adsabs/SciX_UAT_keywords huggingface dataset:
Orbital Decay of Double White Dwarfs: Beyond Gravitational-wave Radiation Effects

The traditional description of the orbital evolution of compact-object binaries, like double white dwarfs (DWDs), assumes that the system is driven only by gravitational-wave (GW) radiation. However, the high magnetic fields with intensities of up to gigagausses measured in WDs alert a potential role of the electromagnetic (EM) emission in the evolution of DWDs. We evaluate the orbital dynamics of DWDs under the effects of GW radiation, tidal synchronization, and EM emission by a unipolar inductor generated by the magnetic primary and the relative motion of the nonmagnetic secondary. We show that the EM emission can affect the orbital dynamics for magnetic fields larger than megagausses. We applied the model to two known DWDs, SDSS J0651+2844 and ZTF J1539+5027, for which the GW radiation alone does not fully account for the measured orbital decay rate. We obtain upper limits to the primary's magnetic field strength, over which the EM emission causes an orbital decay faster than observed. The contribution of tidal locking and the EM emission is comparable, and together they can contribute up to 20% to the measured orbital decay rate. We show that the gravitational waveform for a DWD modeled as purely driven by GWs and including tidal interactions and EM emission can have large relative dephasing detectable in the mHz regime of frequencies relevant for space-based detectors like LISA. Therefore, including physics besides GW radiation in the waveform templates is essential to calibrate the GW detectors using known sources, e.g., ZTF J1539+5027, and to infer binary parameters.

Keywords: white dwarf stars; close binary stars; compact binary stars; stellar magnetic fields; gravitational waves
Simultaneous View of FRB 180301 with FAST and NICER during a Bursting Phase

FRB 180301 is one of the most actively repeating fast radio bursts (FRBs) that has shown polarization angle changes in its radio burst emission, an indication for their likely origin in the magnetosphere of a highly magnetized neutron star. We carried out a multiwavelength campaign with the FAST radio telescope and NICER X-ray observatory to investigate any possible X-ray emission temporally coincident with the bright radio bursts. The observations took place on 2021 March 4, 9 and 19. We detected five bright radio bursts with FAST, four of which were strictly simultaneous with the NICER observations. The peak flux density of the radio bursts ranged between 28 and 105 mJy, the burst fluence between 27 and 170 mJy ms, and the burst durations between 1.7 and 12.3 ms. The radio bursts from FRB 180301 exhibited a complex time domain structure, and subpulses were detected in individual bursts, with no significant circular polarization. The linear degree of polarization in the L band reduced significantly compared to the 2019 observations. We do not detect any X-ray emission in excess of the background during the 5, 10, 100 ms, 1 and 100 s time intervals at/around the radio-burst barycenter-corrected arrival times, at a > 5σ confidence level. The 5σ upper limits on the X-ray (a) persistent flux is <7.64 × 10-12 erg cm-2 s-1, equivalent to L X < 2.50 × 1045 erg s-1 and (b) 5 ms fluence is <2 × 10-11 erg cm-2, at the radio burst regions. Using the 5 ms X-ray fluence upper limit, we can estimate the radio efficiency η R/X ≡ L radio/L X-ray ≳ 10-8. The derived lower limit on η R/X is consistent with both magnetospheric models and synchrotron maser models involving relativistic shocks.

Keywords: radio transient sources
Centaurus A: Exploring the Nature of the Hard X-Ray/Soft Gamma-Ray Emission with INTEGRAL

The question of the origin of the hard X-ray/soft gamma-ray emission in Centaurus A (Cen A) persists despite decades of observations. Results from X-ray instruments suggest a jet origin since the implied electron temperature (kT e ) would cause runaway pair production in the corona. In contrast, instruments sensitive to soft gamma rays report electron temperatures indicating that a coronal origin may be possible. In this context, we analyzed archival INTEGRAL/IBIS-ISGRI and SPI data and observations from a 2022 Cen A monitoring program. Our analysis did not find any spectral variability. Thus we combined all observations for long-term average spectra, which were fit with a NuSTAR observation to study the 3.5 keV-2.2 MeV spectrum. Spectral fits using a CompTT model found kT e ~ 550 keV, near runaway pair production. The spectrum was also well described by a log-parabola to model synchrotron self-Compton emission from the jet. Additionally, a spectral fit with the 12 yr catalog Fermi/LAT spectrum using a log-parabola can explain the data up to ~3 GeV. Above ~3 GeV, a power-law excess is present, which has been previously reported in LAT/H.E.S.S. analysis. However, including a coronal spectral component can also describe the data well. In this scenario, the hard X-rays/soft gamma rays are due the corona and the MeV to GeV emission is due to the jet.

