adsabs/SciX_UAT_keywords huggingface dataset:
Broken into Pieces: ATLAS and Aliqa Uma as One Single Stream

We present the first spectroscopic measurements of the ATLAS and Aliqa Uma streams from the Southern Stellar Stream Spectroscopic Survey (S5), in combination with the photometric data from the Dark Energy Survey and astrometric data from Gaia. From the coherence of spectroscopic members in radial velocity and proper motion, we find that these two systems are extremely likely to be one stream with discontinuity in morphology and density on the sky (the "kink" feature). We refer to this entire stream as the ATLAS-Aliqa Uma stream, or the AAU stream. We perform a comprehensive exploration of the effect of baryonic substructures and find that only an encounter with the Sagittarius dwarf ∼0.5 Gyr ago can create a feature similar to the observed "kink." In addition, we also identify two gaps in the ATLAS component associated with the broadening in the stream width (the "broadening" feature). These gaps have likely been created by small mass perturbers, such as dark matter halos, as the AAU stream is the most distant cold stream known with severe variations in both the stream surface density and the stream track on the sky. With the stream track, stream distance, and kinematic information, we determine the orbit of the AAU stream and find that it has been affected by the Large Magellanic Cloud, resulting in a misalignment between the proper motion and stream track. Together with the Orphan-Chenab Stream, AAU is the second stream pair that has been found to be a single stream separated into two segments by external perturbation.

Keywords: tidal disruption; stellar kinematics; stellar motion; stellar associations; metallicity; stellar abundances; dark matter; milky way dark matter halo; stellar streams; milky way dynamics
GRB 221009A: Discovery of an Exceptionally Rare Nearby and Energetic Gamma-Ray Burst

We report the discovery of the unusually bright long-duration gamma-ray burst (GRB), GRB 221009A, as observed by the Neil Gehrels Swift Observatory (Swift), Monitor of All-sky X-ray Image, and Neutron Star Interior Composition Explorer Mission. This energetic GRB was located relatively nearby (z = 0.151), allowing for sustained observations of the afterglow. The large X-ray luminosity and low Galactic latitude (b = 4.°3) make GRB 221009A a powerful probe of dust in the Milky Way. Using echo tomography, we map the line-of-sight dust distribution and find evidence for significant column densities at large distances (≳10 kpc). We present analysis of the light curves and spectra at X-ray and UV-optical wavelengths, and find that the X-ray afterglow of GRB 221009A is more than an order of magnitude brighter at T 0 + 4.5 ks than that from any previous GRB observed by Swift. In its rest frame, GRB 221009A is at the high end of the afterglow luminosity distribution, but not uniquely so. In a simulation of randomly generated bursts, only 1 in 104 long GRBs were as energetic as GRB 221009A; such a large E γ,iso implies a narrow jet structure, but the afterglow light curve is inconsistent with simple top-hat jet models. Using the sample of Swift GRBs with redshifts, we estimate that GRBs as energetic and nearby as GRB 221009A occur at a rate of ≲1 per 1000 yr-making this a truly remarkable opportunity unlikely to be repeated in our lifetime.

Keywords: gamma-ray bursts
Global 21 cm Signal Extraction from Foreground and Instrumental Effects. IV. Accounting for Realistic Instrument Uncertainties and Their Overlap with Foreground and Signal Models

All 21 cm signal experiments rely on electronic receivers that affect the data via both multiplicative and additive biases through the receiver's gain and noise temperature. While experiments attempt to remove these biases, the residuals of their imperfect calibration techniques can still confuse signal extraction algorithms. In this paper, the fourth and final installment of our pipeline series, we present a technique for fitting out receiver effects as efficiently as possible. The fact that the gain and global signal, which are multiplied in the observation equation, must both be modeled implies that the model of the data is nonlinear in its parameters, making numerical sampling the only way to explore the parameter distribution rigorously. However, multi-spectra fits, which are necessary to extract the signal confidently as demonstrated in the third paper of the series, often require large numbers of foreground parameters, increasing the dimension of the posterior distribution that must be explored and therefore causing numerical sampling inefficiencies. Building upon techniques in the second paper of the series, we outline a method to explore the full parameter distribution by numerically sampling a small subset of the parameters and analytically marginalizing over the others. We test this method in simulation using a type I Chebyshev bandpass filter gain model and a fast signal model based on a spline between local extrema. The method works efficiently, converging quickly to the posterior signal parameter distribution. The final signal uncertainties are of the same order as the noise in the data.

