Sazuna/UAT_keywords huggingface dataset:
Deciphering Profile Stability in Millisecond Pulsars: Timescales, Frequency Evolution, and Implications on Emission Mechanisms. Pulse profile stability in millisecond pulsars (MSPs) is a key factor in achieving high-precision timing essential for detecting nanohertz gravitational waves with pulsar timing arrays (PTAs). In this work, we present a systematic analysis of profile stabilization timescales in MSPs using a direct method based on pulse stacking, applied to long-term multiepoch observations. Our study utilizes data from the upgraded Giant Metrewave Radio Telescope (uGMRT) between 300 and 750 MHz for nine MSPs over 3─5 yr and Parkes Ultra-Wideband, low-frequency receiver observations (covering 704─4032 MHz) for three of them. We find that stable profiles typically require averaging over 105─106 pulses. This is the first time such a quantitative approach has been applied to MSPs across a wide frequency range, providing an indirect but practical estimate of jitter noise—a dominant noise source in PTA data sets. We observe that stabilization timescales depend on signal-to-noise ratio, pulse morphology, and surface magnetic field strength, with a moderate correlation indicating a possible role of magnetic field in emission stability. A complementary single-epoch analysis of nine bright MSPs with uGMRT Band-3 (300─500 MHz) reinforces these results and demonstrates the method's applicability to broader MSP populations. We show that a strong correlation exists between profile-stability slope and the jitter parameter, implying that, for faint MSPs, profile-stability analysis can act as an effective proxy for intrinsic pulse-shape variability. Our work provides a novel and scalable framework to assess intrinsic profile variability, helping to guide integration time choices and reduce timing noise in PTA experiments.

Keywords: Neutron stars, Pulsars, Millisecond pulsars
Verification of Cas A Neutron Star Cooling Rate Using Chandra HRC-S Observations. The young neutron star (NS) in the Cassiopeia A (Cas A) supernova remnant is a fascinating test for theories of NS cooling. Chandra observations have indicated that its surface temperature is declining rapidly, by about 2% per decade, using 20 yr of data, if a uniform carbon atmosphere is assumed for the NS. This rapid decline may be caused by the neutrons in the NS core transitioning from a normal to a superfluid state. However, most of the Cas A NS observations were performed by the Chandra ACIS detectors, which suffer complicated systematic effects. Here, we test the cooling of the Cas A NS with Chandra High Resolution Camera (HRC) data over 25 yr. The Chandra HRC detector has independent systematics, serving as a cross-check. Assuming a fixed hydrogen column density (NH ), we infer the cooling rate of the Cas A NS to be 0.57 −0.27+0.26 % per decade. Allowing the NH to vary with time (as estimated using ACIS data), the cooling rate is 1.11 −0.28+0.25 % per decade. These cooling rates are smaller than measured using ACIS data, implying systematic uncertainties have not been eradicated from either or both data sets. However, we have verified the decline in the absorbed flux from the Cas A NS using an independent instrument, at &gt;3σ level (4.7% ± 1.5% over 10 yr). Additionally, the weaker cooling rate of Cas A NS inferred from HRC data sets eliminates the tension with the theoretically predicted cooling, and can be explained by the reduced efficiency of the neutrino emission accompanying the Cooper pair breaking and formation process in neutron triplet-state superfluid.

Keywords: Neutron stars, Supernova remnants, X-ray astronomy
On the Variability Features of Active Galactic Nuclei in Little Red Dots. The high-redshift (z &gt; 4) compact sources with "V-shaped" spectral energy distributions, known as Little Red Dots (LRDs), were discovered by the James Webb Space Telescope and provide valuable clues to the physics of active galactic nuclei (AGNs) in the early Universe. The nature of LRDs is controversial. Recently, several studies have investigated LRDs through variability, a characteristic feature of AGNs. These studies explore LRD variability by extrapolating empirical relationships from local quasars. Here, we adopt the Corona-heated Accretion-disk Reprocessing (CHAR) model, which is motivated by accretion physics and is applicable to reproducing AGN conventional variability, to study the variability of 22 LRDs in W. L. Tee et al. Our results indicate that the observed variability in LRDs is dominated by measurement uncertainties. Within the CHAR model, the lack of variability in LRDs can be explained by two scenarios: either AGNs contribute ≲30% of the observed luminosities, or they are intrinsically luminous AGNs. We use simulations to demonstrate the observational requirements to effectively investigate LRDs via variability with the following criteria: first, the sample has about 200 LRDs; second, each LRD has two observations separated by at least 2 yr in the observed frame; third, the photometric uncertainty is ≤0.07 mag. If the LRDs still lack variability under these conditions, the time─domain study would provide independent evidence that the accretion mode of LRDs differs significantly from low-redshift quasars.

