Sazuna/UAT_keywords huggingface dataset:
Variability in Short Gamma-Ray Bursts: Gravitationally Unstable Tidal Tails. Short gamma-ray bursts (GRBs) are thought to result from the merger of two neutron stars (NSs) or an NS and a stellar mass black hole (BH). The final stages of the merger are generally accompanied by the production of one or more tidal "tails" of ejecta, which fall back onto the remnant-disk system at late times. Using the results of a linear stability analysis, we show that if the material comprising these tails is modeled as adiabatic and the effective adiabatic index satisfies γ ≥ 5/3, then the tails are gravitationally unstable and collapse to form small-scale knots. We analytically estimate the properties of these knots, including their spacing along the tidal tail, the total number produced, and their effect on the mass return rate to the merger remnant. We perform hydrodynamical simulations of the disruption of a polytropic (with the polytropic and adiabatic indices γ equal), γ = 2 NS, by a BH and find agreement between the predictions of the linear stability analysis and the distribution of knots that collapse out of the instability. The return of these knots to the BH induces variability in the fallback rate, which can manifest as variability in the light curve of the GRB and—depending on how rapidly the instability operates—the prompt emission. The late-time variability induced by the return of these knots is also consistent with the extended emission observed in some GRBs.

Keywords: Accretion, Hydrodynamical simulations, Gamma-ray bursts, Hydrodynamics, Analytical mathematics
Outburst and Splitting of Interstellar Comet 2I/Borisov. We present Hubble Space Telescope observations of a photometric outburst and splitting event in interstellar comet 2I/Borisov. The outburst, first reported with the comet outbound at ∼2.8 au, was caused by the expulsion of solid particles having a combined cross section ∼100 km2 and a mass in 0.1 mm sized particles ∼2 × 107 kg. The latter corresponds to ∼10-4 of the mass of the nucleus, taken as a sphere of radius 500 m. A transient "double nucleus" was observed on UT 2020 March 30 (about 3 weeks after the outburst), having a cross section ∼0.6 km2 and corresponding dust mass ∼105 kg. The secondary was absent in images taken on and before March 28 and in images taken on and after April 3. The unexpectedly delayed appearance and rapid disappearance of the secondary are consistent with an origin through rotational bursting of one or more large (meter-sized) boulders under the action of outgassing torques, following their ejection from the main nucleus. Overall, our observations reveal that the outburst and splitting of the nucleus are minor events involving a negligible fraction of the total mass: 2I/Borisov will survive its passage through the planetary region largely unscathed.

Keywords: Comet surfaces, Comets, Interstellar objects
The Lowest-frequency Fast Radio Bursts: Sardinia Radio Telescope Detection of the Periodic FRB 180916 at 328 MHz. We report on the lowest-frequency detection to date of three bursts from the fast radio burst FRB 180916.J0158+65, observed at 328 MHz with the Sardinia Radio Telescope (SRT). The SRT observed the periodic repeater FRB 180916.J0158+65 for five days from 2020 February 20 to 24 during a time interval of active radio bursting, and detected the three bursts during the first hour of observations; no more bursts were detected during the remaining ∼30 hr. Simultaneous SRT observations at 1548 MHz did not detect any bursts. Burst fluences are in the range 37 to 13 Jy ms. No relevant scattering is observed for these bursts. We also present the results of the multi-wavelength campaign we performed on FRB 180916.J0158+65, during the five days of the active window. Simultaneously with the SRT observations, others with different time spans were performed with the Northern Cross at 408 MHz, with XMM-Newton, NICER, INTEGRAL, AGILE, and with the TNG and two optical telescopes in Asiago, which are equipped with fast photometers. XMM-Newton obtained data simultaneously with the three bursts detected by the SRT, and determined a luminosity upper limit in the 0.3-10 keV energy range of ∼1045 erg s-1 for the burst emission. AGILE obtained data simultaneously with the first burst and determined a fluence upper limit in the MeV range for millisecond timescales of ${10}^{-8}\,\mathrm{erg}\,{\mathrm{cm}}^{-2}$ . Our results show that absorption from the circumburst medium does not significantly affect the emission from FRB 180916.J0158+65, thus limiting the possible presence of a superluminous supernova around the source, and indicate that a cutoff for the bursting mechanism, if present, must be at lower frequencies. Our multi-wavelength campaign sensitively constrains the broadband emission from FRB 180916.J0158+65, and provides the best limits so far for the electromagnetic response to the radio bursting of this remarkable source of fast radio bursts.