Keywords: cosmology; astronomy data analysis; reionization
Discovery of 13 New Orbital Periods for Classical Novae

I report new orbital periods (P) for 13 classical novae, based on light curves from TESS, AAVSO, and other public archives. These new nova periods now constitute nearly one-seventh of all known nova periods. Five of my systems have P>1day, which doubles the number of such systems that must have evolved companion stars. (This is simply because ground-based time series have neither the coverage nor the stability required to discover these small-amplitude long periods.) V1016 Sgr has a rare P below the period gap, and suddenly becomes useful for current debates on evolution of novae. Five of the novae (FM Cir, V399 Del, V407 Lup, YZ Ret, and V549 Vel) have the orbital modulations in the tail of the eruption after the transition phase. Soon after the transition, YZ Ret shows a unique set of aperiodic diminishing oscillations, plus YZ Ret shows two highly significant transient periods, 1.1 and 4.5 longer than the orbital period, much like for the superhump phenomenon. I also report an optical 591.27465 s periodicity for V407 Lup, which is coherent and must be tied to the white dwarf spin period.

Keywords: novae
Swift Multiwavelength Follow-up of LVC S200224ca and the Implications for Binary Black Hole Mergers

On 2020 February 24, during their third observing run ("O3"), the Laser Interferometer Gravitational-wave Observatory and Virgo Collaboration detected S200224ca: a candidate gravitational wave (GW) event produced by a binary black hole (BBH) merger. This event was one of the best-localized compact binary coalescences detected in O3 (with 50%/90% error regions of 13/72 deg2), and so the Neil Gehrels Swift Observatory performed rapid near-UV/X-ray follow-up observations. Swift-XRT and UVOT covered approximately 79.2% and 62.4% (respectively) of the GW error region, making S200224ca the BBH event most thoroughly followed-up in near-UV (u-band) and X-ray to date. No likely EM counterparts to the GW event were found by the Swift BAT, XRT, or UVOT, nor by other observatories. Here, we report on the results of our searches for an EM counterpart, both in the BAT data near the time of the merger, and in follow-up UVOT/XRT observations. We also discuss the upper limits we can place on EM radiation from S200224ca, as well as the implications these limits have on the physics of BBH mergers. Namely, we place a shallow upper limit on the dimensionless BH charge, $\hat{q}\lt 1.4\times {10}^{-4}$ , and an upper limit on the isotropic-equivalent energy of a blast wave E < 4.1 × 1051 erg (assuming typical GRB parameters).

Keywords: gravitational waves; high energy astrophysics; black holes; x-ray astronomy; gamma-ray astronomy; gamma-ray bursts; near ultraviolet astronomy
"The Goose" Pulsar Wind Nebula of PSR J1016-5857: The Birth of a Plerion

We report the results of X-ray (Chandra X-ray Observatory (CXO)) and radio (ATCA) observations of the pulsar wind nebula (PWN) powered by the young pulsar PSR J1016-5857, which we dub "the Goose" PWN. In both bands, the images reveal a tail-like PWN morphology that can be attributed to the pulsar's motion. By comparing archival and new CXO observations, we measure the pulsar's proper motion μ = 28.8 ± 7.3 mas yr-1, yielding a projected pulsar velocity v ≈ 440 ± 110 km s-1 (at d = 3.2 kpc); its direction is consistent with the PWN shape. Radio emission from the PWN is polarized, with the magnetic field oriented along the pulsar tail. The radio tail connects to a larger radio structure (not seen in X-rays), which we interpret as a relic PWN (also known as a plerion). The spectral analysis of the CXO data shows that the PWN spectrum softens from Γ = 1.7 to Γ ≈ 2.3-2.5 with increasing distance from the pulsar. The softening can be attributed to the rapid synchrotron burn-off, which would explain the lack of X-ray emission from the older relic PWN. In addition to nonthermal PWN emission, we detected thermal emission from a hot plasma, which we attribute to the host supernova remnant. The radio PWN morphology and the proper motion of the pulsar suggest that the reverse shock passed through the pulsar's vicinity and pushed the PWN to one side.