Keywords: Accretion, Supermassive black holes, Active galactic nuclei, High-redshift galaxies
Mapping Feedback Signatures in 3C 297: A Quasar-host Merger at Cosmic Noon. We present a study of quasar host galaxy 3C 297, which is home to a powerful bent-jet radio source suggesting vigorous interaction with a dense interstellar medium (ISM) and/or jet precession. Archival Hubble Space Telescope (HST) imaging showed interestingly perturbed morphology of the host with a bright ∼30 kpc arc feature, extended filamentary structure of line-emitting gas, and clumpy blue excess emission cospatial with the radio hotspots. Our Very Large Telescope (VLA)/SINFONI integral-field observations reveal complex, spatially resolved Hα + [N II] emission in this source. A prominent blueshifted wing in Hα indicates an ionized gas flow extending out to ∼8 kpc from the nuclear region. Combining our SINFONI narrow-Hα data with archival HST/UV and VLA imaging, we map the young stellar population in the host and compare the spatial distribution of star-forming regions with the ionized gas motion and jet structure. In the attempt to characterize the feedback mechanisms in this chaotic system, we suggest that the powerful radio source dominates the feedback, with possible contribution from radiation pressure due to accretion onto the black hole. We also propose that the expanding jet cocoon likely shocked the ISM, triggering a kpc-scale ionized gas outflow and new starbursts that enhanced ongoing merger-induced star formation.

Keywords: AGN host galaxies, Radio galaxies, Active galactic nuclei, Quasars
Inside-out versus Upside-down: The Origin and Evolution of Metallicity Radial Gradients in FIRE Simulations of Milky Way-mass Galaxies and the Essential Role of Gas Mixing. Within the Milky Way (MW), younger stellar populations exhibit steeper (more negative) metallicity radial gradients; the origin of this trend remains debated. The FIRE-2 cosmological simulations of MW-mass galaxies show the same trend as the MW, which in FIRE-2 arises because the metallicity gradient of the interstellar medium (ISM), and thus of stars at birth, became steeper over time. We seek to understand this evolution in the context of inside-out radial growth of galaxies. Most FIRE-2 galaxies grew radially from the inside out in both gas and stars; specifically, their surface density profiles, Σ(R), became shallower over time. Combined with a realized superlinear (Kennicutt–Schmidt-like) relation between star formation and total gas density, the profile of the ratio Σstar(R)/Σgas(R) became shallower (flatter) over time. Thus, if metals stayed where they were injected into the ISM from stars, the metallicity gradient would become shallower over time, as some models predict. However, metallicity gradients in FIRE-2 became steeper over time because of the additional effects of (radial) mixing of metals in the ISM. Specifically, the velocity dispersion and net radial advection of gas declined over time, as ISM turbulence decreased and the disk settled, leading to upside-down vertical growth. In FIRE-2, this evolution in metal mixing of gas associated with upside-down growth dominates over inside-out radial growth, causing the metallicity radial gradient of the ISM and of stars at birth to become steeper over time. We argue that this reflects the ISM history of typical MW-mass galaxies and a plausible history of the MW.

Keywords: Galaxy chemical evolution, Chemical abundances, Galaxy evolution, Milky Way evolution, Astronomical simulations
A Multilayer Perceptron to Extend and Improve Diatomic Molecule Collision Rate Coefficients. A data-driven approach to improve the accuracy of state-resolved molecular collision data for the relaxation of vibrationally and rotationally excited molecules is developed. We apply the approach to the SiO─H2 collision system, which is crucial for reliable astrophysical environment modeling of SiO emission. The most accurate quantum scattering calculation method employs the coupled-channel formalism, which is computationally expensive. Approximate approaches, generally referred to as decoupling approximations, are significantly more computationally efficient, but less accurate. To bridge this accuracy gap, we use a multilayer perceptron to predict the difference between the accurate and approximate results. Our model is trained on a carefully selected and preprocessed data set, which includes both approximate and accurate calculation results. We show that our approach significantly improves the accuracy of the approximate calculation results, as the relative rms errors from the predicted results are orders of magnitude smaller than those from the approximate calculation results, benchmarked against the accurate calculations. The present approach can be applied to similar problems in other fields to improve the accuracy of computationally efficient approximate methods, reducing computation time and enhancing automation.