Keywords: Radio transient sources
Detection of Repeating FRB 180916.J0158+65 Down to Frequencies of 300 MHz. We report on the detection of seven bursts from the periodically active, repeating fast radio burst (FRB) source FRB 180916.J0158+65 in the 300-400 MHz frequency range with the Green Bank Telescope (GBT). Emission in multiple bursts is visible down to the bottom of the GBT band, suggesting that the cutoff frequency (if it exists) for FRB emission is lower than 300 MHz. Observations were conducted during predicted periods of activity of the source, and had simultaneous coverage with the Low Frequency Array (LOFAR) and the FRB backend on the Canadian Hydrogen Intensity Mapping Experiment (CHIME) telescope. We find that one of the GBT-detected bursts has potentially associated emission in the CHIME band (400-800 MHz) but we detect no bursts in the LOFAR band (110-190 MHz), placing a limit of $\alpha \gt -1.0$ on the spectral index of broadband emission from the source. We also find that emission from the source is severely band-limited with burst bandwidths as low as ∼40 MHz. In addition, we place the strictest constraint on observable scattering of the source, &lt;1.7 ms at 350 MHz, suggesting that the circumburst environment does not have strong scattering properties. Additionally, knowing that the circumburst environment is optically thin to free-free absorption at 300 MHz, we find evidence against the association of a hyper-compact H II region or a young supernova remnant (age &lt;50 yr) with the source.

Keywords: Radio bursts, Radio transient sources
A Radiatively Quiet Glitch and Anti-glitch in the Magnetar 1E 2259+586. We report on the timing and spectral properties of the soft X-ray emission from the magnetar 1E 2259+586 from 2013 January, ∼8 months after the detection of an anti-glitch, until 2019 September, using the Neil Gehrels Swift and Neutron star Interior Composition ExploreR (NICER) observatories. During this time span, we detect two timing discontinuities. The first, occurring around 5 yr after the 2012 April anti-glitch, is a relatively large spin-up glitch with a fractional amplitude ${\rm{\Delta }}\nu /\nu =1.24(2)\times {10}^{-6}$ . We find no evidence for flux enhancement or change in the spectral or pulse-profile shape around the time of this glitch. This is consistent with the picture that a significant number of magnetar spin-up glitches are radiatively quiet. Approximately 1.5 yr later in 2019 April, 1E 2259+586 exhibited an anti-glitch with spin-down of a fractional amplitude ${\rm{\Delta }}\nu /\nu =-5.8(1)\times {10}^{-7}$ , similar to the fractional change detected in 2012. We do not, however, detect any change to the pulse-profile shape or increase in the rms pulsed flux of the source, nor do we see any possible bursts from its direction around the time of the anti-glitch, all of which occurred during the 2012 event. Hence, similar to spin-up glitches, anti-glitches can occur silently. This may suggest that these phenomena originate in the neutron star interior, and that their locale and triggering mechanism do not necessarily have to be connected to the magnetosphere. Last, our observations suggest that the occurrence rate of spin-up and spin-down glitches is about the same in 1E 2259+586, with the former having a larger net fractional change.

Keywords: Neutron stars, Magnetars, Compact objects
The Accuracy of the Hubble Constant Measurement Verified through Cepheid Amplitudes. The accuracy of the Hubble constant measured with extragalactic Cepheids depends on robust photometry and background estimation in the presence of stellar crowding. The conventional approach accounts for crowding by sampling backgrounds near Cepheids and assuming that they match those at their positions. We show a direct consequence of crowding by unresolved sources at Cepheid sites is a reduction in the fractional amplitudes of their light curves. We use a simple analytical expression to infer crowding directly from the light curve amplitudes of &gt;200 Cepheids in three Type Ia supernovae hosts and NGC 4258 as observed by Hubble Space Telescope—the first near-infrared amplitudes measured beyond the Magellanic Clouds. Where local crowding is minimal, we find near-infrared amplitudes match Milky Way Cepheids at the same periods. At greater stellar densities we find that the empirically measured amplitudes match the values predicted (with no free parameters) from crowding assessed in the conventional way from local regions, confirming their accuracy for estimating the background at the Cepheid locations. Extragalactic Cepheid amplitudes would need to be ∼20% smaller than measured to indicate additional, unrecognized crowding as a primary source of the present discrepancy in H0. Rather, we find the amplitude data constrains a systematic mis-estimate of Cepheid backgrounds to be 0.029 ± 0.037 mag, more than 5× smaller than the size of the present ∼0.2 mag tension in H0. We conclude that systematic errors in Cepheid backgrounds do not provide a plausible resolution to the Hubble tension.

