Sazuna/UAT_keywords huggingface dataset:
Core States of Neutron Stars from Anatomizing Their Scaled Structure Equations. Given an Equation of State (EOS) for neutron star (NS) matter, there is a unique mass-radius sequence characterized by a maximum mass ${M}_{\mathrm{NS}}^{\max }$ at radius R max. We first show analytically that the ${M}_{\mathrm{NS}}^{\max }$ and R max scale linearly with two different combinations of the NS central pressure P c and energy density ɛ c, by dissecting perturbatively the dimensionless Tolman-Oppenheimer-Volkoff (TOV) equations governing NS internal variables. The scaling relations are then verified via 87 widely used and rather diverse phenomenological as well as 17 microscopic NS EOSs with/without considering hadron-quark phase transitions and hyperons, by solving numerically the original TOV equations. The EOS of the densest NS matter allowed before it collapses into a black hole is then obtained. Using the universal ${M}_{\mathrm{NS}}^{\max }$ and R max scalings and Neutron Star Interior Composition Explorer and XMM-Newton mass-radius observational data for PSR J0740+6620, a very narrow constraining band on the NS central EOS is extracted directly from the data for the first time, without using any specific input EOS model.

Keywords: Neutron star cores
CO Survey of High-z Radio Galaxies, Revisited with the Atacama Large Millimeter/submillimeter Array: Jet-Cloud Alignments and Synchrotron Brightening by Molecular Gas in the Circumgalactic Environment. Powerful radio sources associated with supermassive black holes are among the most luminous objects in the universe, and are frequently recognized both as cosmological probes and active constituents in the evolution of galaxies. We present alignments between radio jets and cold molecular gas in the environment of distant radio galaxies, and show that the brightness of the radio synchrotron source can be enhanced by its interplay with the molecular gas. Our work is based on CO J &gt; 1 observations with the Atacama Large Millimeter/submillimeter Array (ALMA) of three radio galaxies with redshifts in the range 1.4 &lt; z &lt; 2.1, namely MRC 0114-211 (z = 1.41), MRC 0156-252 (z = 2.02), and MRC 2048-272 (z = 2.05). These ALMA observations support previous work that found molecular gas out to 50 kpc in the circumgalactic environment, based on a CO(1-0) survey performed with the Australia Telescope Compact Array. The CO emission is found along the radio axes but beyond the main radio lobes. When compared to a large sample of high-z radio galaxies from the literature, we find that the presence of this cold molecular medium correlates with an increased flux-density ratio of the main versus counter-lobe. This suggest that the radio lobe brightens when encountering cold molecular gas in the environment. While part of the molecular gas is likely related to the interstellar medium from either the host or a companion galaxy, a significant fraction of the molecular gas in these systems shows very low excitation, with r 2-1/1-0 and r 3-2/1-0 values ≲0.2. This could be part of the circumgalactic medium.

Keywords: Radio jets, Galaxy environments, Millimeter astronomy, Protoclusters, Radio astrometry, Radio loud quasars, Radio galaxies, Circumgalactic medium, Submillimeter astronomy, Intracluster medium, Ultraluminous infrared galaxies, High-redshift galaxies
Stellar Collisions in Galactic Nuclei: Impact on Destructive Events Near a Supermassive Black Hole. The centers of galaxies host both a supermassive black hole and a dense stellar cluster. Such an environment should lead to stellar collisions, possibly at very high velocities so that the total energy involved is of the same order as supernova explosions. We present a simplified numerical analysis of the destructive stellar collision rate in a cluster similar to that of the Milky Way. The analysis includes an effective average two-body relaxation Monte Carlo scheme and general relativistic effects, as used by Sari &amp; Fargione, to which we added explicit tracking of local probabilities for stellar collisions. We also consider stars which are injected into the stellar cluster after being disrupted from a binary system by the supermassive black hole. Such stars are captured in the vicinity of the black hole and enhance the expected collision rate. In our results we examine the rate and energetic distribution function of high-velocity stellar collisions, and compare them self-consistently with the other destructive processes which occur in the galactic center, namely tidal disruptions and extreme mass ratio inspirals.