Keywords: Interstellar molecules, Atomic physics, Neural networks, Molecular physics, Interstellar medium, Interstellar scattering
Glimmers in the Cosmic Dawn. II. A Variability Census of Supermassive Black Holes across the Universe. Understanding the origin and evolution of supermassive black holes (SMBHs) stands as one of the most important challenges in astrophysics and cosmology, with little current theoretical consensus. Improved observational constraints on the cosmological evolution of SMBH demographics are needed. Here we report results of a search via photometric variability for SMBHs appearing as active galactic nuclei (AGN) in the cosmological volume defined by the Hubble Ultra Deep Field. This work includes particular focus on a new observation carried out in 2023 with the Hubble Space Telescope using the WFC3/IR/F140W, which is compared directly to equivalent data taken 11 yr earlier in 2012. Two earlier pairs of observations from 2009 to 2012 with WFC3/IR/F105W and WFC3/IR/F160W are also analyzed. We identify 521, 188, and 109 AGN candidates as nuclear sources that exhibit photometric variability at a level of 2σ, 2.5σ, and 3σ, respectively, in at least one filter. This sample includes 13, 3, and 2 AGN candidates at redshifts z &gt; 6, when the Universe was ≲900 Myr old. After variability and luminosity function (down to MUV = −17 mag) completeness corrections, we estimate the comoving number density of SMBHs, nSMBH(z). At z ≳ 6, nSMBH ≳ 6 × 10−3 cMpc−3. At low z our observations are sensitive to AGN fainter than MUV = −17 mag, and we estimate nSMBH ≳ 10−2 cMpc−3. We discuss how these results place strong constraints on a variety of SMBH seeding theories. *This research is based on observations made with the NASA/ESA Hubble Space Telescope obtained from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5─26555. These observations are associated with programs 1563, 12498, and 17073.

Keywords: Supermassive black holes, Active galactic nuclei, High-redshift galaxies, Galaxies
The z ∼ 1.03 Merging Cluster SPT-CL J0356─5337: New Strong Lensing Analysis with HST and MUSE. We present a strong lensing analysis and reconstruct the mass distribution of SPT-CL J0356−5337, a galaxy cluster at redshift z = 1.034. Our model supersedes previous models by making use of new multiband Hubble Space Telescope data and Multi-Unit Spectroscopic Explorer (MUSE) spectroscopy. We identify two additional lensed galaxies to inform a more well-constrained model using 12 sets of multiple images in five separate lensed sources. The three previously known sources were spectroscopically confirmed by G. Mahler et al. at redshifts of z = 2.363, z = 2.364, and z = 3.048. We measured the spectroscopic redshifts of two of the newly discovered arcs using MUSE data, at z = 3.0205 and z = 5.3288. We increase the number of cluster member galaxies by a factor of 3 compared to previous work. We also report the detection of extended Lyα emission from several background galaxies. We measure the total projected mass density of the two major subcluster components, one dominated by the brightest cluster galaxy and the other by a compact group of luminous red galaxies. We find  MBCG(&lt;80kpc)=3.93−0.14+0.21×1013  M⊙ and  MLRG(&lt;80kpc)=2.92−0.23+0.16×1013  M⊙, yielding a mass ratio of  1.35−0.08+0.16 . The strong lensing constraints offer a robust estimate of the projected mass density regardless of modeling assumptions; allowing more substructure in this line of sight does not change the results or conclusions. Our results corroborate the conclusion that SPT-CL J0356−5337 is dominated by two mass components and is likely undergoing a major merger on the plane of the sky.