Keywords: Cosmology, CCD photometry, Light curves, Distance indicators, Hubble constant, Cepheid variable stars, Cepheid distance
GW190814: Gravitational Waves from the Coalescence of a 23 Solar Mass Black Hole with a 2.6 Solar Mass Compact Object. We report the observation of a compact binary coalescence involving a 22.2-24.3 M⊙ black hole and a compact object with a mass of 2.50-2.67 M⊙ (all measurements quoted at the 90% credible level). The gravitational-wave signal, GW190814, was observed during LIGO's and Virgo's third observing run on 2019 August 14 at 21:10:39 UTC and has a signal-to-noise ratio of 25 in the three-detector network. The source was localized to 18.5 deg2 at a distance of ${241}_{-45}^{+41}$ Mpc; no electromagnetic counterpart has been confirmed to date. The source has the most unequal mass ratio yet measured with gravitational waves, ${0.112}_{-0.009}^{+0.008}$ , and its secondary component is either the lightest black hole or the heaviest neutron star ever discovered in a double compact-object system. The dimensionless spin of the primary black hole is tightly constrained to ≤0.07. Tests of general relativity reveal no measurable deviations from the theory, and its prediction of higher-multipole emission is confirmed at high confidence. We estimate a merger rate density of 1-23 Gpc-3 yr-1 for the new class of binary coalescence sources that GW190814 represents. Astrophysical models predict that binaries with mass ratios similar to this event can form through several channels, but are unlikely to have formed in globular clusters. However, the combination of mass ratio, component masses, and the inferred merger rate for this event challenges all current models of the formation and mass distribution of compact-object binaries.

Keywords: Gravitational wave detectors, Compact binary stars, Gravitational wave sources, Gravitational wave astronomy, Gravitational waves, Astrophysical black holes
Radio Power from a Direct-collapse Black Hole in CR7. The leading contenders for the seeds of the first quasars are direct-collapse black holes (DCBHs) formed during catastrophic baryon collapse in atomically cooled halos at z ∼ 20. The discovery of the Lyα emitter CR7 at z = 6.6 was initially held to be the first detection of a DCBH, although this interpretation has since been challenged on the grounds of Spitzer IRAC and Very Large Telescope X-Shooter data. Here we determine if radio flux from a DCBH in CR7 could be detected and discriminated from competing sources of radio emission in the halo such as young supernovae and H II regions. We find that a DCBH would emit a flux of 10-200 nJy at 1.0 GHz, far greater than the sub-nJy signal expected for young supernovae but on par with continuum emission from star-forming regions. However, radio emission from a DCBH in CR7 could be distinguished from free-free emission from H II regions by its spectral evolution with frequency and could be detected by the Square Kilometre Array in the coming decade.

Keywords: Supermassive black holes, Intermediate-mass black holes, Early universe, Population III stars, Quasars, Primordial galaxies, Reionization, High-redshift galaxies
Fast Radio Bursts from Reconnection in a Magnetar Magnetosphere. The nearly 100% linear polarization has been reported for a few fast radio bursts (FRBs). This finding places severe limits on the emission mechanism. I argue that the completely polarized radiation could be generated in the course of relativistic magnetic reconnection in the outer magnetosphere of the magnetar. At the onset of the magnetar flare, a large-scale magnetic perturbation forms a magnetic pulse, which propagates from the flare cite outward. The pulse strongly compresses magnetospheric plasma and pushes it away. The high-frequency MHD waves are generated when the magnetic pulse reaches the current sheet separating, just beyond the light cylinder, the oppositely directed magnetic fields. Coalescence of magnetic islands in the reconnecting current sheet produces magnetosonic waves, which propagate away on the top of the magnetic pulse and escape in the far zone of the wind as radio waves polarized along the rotational axis of the magnetar. I estimate parameters of the outgoing radiation and show that they are compatible with the observed properties of FRBs.