Keywords: Supermassive black holes, Galactic center, Stellar dynamics, Transient sources, Analytical mathematics, Computational methods
Green Bank Telescope Discovery of the Redback Binary Millisecond Pulsar PSR J0212+5321. We report the discovery of a 2.11 ms binary millisecond pulsar during a targeted search of the redback optical candidate coincident with the γ-ray source 3FGL J0212.5+5320 using the Robert C. Byrd Green Bank Telescope (GBT) with the Breakthrough Listen backend at L band. Over a seven month period, five pointings were made near inferior conjunction of the pulsar in its 20.9 hr orbit, resulting in two detections, lasting 12 and 42 minutes. The pulsar dispersion measure (DM) of 25.7 pc cm-3 corresponds to a distance of 1.15 kpc in the NE2001 Galactic electron density model, consistent with the Gaia parallax distance of 1.16 ± 0.03 kpc for the companion star. We suspect the pulsar experiences wide orbital eclipses, similar to other redbacks, as well as scintillation and DM delays caused by its interaction with its companion and surroundings. Although the pulsar was only detected over ≈3.7% of the orbit, its measured acceleration is consistent with published binary parameters from optical radial velocity spectroscopy and light-curve modeling of the companion star, and it provides a more precise mass ratio and a projected semimajor axis for the pulsar orbit. We also obtained a refined optical photometric orbit ephemeris, and observed variability of the tidally distorted companion over 7 yr. A hard X-ray light curve from NuSTAR shows expected orbit-modulated emission from the intrabinary shock. The pulsar parameters and photometric ephemeris greatly restrict the parameter space required to search for a coherent timing solution including pulsar spin-down rate, either using Fermi γ-rays or further radio pulse detections.

Keywords: Neutron stars, Rotation powered pulsars, Millisecond pulsars, Pulsars, Binary pulsars, Radio pulsars
Meterwavelength Single Pulse Polarimetric Emission Survey. VI. Toward Understanding the Phenomenon of Pulsar Polarization in Partially Screened Vacuum Gap Model. We have observed 123 pulsars with periods longer than 0.1 s in the Meterwavelength Single Pulse Polarimetric Emission Survey. In this work, a detailed study of the polarization behavior of these pulsars has been carried out. We were able to fit the rotating vector model to the polarization position angle sweeps in 68 pulsars, and in 34 pulsars the emission heights could be measured. In all cases the radio emission was constrained to arise below 10% of the light cylinder radius. In pulsars with low spin-down energy loss,  Ė&lt;1034  erg s−1, we found the mean fractional linear polarization of the individual time samples in single pulses to be around 0.57 (57%), which is significantly larger than the fractional linear polarization of 0.29 (29%) obtained from the average profiles. On the other hand, the mean fractional circular polarization of the individual time samples in single pulses is around 0.08 (8%), similar to the measurements from the average profiles. To explain the observed polarization features, we invoke the partially screened vacuum gap model of pulsars, where dense spark-associated plasma clouds exist with high pair plasma multiplicity, with significant decrease of density in the regions between the clouds that are dominated by iron ions. The coherent radio emission is excited by curvature radiation from charge bunches in these dense plasma clouds and escape as linearly polarized waves near cloud boundaries. We suggest that the circular polarization arises due to propagation of waves in the low-pair-multiplicity, ion-dominated inter-cloud regions.

Keywords: Radio pulsars
Propagation of Very-high-energy γ-Rays from Distant Blazars. We rederive the possible dependence of the redshift with a very-high-energy (VHE) γ-ray photon index. The results suggest that the universe to VHE γ-rays is becoming more transparent than expected. We introduce the extragalactic background light (EBL) and photon to axion-like particle (ALP) oscillations to explain this phenomenon. We concentrate our analysis on 70 blazars up to redshift z ≃ 1. Assuming this correlation is solely the result of photon-photon absorption of VHE photons with the EBL, with deviations between the predictions and observations, especially at redshifts 0.2 &lt; z &lt; 1. We then discuss the implications of photon-ALP oscillations for the VHE γ-ray spectra of blazars. Strong evidence shows that (1) the results of the EBL attenuation show that the VHE γ-ray photon index increases nonlinearly at the ranges of redshift 0.03 &lt; z &lt; 0.2 and (2) the photon-ALP oscillation results in an attractive characteristic in the VHE γ-ray photon index at the ranges of redshift 0.2 &lt; z &lt; 1. We suggest that both EBL absorption and photon-ALP oscillation can influence the propagation of VHE γ-rays from distant blazars.