Keywords: Galaxy clusters, Cosmology, High-redshift galaxy clusters, Strong gravitational lensing, Gravitational lensing, Lyman-alpha galaxies, Dark matter
Modeling the Reverberation Response of the Broad-line Region in Active Galactic Nuclei. II. Incorporating Photoionization Models. The broad emission lines (BELs) emitted by active galactic nuclei respond to variations in the ionizing continuum emission from the accretion disk surrounding the central supermassive black hole (SMBH). This reverberation response provides insights into the structure and dynamics of the broad-line region (BLR). In 2024, we introduced a new forward-modeling tool, the Broad Emission Line Mapping Code (BELMAC), which simulates the velocity-resolved reverberation response of the BLR to an input light curve. In this work, we describe a new version of BELMAC, which uses photoionization models to calculate the cloud luminosities for selected BELs. We investigated the reverberation responses of Hα, Hβ, Mg II λ2800, and C IV λ1550 for models representing a disk-like BLR with Keplerian rotation, radiatively driven outflows, and inflows. The line responses generally provide a good indication of the respective luminosity-weighted radii. However, there are situations where the BLR exhibits a negative response to the driving continuum, causing overestimates of the luminosity-weighted radius. The virial mass derived from the models can differ dramatically from the actual SMBH mass, depending mainly on the disk inclination and velocity field. In single-zone models, the BELs exhibit similar responses and profile shapes; two-zone models, such as a Keplerian disk and a biconical outflow, can reproduce observed differences between high- and low-ionization lines. Radial flows produce asymmetric line profile shapes due to both anisotropic cloud emission and electron scattering in an intercloud medium. These competing attenuation effects complicate the interpretation of profile asymmetries.

Keywords: Supermassive black holes, Reverberation mapping, Astronomy data modeling, Active galactic nuclei
Flat Tails in Fast Radio Burst and Pulsar Energy Distributions: Implications for Optimizing Nearby Fast Radio Burst Surveys. Fast radio bursts (FRBs) are energetic, short-duration radio pulses of unclear origin. To explore effective survey strategies for detecting FRBs from nearby globular clusters (GCs), we investigate the burst energy distribution, which has a strong influence on the detection rate. We reanalyze FRBs and pulsars exhibiting broad energy distributions by fitting their high-energy tails with power-law models. Two cosmological repeating FRBs (FRB 20201124A and FRB 20220912A), one nearby FRB (FRB 20200120E), and two pulsars (RRATs J1846‑0257 and J1854+0306) exhibit power-law indices of α ≳ ‑1, suggesting that their bright pulses contribute significantly to the total radio pulse energy. The brightest bursts from these sources can be fitted with a power-law model (αBri = ‑0.26 ± 0.05), suggesting that an extremely flat index is required to naturally derive high-luminosity FRBs from low-luminosity sources. We present detailed survey strategies for FAST, MeerKAT, and Parkes cryoPAF in the search for FRBs in nearby GCs using different power-law indices, recommending targets for observation. We suggest that combining observations with FAST (∼3 hr) and Parkes cryoPAF (10‑20 hr) is practicable for discovering new FRBs in nearby GCs.

Keywords: Radio bursts, Radio pulsars, Radio transient sources
Reconstruction of X-Ray Afterglow Light Curves of Gamma-Ray Bursts and Its Implication on Constraining Cosmological Parameters. Gamma-ray bursts (GRBs) serve as important cosmological probes whose X-ray afterglow light curves (LCs) may exhibit a plateau phase (with temporal slope α between 0 and 0.5) that may originate from magnetar energy injection. Similar to Type Ia supernovae, GRBs with a common physical origin can be used as standardizable candles for cosmological studies. However, observational gaps in GRB LCs introduce significant uncertainties in plateau parameter estimation, thereby affecting cosmological constraints. In this work, we employ a stochastic reconstruction technique to reconstruct the X-ray afterglow LCs for 35 GRB samples exhibiting plateau features, generating 50 simulated data points for each LC. Using the reconstructed LCs, we calibrate three luminosity correlations: the L0–tb, L0–tb–Ep,i, and L0–tb–Eγ,iso relations, which are then applied to constrain both flat and nonflat ΛCDM cosmological models. The main results include (i) the L0–tb relation yields a slope b ≈ ‑1, supporting a constant magnetar energy injection rate; (ii) LC reconstruction has limited impact on cosmological parameter constraints; and (iii) for the flat ΛCDM model constrained by the L0–tb–Ep,i relation, the precision of Ωm improves by 6.25%; for the non-flat ΛCDM model constrained by the L0–tb–Ep,i relation, the precision of ΩΛ improves by 1.01%. Our findings suggest that increasing the number of LC data points provides limited improvement to cosmological constraints, while expanding the sample size of GRBs with identical physical origins may be more crucial.