Keywords: Magnetohydrodynamics, Non-thermal radiation sources, Plasma astrophysics
Application of an X-Ray Clumpy Torus Model (XCLUMPY) to 10 Obscured Active Galactic Nuclei Observed with Suzaku and NuSTAR. We apply XCLUMPY, an X-ray spectral model from a clumpy torus in an active galactic nucleus (AGN), to the broadband X-ray spectra of 10 obscured AGNs observed with both Suzaku and NuSTAR. The infrared spectra of these AGNs were analyzed by Ichikawa et al. with the CLUMPY code. Because XCLUMPY adopts the same clump distribution as that in the CLUMPY, we can directly compare the torus parameters obtained from the X-ray spectra and those from the infrared spectra. The torus angular widths determined from the infrared spectra (σIR) are systematically larger than those from the X-ray data (σX); the difference ( ${\sigma }_{\mathrm{IR}}-{\sigma }_{{\rm{X}}}$ ) correlates with the inclination angle determined from the X-ray spectrum. These results can be explained by the contribution from dusty polar outflows to the observed infrared flux, which becomes more significant at higher inclinations (more edge-on views). The ratio of the hydrogen column density to the V-band extinction in the line-of-sight absorber shows a large scatter (≃1 dex) around the Galactic value, suggesting that a significant fraction of AGNs have dust-rich circumnuclear environments.

Keywords: Supermassive black holes, High energy astrophysics, Seyfert galaxies, X-ray active galactic nuclei, Active galactic nuclei, Astrophysical black holes
Accretion Flow Evolution of a New Black Hole Candidate MAXI J1348-630 during the 2019 Outburst. Galactic black hole (BH) candidate MAXI J1348-630 was recently discovered by MAXI and Swift/BAT satellites during its first outburst in 2019 January, which continued for ∼4 months. We study the spectral and timing properties of the source in detail. The combined 1-150 keV Swift/XRT, Swift/BAT, and MAXI/GSC spectra are investigated with the two-component advective flow (TCAF) solution. Physical flow parameters of TCAF, such as the Keplerian disk accretion rate, the sub-Keplerian halo accretion rate, the shock location, and the shock compression ratio, are estimated from our spectral fits. Based on the variation of flux in soft and hard X-ray ranges, the hardness ratio, TCAF model fitted accretion rates, and the accretion rate ratio, we show how the source evolved through four spectral states, viz., hard, hard-intermediate, soft-intermediate, and soft, in rising and declining states. Low-frequency quasi-periodic oscillations are observed in two observations during the rising phase of the outburst. From the spectral analysis, we estimate the mass of the BH to be ${9.1}_{-1.2}^{+1.6}$ M⊙. We also find that the viscous timescale in this outburst is ∼3.5 days. The distance of the source is also estimated as 5-10 kpc from state transition luminosity.

Keywords: Accretion, Stellar mass black holes, Astrophysical black holes
Dissecting the Strong-lensing Galaxy Cluster MS 0440.5+0204. I. The Mass Density Profile. We present a parametric strong-lensing modeling of the galaxy cluster MS 0440.5+0204 (located at z = 0.19). We have performed a strong-lensing mass reconstruction of the cluster using three different models. The first model uses the image positions of four multiply imaged systems (providing 26 constraints). The second one combines strong-lensing constraints with dynamical information (velocity dispersion) of the cluster. The third one uses the mass calculated from weak lensing as an additional constraint. Our three models reproduce equally well the image positions of the arcs, with an rms image equal to ≍0"5. However, in the third model, the inclusion of the velocity dispersion and the weak-lensing mass allows us to obtain better constraints in the scale radius and the line-of-sight velocity dispersion of the mass profile. For this model, we obtain rs = ${132}_{-32}^{+30}$ kpc, ${\sigma }_{s}={1203}_{-47}^{+46}$ km s-1, M200 = ${3.1}_{-0.6}^{+0.6}$ ×1014 ${M}_{\odot }$ , and a high concentration c200 = ${9.9}_{-1.4}^{+2.2}$ . Finally, we used our derived mass profile to calculate the mass up to 1.5 Mpc. We compare it with X-ray estimates previously reported, finding a good agreement.