Keywords: Blazars, Flat-spectrum radio quasars, BL Lacertae objects
Pitch-angle Distributions of 0.5-1 GeV Solar Protons Crossing Earth's Orbit: Influence of the Large-scale Turbulent Interplanetary Magnetic Field. Using numerical simulations, we analyze the time evolution of the pitch-angle distribution of 500 MeV and 1 GeV solar protons, released impulsively near the Sun, at 1 au. The numerical model solves the equations of motion of an ensemble of particles that move in both the average Parker spiral field and a large-scale turbulent interplanetary magnetic field (IMF). Our model also includes the heliospheric current sheet (HCS). The focus of this study is to determine the effect of the large-scale turbulent IMF on the pitch-angle distribution of GV-rigidity protons and its time variations in terms of understanding variations in ground-level enhancement (GLE) events. Our particular interest is to explain the two distinct opposite-directed fluxes of the unusual event on 1989 October 22 (GLE#44). The results show that by adding the large-scale turbulence to the average Parker IMF, the pitch-angle distribution at 1 au depends strongly on the observer's location relative to the release location of the particles at the Sun. Even a 0.2° displacement in latitude or longitude leads to a significant change in the observed distribution and/or its variation in time. We find that there are some observer locations for which the distinct sunward and antisunward fluxes coexist at certain times of the events. We also find that the HCS has an important effect. For instance, even in locations of poor magnetic connection with the release location at the Sun, but near the HCS, there can be two fluxes moving in different directions at the same time.

Keywords: Solar energetic particles
Energy Repartition and Entropy Generation across the Earth's Bow Shock: MMS Observations. The evolution of plasma entropy and the process of plasma energy redistribution at the collisionless plasma shock front are evaluated based on the high temporal resolution data from the four Magnetospheric Multiscale spacecraft during the crossing of the terrestrial bow shock. The ion distribution function has been separated into the populations with different characteristic behaviors in the vicinity of the shock: the upstream core population, the reflected ions, the gyrating ions, the ions trapped in the vicinity of the shock, and the downstream core population. The values of ion and electron moments (density, bulk velocity, and temperature) have been determined separately for these populations. It is shown that the solar wind core population bulk velocity slows down mainly in the ramp with the electrostatic potential increase but not in the foot region as it was supposed. The reflected ion population determines the foot region properties, so the proton temperature peak in the foot region is an effect of the relative motion of the different ion populations, rather than an actual increase in the thermal speed of any of the ion population. The ion entropy evaluated showed a significant increase across the shock: the enhancement of the ion entropy occurs in the foot of the shock front and at the ramp, where the reflected ions are emerging in addition to the upstream solar wind ions, the anisotropy growing to generate the bursts of ion-scale electrostatic waves. The entropy of electrons across the shock does not show a significant change: electron heating goes almost adiabatically.