Keywords: pulsars; neutron stars; rotation powered pulsars; galactic radio sources; extended radiation sources; x-ray sources
Fast Magnetic Wave Could Heat the Solar Low-beta Chromosphere

Magnetohydrodynamic (MHD) waves are candidates for heating the solar chromosphere, although it is still unclear which mode of the wave is dominant in heating. We perform two-dimensional radiative MHD simulation to investigate the propagation of MHD waves in the quiet region of the solar chromosphere. We identify the mode of the shock waves by using the relationship between gas pressure and magnetic pressure across the shock front and calculate their corresponding heating rate through the entropy jump to obtain a quantitative understanding of the wave-heating process in the chromosphere. Our result shows that the fast magnetic wave is significant in heating the low-beta chromosphere. The low-beta fast magnetic waves are generated from high-beta fast acoustic waves via mode conversion crossing the equipartition layer. Efficient mode conversion is achieved by large attacking angles between the propagation direction of the shock waves and the chromospheric magnetic field.

Keywords: solar chromosphere; solar chromospheric heating
On the Plasma Quasi-thermal Noise in the Outer Heliosphere

The recent paper by Li et al. on electron quasi-thermal noise (QTN) in the outer heliosphere is flawed. It assumes the plasma drift speed to be much smaller than the electron thermal speed, even though both quantities are of the same order of magnitude in the outer heliosphere inward of the termination shock, because of the low plasma temperature. In this case, the Langmuir wave dispersion equation and the QTN in the antenna frame are completely changed. Furthermore, these calculations neglect the shot noise, which should produce a large contribution below the plasma frequency with the Voyager antennas in the outer heliosphere.

Keywords: heliosphere; space plasmas; plasma physics; solar wind; space vehicle instruments
Reconstructing Intrinsic Stellar Noise with Stellar Atmospheric Parameters and Chromospheric Activity

Accurately characterizing the intrinsic stellar photometric noise induced by stellar astrophysics, such as stellar activity, granulation, and oscillations, is of crucial importance for detecting transiting exoplanets. In this study, we investigate the relation between the intrinsic stellar photometric noise, quantified by the Kepler combined differential photometric precision (CDPP) metric, and the level of stellar chromospheric activity, indicated by the S-index of Ca II H K lines derived from LAMOST spectra. Our results reveal a clear positive correlation between the S-index and robust rms values of CDPP, with the correlation becoming more significant at higher activity levels and on longer timescales. We have therefore built an empirical relation between the robust rms values of CDPP and the S-index as well as T eff, g, [Fe/H], and the apparent magnitude, with the XGBoost regression algorithm, using the LAMOST–Kepler common star sample as the training set. This method achieves a precision of ∼20 ppm for inferring the intrinsic noise from the S-index and other stellar labels on a 6 hr integration duration. We have applied this empirical relation to the full LAMOST DR7 spectra database and obtained the intrinsic noise predictions for 1,358,275 stars. The resultant catalog is publicly available and expected to be valuable for optimizing target selection for future exoplanet-hunting space missions, such as the Earth 2.0 mission.

Keywords: stellar activity; stellar properties; stellar photometry
Radio Properties of the Quasar J1718+4239, the Proposed Source of the Neutrino Event IceCube-201221A

NVSS J171822+423948 was recently identified as the most probable counterpart of the neutrino event IC-201221A. Based on the highly variable γ-ray, optical, and mid-infrared emission, the dates of the flaring events, and optical spectroscopy in the field of interest, this object was classified as a neutrino-emitting blazar candidate. Since its radio properties were not discussed in detail, we present archival observations. High-amplitude total radio flux density variability supports the connection between the flares at higher energies and the neutrino event.