Keywords: Galaxy clusters, Gravitational lensing, Dark matter
Measuring HERA's Primary Beam in Situ: Methodology and First Results. The central challenge in 21 cm cosmology is isolating the cosmological signal from bright foregrounds. Many separation techniques rely on the accurate knowledge of the sky and the instrumental response, including the antenna primary beam. For drift-scan telescopes, such as the Hydrogen Epoch of Reionization Array (HERA), that do not move, primary beam characterization is particularly challenging because standard beam-calibration routines do not apply (Cornwell et al.) and current techniques require accurate source catalogs at the telescope resolution. We present an extension of the method from Pober et al. where they use beam symmetries to create a network of overlapping source tracks that break the degeneracy between source flux density and beam response and allow their simultaneous estimation. We fit the beam response of our instrument using early HERA observations and find that our results agree well with electromagnetic simulations down to a -20 dB level in power relative to peak gain for sources with high signal-to-noise ratio. In addition, we construct a source catalog with 90 sources down to a flux density of 1.4 Jy at 151 MHz.

Keywords: Cosmology, Radio astronomy, H I line emission
MMS Observations of Accelerated Interstellar Pickup He<SUP>+</SUP> Ions at an Interplanetary Shock. Interstellar pickup ions (PUI) are interstellar neutrals that have been ionized in transit through the heliosphere via charge exchange or photoionization. These new PUIs then "freeze" into the solar wind (SW) and move with the bulk SW velocity (VSW). They also begin to gyrate around the local magnetic field with VSW, resulting in a maximum PUI velocity of 2 ∗ VSW. Understanding how He+ PUIs are accelerated at shocks in space provides valuable insights into shock dynamics and shock acceleration mechanisms. On 2018 January 8, while the Magnetospheric Multiscale (MMS) Mission was in the SW, it observed the forward shock of a corotating interaction region. In this work, we analyze the upstream and downstream velocity distributions of He+ for this quasiperpendicular, marginally supercritical (θBn = 67°, MA = 2.8) interplanetary shock. We derive average two-dimensional pitch-angle distributions in the field-aligned SW frame, as well as reduced one-dimensional velocity distributions for selected upstream and downstream intervals. We find that the shock accelerates He+ largely perpendicular to the magnetic field, consistent with shock reflection. Furthermore, we derive a measured ratio of accelerated He+ ions by estimating a maximum speed in the downstream frame, above which we assume that He+ ions have been accelerated by their interaction with the shock. The measured acceleration ratio, RMeasured = 0.14, is then compared to a theoretical ratio derived from a simple model of the upstream distribution, RTheoretical = 0.06.

Keywords: Interplanetary particle acceleration, Interplanetary shocks
Tidal Inflation Reconciles Low-density Sub-Saturns with Core Accretion. While the solar system contains no planets between the sizes of Uranus and Saturn, our current exoplanet census includes several dozen such planets with well-measured masses and radii. These sub-Saturns exhibit a diversity of bulk densities, ranging from ∼0.1 to 3 g cm-3. When modeled simply as hydrogen/helium envelopes atop rocky cores, this diversity in densities translates to a diversity in planetary envelope fractions, fenv = Menv/Mp, ranging from ∼10% to ∼50%. Planets with fenv ≈ 50% pose a challenge to traditional models of giant planet formation by core-nucleated accretion, which predict the onset of runaway gas accretion when Menv ∼ Mcore. Here, we show that many of these apparent fenv ≈ 50% planets are less envelope-rich than they seem, after accounting for tidal heating. We present a new framework for modeling sub-Saturn interiors that incorporates envelope inflation due to tides, which are driven by the observed nonzero eccentricities, as well as potential obliquities. Consequently, when we apply our models to known sub-Saturns, we infer lower fenv than tides-free estimates. We present a case study of K2-19 b, a moderately eccentric sub-Saturn. Neglecting tides, K2-19 b appears to have fenv ≈ 50%, poised precariously near the runaway threshold; by including tides, however, we find fenv ≈ 10%, resolving the tension. Through a systematic analysis of 4-8 R⊕ planets, we find that most (but not all) of the similarly envelope-rich planets have more modest envelopes of fenv ≈ 10%-20%. Thus, many sub-Saturns may be understood as sub-Neptunes that have undergone significant radius inflation, rather than a separate class of objects. Tidally induced radius inflation likely plays an important role in other size classes of planets including ultra-low-density Jupiter-size planets like WASP-107 b.

Keywords: Exoplanets, Exoplanet tides, Exoplanet structure, Extrasolar gaseous giant planets, Exoplanet atmospheres