Keywords: Solar wind, Planetary bow shocks
Light Curves of Type IIP Supernovae from Neutrino-driven Explosions of Red Supergiants Obtained by a Semianalytic Approach. Type IIP supernovae (SNe IIP) mark the explosive death of red supergiants (RSGs), evolved massive stars with an extended hydrogen envelope. They are the most common supernova type and allow for the benchmarking of supernova explosion models by statistical comparison to observed population properties rather than by comparing individual models and events. We construct a large synthetic set of SNe IIP light curves (LCs) using the radiation hydrodynamics code SNEC and explosion energies and nickel masses obtained from an efficient semianalytic model for two different sets of stellar progenitor models. By direct comparison, we demonstrate that the semianalytic model yields very similar predictions as alternative phenomenological explosion models based on 1D simulations. We find systematic differences of a factor of ~2 in plateau luminosities between the two progenitor sets due to different stellar radii, which highlights the importance of the RSG envelope structure as a major uncertainty in interpreting the LCs of SNe IIP. A comparison to a volume-limited sample of observed SNe IIP shows decent agreement in plateau luminosity, plateau duration, and nickel mass for at least one of the synthetic LC sets. The models, however, do not produce sufficient events with very small nickel mass M Ni &lt; 0.01 M ⊙ and predict an anticorrelation between plateau luminosity and plateau duration that is not present in the observed sample, a result that warrants further study. Our results suggest that a better understanding of RSG stellar structure is no less important for reliably explaining the LCs of SNe IIP than the explosion physics.

Keywords: Core-collapse supernovae, Type II supernovae, Light curves, Radiative transfer simulations, Supernova dynamics
Long-duration Gamma-Ray Burst Progenitors and Magnetar Formation. Millisecond magnetars produced in the center of dying massive stars are one prominent model to power gamma-ray bursts (GRBs). However, their detailed nature remains a mystery. To explore the effects of the initial mass, rotation rate, wind mass loss, and metallicity on the GRB progenitors and the newborn magnetar properties, we evolve 227 of 10-30 M ⊙ single star models from the pre-main sequence to core collapse by using the stellar evolution code MESA. The presupernova properties, the compactness parameter, and the magnetar characteristics of models with different initial parameters are presented. The compactness parameter remains a nonmonotonic function of the initial mass and initial rotation rate when the effects of varying metallicity and the "Dutch" wind scale factor are taken into account. We find that the initial rotation rate and mass play the dominant roles in whether a star can evolve into a GRB progenitor. The minimum rotation rate necessary to generate a magnetar gradually reduces as the initial mass increases. The greater the initial metallicity and "Dutch" wind scale factor, the larger the minimum rotation rate required to produce a magnetar. In other words, massive stars with low metallicity are more likely to harbor magnetars. Furthermore, we present the estimated period, magnetic field strength, and masses of magnetars in all cases. The typical rotational energy of these millisecond magnetars is sufficient to power long-duration GRBs.

Keywords: Magnetars, Massive stars, Gamma-ray bursts, Stellar evolutionary models
Observational Prospects of Double Neutron Star Mergers and Their Multimessenger Afterglows: LIGO Discovery Power, Event Rates, and Diversity. The double neutron star (DNS) merger event GW170817 signifies the first multimessenger (MM) event with electromagnetic-gravitational (EM-GW) observations. LIGO-Virgo-KAGRA observational runs O4-5 promise to detect similar events and as yet unknown GW signals, which require confirmation in two or more detectors with comparable performance. To this end, we quantify duty cycles of comparable science quality of data in coincident H1L1-observations, further to seek consistent event rates of astrophysical transients in upcoming EM-GW surveys. Quite generally, discovery power scales with exposure time, sensitivity, and critically depends on the percentage of time when detectors operate at high quality. We quantify coincident duty cycles over a time-frequency domain W × B, defined by segments of duration W = 8 s, motivated by a long-duration descending GW-chirp during GRB170817A, and the minimum detector noise over about B = 100-250 Hz. This detector yield factor satisfies 1%-25% in S5-6 and O1-O3ab, significantly different from duty cycles of H1 and L1 individually with commensurable impact on consistency in event rates in EM-GW surveys. Significant gain in discovery power for signals whose frequency varies slowly in time may be derived from improving detector yield factors by deploying time-symmetric data analysis methods. For O4-5, these can yield improvements by factors up to ${ \mathcal O }({10}^{5})$ relative to existing data and methods. Furthermore, the diversity of MM afterglows to DNS mergers may be greatest for systems similar to GW170817 but possibly less so for systems of substantially different mass such as GW190425. We summarize our findings with an outlook on EM-GW surveys during O4-5 and perspectives for next-generation GRB missions like THESEUS.