Keywords: Cosmology, Magnetars, Gamma-ray bursts
Mass Segregation and Transient Formation in Nuclear Stellar Clusters. Supermassive black holes at the centers of galaxies occasionally disrupt stars or consume stellar-mass black holes (BHs) that wander too close, producing observable electromagnetic or gravitational wave signals. We examine how mass segregation impacts the rates and distributions of such events. Assuming a relaxed stellar cluster, composed of stars and stellar-mass BHs, we show that the tidal disruption rate of massive stars (m ≳ M⊙) is enhanced relative to their abundance in the stellar population. For stars up to m ≈ 3M⊙, this enhancement is roughly m/M⊙ and it is driven by segregation within the sphere of influence. Stars with masses m ≳ 3M⊙, if relaxed, are predominantly scattered by more massive stellar-mass BHs, leading to a constant enhancement factor of ≈9, independent of mass. This aligns with observational evidence suggesting an over-representation of massive stars in tidal disruption events. For stellar-mass BHs, we predict an enhancement factor scaling as  m•1/2  for plunges and  m•3/2  for extreme-mass-ratio inspirals (EMRIs). The power of one-half in both cases reflects the shorter relaxation times of heavier BHs, allowing them to segregate into the sphere of influence from greater distances, thereby increasing their abundance. The additional power in the EMRIs' rate arises from the tendency of heavier BHs to circularize and sink inward more efficiently. Finally, we estimate the rate of main-sequence star inspirals and find that it favors low-mass stars (m ≲ M⊙). This seems compatible with the observationally estimated rate of quasiperiodic eruptions.

Keywords: Supermassive black holes, Galactic center, Tidal disruption, Stellar dynamics, Gravitational wave sources, X-ray transient sources
QPEs from EMRI Debris Streams Impacting Accretion Disks in Galactic Nuclei. Quasi-periodic eruption (QPE) sources in galactic nuclei are often associated with a stellar object orbiting a supermassive black hole with an hours to days period, which is brought in as an extreme mass-ratio inspiral (EMRI). In the presence of an accretion disk, repeated star─disk collisions lead to ablation of a small fraction of the stellar mass during each disk passage. We analytically track stellar debris as it is tidally stretched outside the EMRI's Hill sphere, forming an elongated, dilute stream that collides with the disk half an orbit after the last star─disk encounter. For orbital periods ≳12 hr, the dilute stream is deflected at the disk surface by a strong shock, rather than penetrating it. Due to their low optical depth and prolonged interaction time, radiation from the shocked streams typically dominates over emission from shocked disk gas directly impacted by the star. We find that (1) QPE flare durations reflect the stream─disk collision timescale; (2) flare luminosities of 1042−43 erg s−1, consistent with observed QPEs, are robustly produced; (3) soft X-ray flares with temperatures of ∼100 eV arise when the stream mass is sufficient to sustain a radiation-mediated shock at the collision interface. Higher-mass streams yield softer flares, typically outshone by the disk, while lower-mass streams result in collisionless shocks, which likely produce fainter and harder flares. We discuss observational implications of the temporal evolution of the underlying disk, assuming it is the remnant of a prior tidal disruption event in the same galaxy.

Keywords: Accretion, Supermassive black holes, Tidal disruption, X-ray transient sources, Shocks
A Common Origin of Normal Type Ia Supernovae Suggested by the Photometric Diversity. In recent years, with the increasing number of type Ia supernovae (SNe Ia) discovered soon after their explosions, a nonnegligible fraction of SNe Ia with early-excess emissions (EExSNe Ia) have been confirmed. In this paper, we present a total of 67 early-phase normal SNe Ia from published papers and ongoing transient survey projects to systematically investigate their photometric behaviors from very early time. We found that EExSNe Ia in our sample have longer rise and brighter peak luminosities compared to non-EExSNe Ia. Moreover, EExSNe Ia commonly have "tiny red bump" or "blue plateau" features in the early B − V color while non-EExSNe Ia show blueward evolution from the very beginning. Here, we propose that the thin He-shell double detonation scenario can phenomenologically explain the photometric diversities of normal SNe Ia considering different white dwarf─He-shell mass combinations and the viewing angle effect, implying a unified explosion mechanism of normal-type SNe Ia. To further verify the possible common origin of normal SNe Ia, systematical studies of multiband photometric and spectral properties of early-phase SNe Ia through the new-generation wide-field time-domain survey facilities and global real-time follow-up networks are highly needed.

Keywords: Transient sources, Type Ia supernovae, Supernovae