Keywords: radio loud quasars; cosmological neutrinos; blazars; gamma-ray sources
Observational Evidence for the Origin of High-energy Neutrinos in Parsec-scale Nuclei of Radio-bright Active Galaxies

Observational information on high-energy astrophysical neutrinos is being continuously collected by the IceCube observatory. However, the sources of the neutrinos are still unknown. In this study, we use radio very long baseline interferometry (VLBI) data for a complete VLBI flux density-limited sample of active galactic nuclei (AGNs). We address the problem of the origin of astrophysical neutrinos with energies above 200 TeV in a statistical manner. It is found that AGNs positionally associated with IceCube events have typically stronger parsec-scale cores than the rest of the sample. The posttrial probability of a chance coincidence is 0.2%. We select the four strongest AGNs as highly probable associations: 3C 279, NRAO 530, PKS 1741-038, and OR 103. Moreover, we find an increase of radio emission at frequencies above 10 GHz around neutrino arrival times for several other VLBI-selected AGNs on the basis of RATAN-600 monitoring. The most pronounced example of such behavior is PKS 1502+106. We conclude that AGNs with bright Doppler-boosted jets constitute an important population of neutrino sources. High-energy neutrinos are produced in their central parsec-scale regions, probably in proton-photon interactions at or around the accretion disk. Radio-bright AGNs that are likely associated with neutrinos have very diverse γ-ray properties, suggesting that γ-rays and neutrinos may be produced in different regions of AGNs and not directly related. A small viewing angle of the jet-disk axis is, however, required to detect either of them.

Keywords: neutrino astronomy; active galaxies; galaxy jets; quasars; radio continuum emission
Calibration of the Hα Age-Activity Relation for M Dwarfs

In this work, we calibrate the relationship between Hα emission and M dwarf ages. We compile a sample of 892 M dwarfs with Hα equivalent width (Hα EW) measurements from the literature that are either comoving with a white dwarf of known age (21 stars) or in a known young association (871 stars). In this sample we identify 7 M dwarfs that are new candidate members of known associations. By dividing the stars into active and inactive categories according to their Hα EW and spectral type (SpT), we find that the fraction of active dwarfs decreases with increasing age, and the form of the decline depends on SpT. Using the compiled sample of age calibrators, we find that Hα EW and fractional Hα luminosity (LHα/Lbol) decrease with increasing age. Hα EW for SpT ≤ M7 decreases gradually up until ∼1 Gyr. For older ages, we found only two early M dwarfs that are both inactive and seem to continue the gradual decrease. We also found 14 mid-type M dwarfs, out of which 11 are inactive and present a significant decrease in Hα EW, suggesting that the magnetic activity decreases rapidly after ∼1 Gyr. We fit LHα/Lbol versus age with a broken power law and find an index of $-{0.11}_{-0.01}^{+0.02}$ for ages ≲776 Myr. The index becomes much steeper at older ages, but a lack of field age-calibrators (≫1 Gyr) leaves this part of the relation far less constrained. Finally, from repeated independent measurements for the same stars, we find that 94% of them have a level of Hα EW variability ≤5 Å at young ages (<1 Gyr).

Keywords: low mass stars; astronomy data analysis; catalogs; stellar activity; astrometric binary stars; stellar evolution
Subsurface Thermophysical Properties of Europa's Leading and Trailing Hemispheres as Revealed by ALMA

We present best-fit values of porosity—and the corresponding effective thermal inertiae—determined from three different depths in Europa's near-subsurface (∼1–20 cm). The porosity of the upper ∼20 cm of Europa's subsurface varies between 75% and 50% (Γeff ≈ 50–140 J m‑2 K‑1 s‑1/2) on the leading hemisphere and 50%–40% (Γeff ≈ 140–180 J m‑2 K‑1 s‑1/2) on the trailing hemisphere. Residual maps produced by comparison with these models reveal thermally anomalous features that cannot be reproduced by globally homogeneous porosity models. These regions are compared to Europa's surface terrain and known compositional variations. We find that some instances of warm thermal anomalies are co-located with known geographical or compositional features on both the leading and trailing hemisphere; cool temperature anomalies are well correlated with surfaces previously observed to contain pure, crystalline water ice and the expansive rays of Pwyll crater. Anomalous regions correspond to locations with subsurface properties different from those of our best-fit models, such as potentially elevated thermal inertia, decreased emissivity, or more porous regolith. We also find that ALMA observations at ∼3 mm sound below the thermal skin depth of Europa (∼10–15 cm) for a range of porosity values, and thus do not exhibit features indicative of diurnal variability or residuals similar to other frequency bands. Future observations of Europa at higher angular resolution may reveal additional locations of variable subsurface thermophysical properties, while those at other wavelengths will inform our understanding of the regolith compaction length and the effects of external processes on the shallow subsurface.