Keywords: Neutron stars, Gravitational wave detectors, Gravitational waves
4FGL J1844.4-0306: High-energy Emission Likely from the Supernova Remnant G29.37 + 0.1. Very-high-energy (VHE) observations have revealed approximately 100 TeV sources in our Galaxy, and a significant fraction of them are under investigation to understand their origin. We report our study of one of them, HESS J1844-030. It is found to be possibly associated with the supernova remnant (SNR) candidate G29.37 + 0.1, and detailed studies of the source region at radio and X-ray frequencies have suggested that this SNR is a composite one, containing a pulsar wind nebula (PWN) powered by a candidate young pulsar. As the GeV source 4FGL J1844.4-0306 is also located in the region with high positional coincidence, we analyze its γ-ray data obtained with the Large Area Telescope on board the Fermi Gamma-ray Space Telescope. We determine the GeV γ-ray emission is extended, described with a log-parabola function. The obtained spectrum can be connected to that of the VHE source HESS J1844-030. Given these properties and those from multifrequency studies, we discuss the origin of the γ-ray emission by considering that the two γ-ray sources are associated. Our modeling indicates that while the TeV part would have either a hadronic (from the SNR) or a leptonic origin (from the putative PWN), the GeV part would arise from a hadronic process. Thus we conclude that 4FGL J1844.4-0306 is likely the GeV counterpart to G29.37 + 0.1.

Keywords: Supernova remnants, Gamma-ray sources, Pulsar wind nebulae
Electron Signal Induced by GRB 221009A on Charged Particle Telescopes of POES and MetOp Satellites. GRB 221009A is a long gamma-ray burst among the most energetic and nearest (z = 0.151) detected so far. The energy fluence of the burst was so large to cause ionization of the upper layers of Earth's atmosphere and also observable signals in satellite-borne particle detectors. Electron signals, with the same GRB time development, can arise from the interaction of energetic photons with the particle detector and support structures. This effect was previously reported for the HEPP-L on board the China Seismo-Electromagnetic Satellite. We searched for the same effect on the particle detectors on board five POES and MetOp satellites. Electron signals in coincidence with the gamma-ray emission of the burst were found in three satellites, which were well illuminated by the GRB. The properties of the found electron signals are reported and discussed.

Keywords: Gamma-ray bursts
Comparing Early Evolution of Flames in X-Ray Bursts in Two and Three Dimensions. We explore the early evolution of flame ignition and spreading on the surface of a neutron star in three dimensions, in the context of X-ray bursts. We look at the nucleosynthesis and morphology of the burning front and compare to two-dimensional axisymmetric simulations to gauge how important a full three-dimensional treatment of the flame is for the early dynamics. Finally, we discuss the progress toward full-star resolved flame simulations.

Keywords: Open source software, Explosive nucleosynthesis, Computational methods, GPU computing, X-ray bursts
The Radio Parallax of the Crab Pulsar: A First VLBI Measurement Calibrated with Giant Pulses. We use four observations with the European very long baseline interferometry (VLBI) network to measure the first precise radio parallax of the Crab Pulsar. We found two in-beam extragalactic sources just outside the Crab Nebula, with one bright enough to use as a background reference source in our data. We use the Crab Pulsar's giant pulses to determine fringe and bandpass calibration solutions, which greatly improved the sensitivity and reliability of our images and allowed us to determine precise positional offsets between the pulsar and the background source. From those offsets, we determine a parallax of π = 0.53 ± 0.06 mas and proper motion of (μ  α , μ  δ ) = (-11.34 ± 0.06, 2.65 ± 0.14) mas yr-1, yielding a distance of $d={1.90}_{-0.18}^{+0.22}\,\mathrm{kpc}$ and transverse velocity of ${v}_{\perp }={104}_{-11}^{+13}\,\mathrm{km}\,{{\rm{s}}}^{-1}$ . These results are consistent with the Gaia 3 measurements, and open up the possibility of far more accurate astrometry with further VLBI observations.

Keywords: Parallax, Very long baseline interferometry, Radio astrometry, Pulsars, Supernova remnants, Radio bursts