck equation -- with leptonic-hadronic radiation. For the neutrino-emitting Seyfert galaxy NGC 1068, we reproduce the neutrino spectrum observed by IceCube, while satisfying gamma-ray constraints. We also consider a transient corona scenario, potentially emerging in non-jetted tidal disruption events like AT 2019dsg, and show that early-stage cascade feedback can impact proton acceleration and radiation processes in weaker coronae, producing delayed optical/ultraviolet, X-ray, and neutrino emissions of $\mathcal O(100~\rm d)$. This flexible code efficiently models multi-messenger signals from both steady and transient astrophysical sources, providing insights in combining particle acceleration and radiation mechanisms.

We study the imprint of magnetic fields on gravitational waves emitted during the inspiral phase of eccentric binary neutron star systems. While observations indicate that neutron stars typically exhibit strong magnetic fields in the range of $10^{14}$-$10^{15}\,\mathrm{G}$, theoretical models allow for fields as high as $ \sim 10^{17-18}\,\mathrm{G}$. In binaries, the fate of these fields depends on the formation pathway: in systems formed through isolated evolution, magnetic fields may decay over long inspiral timescales. In contrast, binaries formed via dynamical capture can retain substantial eccentricity and strong fields until merger, potentially altering the gravitational waveform. We consider two magnetic effects: magnetic interaction between the neutron stars and electromagnetic radiation from the system's effective dipole, and identify regimes where each dominates. Using a perturbative framework, we compute the associated energy loss and gravitational wave phase evolution. We find that for binaries with strong and comparable magnetic fields, $10^{14}\,\mathrm{G}$ fields may be detectable up to $\sim 10 \, \mathrm{Mpc}$ with DECIGO and the Einstein Telescope, while $10^{15}\,\mathrm{G}$ fields extend the reach to several hundred Mpc. For extreme fields of $10^{16}\,\mathrm{G}$, third-generation detectors could be sensitive out to Gpc scales. In contrast, LIGO is limited to galactic distances: $10^{15}\,\mathrm{G}$ fields are detectable only within $\sim 100\,\mathrm{kpc}$, and only ultrastrong fields ($\sim 10^{16}$-$10^{17}\,\mathrm{G}$) are potentially observable at Gpc distances. In highly asymmetric systems, where dipole radiation dominates, the gravitational wave dephasing is significantly suppressed, reducing the detection horizon. These findings suggest that current and future gravitational wave observatories may be capable of identifying magnetized binary systems.

Systematic effects that limit the achievable sensitivity of current low-frequency radio telescopes to the 21-cm signal are among the foremost challenges in observational 21-cm cosmology. The standard approach to retrieving the 21-cm signal from radio interferometric data separates it from bright astrophysical foregrounds by exploiting their spectrally smooth nature, in contrast to the finer spectral structure of the 21-cm signal. Contaminants exhibiting rapid frequency fluctuations, on the other hand, are difficult to separate from the 21-cm signal using standard techniques, and the power from these contaminants contributes to low-level systematics that can limit our ability to detect the 21-cm signal. Many of these low-level systematics are incoherent across multiple nights of observation, resulting in an incoherent excess variance above the thermal noise sensitivity of the instrument. In this paper, we develop a method called cross-GPR (cross covariance Gaussian process regression) that exploits the incoherence of these systematics to separate them from the 21-cm signal, which remains coherent across multiple nights of observation. We first develop and demonstrate the technique on synthetic signals in a general setting, and then apply it to gridded interferometric visibility cubes. We perform realistic simulations of visibility cubes containing foregrounds, 21-cm signal, noise, and incoherent systematics. The simulations show that the method can successfully separate and subtract incoherent contributions to the excess variance, and its advantages over standard techniques become more evident when the spectral behavior of the contaminants resembles that of the 21-cm signal. Simulations performed on a variety of 21-cm signal shapes also reveal that the cross-GPR approach can subtract incoherent contributions to the excess variance, without suppressing the 21-cm signal.

We show that primordial black holes (PBHs) in the $\textit{Stupendously Large Black Hole}$ mass range ($M \gtrsim 10^{11}\,M_\odot$) produce isocurvature perturbations exceeding current $\textit{Planck}$ Cosmic Microwave Background limits, thereby excluding them as a significant dark matter component.

This study investigates the sensitivity of the radio interferometers to identify imprints of spatially inhomogeneous dark matter annihilation signatures in the 21-cm signal during the pre-reionization era. We focus on the upcoming low-mode survey of the Square Kilometre Array (SKA-Low) telescope. Using CNNs, we analyze simulated 3D 21-cm differential brightness temperature maps generated via the DM21cm code, which is based on 21cmFAST and DarkHistory, to distinguish between spatially homogeneous and inhomogeneous energy injection/deposition scenarios arising from dark matter annihilation. The inhomogeneous case accounts for local dark matter density contrasts and gas properties, such as thermal and ionization states, while the homogeneous model assumes uniform energy deposition. Our study focuses on two primary annihilation channels to electron-positron pairs ($e^+e^-$) and photons ( $\gamma \gamma$), exploring dark matter masses from 1 MeV to 100 MeV and a range of annihilation cross-sections. For $\gamma \gamma$ channel, the distinction across dark matter models is less pronounced due to the larger mean free path of the emitted photons, resulting in a more uniform energy deposition. For $e^+e^-$ channel, the results indicate that the CNNs can effectively differentiate between the inhomogeneous and homogeneous cases. Despite observational challenges, the results demonstrate that these effects remain detectable even after incorporating noise from next-generation radio interferometers, such as the SKA. We find that the inhomogeneous dark matter annihilation models can leave measurable imprints on the 21-cm signal maps distinguishable from the homogeneous scenarios for the dark matter masses $m_{\rm DM}=1$ MeV and the annihilation cross-sections of $\geq 5 \times 10^{-30}~{\rm cm^3/sec}$ ($\geq 5 \times 10^{-29}~{\rm cm^3/sec}$ for $m_{\rm DM}=100$ MeV) for moderate SKA-Low noise.

Answering the question "do rocky exoplanets around M stars have atmospheres?" is a key science goal of the JWST mission, with 500 hours of Director's Discretionary Time (DDT) awarded to address it. Theoretically, the so-called "Cosmic Shoreline" may not hold around M stars due to their harsher XUV environment, possibly resulting in most rocky planets lacking significant atmospheres -- a hypothesis that remains to be statistically tested through judicious target selection. We identify target selection as a combinatorial optimization problem ("knapsack problem"). We develop a statistical framework to test population-level hypotheses from observations and combine a formation and evolution model, 1D-RCE atmosphere model, and genetic algorithm to simulate populations and find the optimal set of observations. We find that, firstly, if all rocky planets around M stars are indeed bare rocks, JWST can efficiently place an upper bound on the atmosphere occurrence rates to less than 1 in 8, even without optimized target selection, but further improvements to the constraint are cost-prohibitive. Secondly, if the Cosmic Shoreline hypothesis (XUV or bolometric) holds true for M stars, strong evidence ($\Delta$BIC>5) can be found within ~500 observing hours using the optimal strategy of a "wide and shallow" approach. Our statistical framework can be directly applied to upcoming observations to robustly identify the Cosmic Shoreline and to optimize target selection for determining other trends in exoplanet atmosphere observations, including those from future missions.