Keywords: planetary science; natural satellite surfaces; remote sensing; planetary surfaces; radio astrometry; millimeter astronomy; submillimeter astronomy; ice porosity; thermal properties (ice); europa; galilean satellites
A New Polar Ring Galaxy Discovered in the COSMOS Field

In order to understand the formation and evolution of galaxies fully, it is important to study their three-dimensional gravitational potential for a large sample of galaxies. Since polar-ring galaxies (PRGs) provide useful laboratories for this investigation, we have started our detailed study of a sample of known PRGs by using the data set obtained by the Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP). During the course of this study, we have discovered a new PRG, identified as SDSS J095351.58+012036.1. Its photometric redshift is estimated as z ~ 0.2. The polar ring structure in this PRG appears to be almost perpendicular to the disk of its host galaxy without any disturbed features. Therefore, this PRG will provide us with useful information on the formation of such an undisturbed polar structure. We discuss its photometric properties in detail.

Keywords: galaxy colors; galaxy photometry; galaxy structure
Periodicity Search for Pulsar Binaries with TESS

Pulsar binaries, in particular redback systems, provide good sources to study the pulsar wind flow and its interaction with the companion stars. Fermi-LAT have proposed probable pulsar binary candidates in its catalogs. An orbital modulation search of binary candidates is an effective way to identify pulsar binary sources from the catalog. Transiting Exoplanet Survey Satellite (TESS) observes in survey mode for a large part of the sky and thus provides an excellent data set for the periodicity search of pulsar binary candidates by observing the flux variation, thought to mainly come from the stellar companion. Using TESS data we look for flux modulation of five pulsar binaries (or candidates) with reported orbital periods, including PSR J1023+0038, 3FGL J0523.3-2528, 3FGL J0212.1+5320, 3FGL J0744.1-2523, and PSR J1417-4402, demonstrating that TESS photometric data are very useful in identifying periodicities of redback-like systems. This method can be effective in searches for new pulsar binaries or similar binary systems in the future.

Keywords: astronomy data analysis; binary pulsars; pulsars
SN 2019yvq Does Not Conform to SN Ia Explosion Models

We present new photometric and spectroscopic observations of SN 2019yvq, a Type Ia supernova (SN Ia) exhibiting several peculiar properties including an excess of UV/optical flux within days of explosion, a high Si II velocity, and a low peak luminosity. Photometry near the time of first light places new constraints on the rapid rise of the UV/optical flux excess. A near-infrared spectrum at +173 days after maximum light places strict limits on the presence of H or He emission, effectively excluding the presence of a nearby nondegenerate star at the time of explosion. New optical spectra, acquired at +128 and +150 days after maximum light, confirm the presence of [Ca II] λ7300 and persistent Ca II NIR triplet emission as SN 2019yvq transitions into the nebular phase. The lack of [O I] $\lambda 6300$ emission disfavors the violent merger of two C/O white dwarfs (WDs) but the merger of a C/O WD with a He WD cannot be excluded. We compare our findings with several models in the literature postulated to explain the early flux excess including double-detonation explosions, 56Ni mixing into the outer ejecta during ignition, and interaction with H- and He-deficient circumstellar material. Each model may be able to explain both the early flux excess and the nebular [Ca II] emission, but none of the models can reconcile the high photospheric velocities with the low peak luminosity without introducing new discrepancies.

Keywords: type ia supernovae; white dwarf stars; astrophysical explosive burning; nuclear astrophysics