Keywords: active galactic nuclei; gamma-rays
Possibilities and Limitations of Kinematically Identifying Stars from Accreted Ultra-faint Dwarf Galaxies

The Milky Way has accreted many ultra-faint dwarf galaxies (UFDs), and stars from these galaxies can be found throughout our Galaxy today. Studying these stars provides insight into galaxy formation and early chemical enrichment, but identifying them is difficult. Clustering stellar dynamics in 4D phase space (E, L z , J r , J z ) is one method of identifying accreted structure that is currently being utilized in the search for accreted UFDs. We produce 32 simulated stellar halos using particle tagging with the Caterpillar simulation suite and thoroughly test the abilities of different clustering algorithms to recover tidally disrupted UFD remnants. We perform over 10,000 clustering runs, testing seven clustering algorithms, roughly twenty hyperparameter choices per algorithm, and six different types of data sets each with up to 32 simulated samples. Of the seven algorithms, HDBSCAN most consistently balances UFD recovery rates and cluster realness rates. We find that, even in highly idealized cases, the vast majority of clusters found by clustering algorithms do not correspond to real accreted UFD remnants and we can generally only recover 6% of UFDs remnants at best. These results focus exclusively on groups of stars from UFDs, which have weak dynamic signatures compared to the background of other stars. The recoverable UFD remnants are those that accreted recently, z accretion ≲ 0.5. Based on these results, we make recommendations to help guide the search for dynamically linked clusters of UFD stars in observational data. We find that real clusters generally have higher median energy and J r , providing a way to help identify real versus fake clusters. We also recommend incorporating chemical tagging as a way to improve clustering results.

Keywords: dwarf galaxies; stellar kinematics; stellar dynamics; galaxy accretion; clustering
Is GW190425 Consistent with Being a Neutron Star-Black Hole Merger?

GW190425 is the second neutron star merger event detected by the Advanced LIGO/Virgo detectors. If interpreted as a double neutron star merger, the total gravitational mass is substantially larger than that of the binary systems identified in the Galaxy. In this work we analyze the gravitational-wave data within the neutron star-black hole merger scenario. For the black hole, we yield a mass of 2.40M-0.32+0.36 M_{⊙} and an aligned spin of 0.141-0.064+0.067. As for the neutron star we find a mass of 1.15-0.13+0.15 M_{⊙} and the dimensionless tidal deformability of 1.4-1.2+3.8 × 103. These parameter ranges are for 90% credibility. The inferred masses of the neutron star and the black hole are not in tension with current observations and we suggest that GW190425 is a viable candidate of a neutron star-black hole merger event. Benefitting from the continual enhancement of the sensitivities of the advanced gravitational detectors and the increase of the number of the observatories, similar events are anticipated to be much more precisely measured in the future and the presence of black holes below the so-called mass gap will be unambiguously clarified. If confirmed, the mergers of neutron stars with (quickly rotating) low-mass black holes are likely important production sites of the heaviest r-process elements.

Keywords: gravitational waves
A Secular Solar System Resonance that Disrupts the Dominant Cycle in Earth's Orbital Eccentricity (g 2 ‑ g 5): Implications for Astrochronology

The planets' gravitational interaction causes rhythmic changes in Earth's orbital parameters (also called Milanković cycles), which have powerful applications in geology and astrochronology. For instance, the primary astronomical eccentricity cycle due to the secular frequency term (g 2‑g 5) (∼405 kyr in the recent past) utilized in deep-time analyses is dominated by the orbits of Venus and Jupiter, i.e., long eccentricity cycle. The widely accepted and long-held view is that (g 2‑g 5) was practically stable in the past and may hence be used as a "metronome" to reconstruct accurate geologic ages and chronologies. However, using state-of-the-art integrations of the solar system, we show here that (g 2‑g 5) can become unstable over long timescales, without major changes in, or destabilization of, planetary orbits. The (g 2‑g 5) disruption is due to the secular resonance σ 12 = (g 1 ‑ g 2) + (s 1 ‑ s 2), a major contributor to solar system chaos. We demonstrate that entering/exiting the σ 12 resonance is a common phenomenon on long timescales, occurring in ∼40% of our solutions. During σ 12-resonance episodes, (g 2‑g 5) is very weak or absent and Earth's orbital eccentricity and climate-forcing spectrum are unrecognizable compared to the recent past. Our results have fundamental implications for geology and astrochronology, as well as climate forcing, because the paradigm that the long eccentricity cycle is stable, dominates Earth's orbital eccentricity spectrum, and has a period of ∼405 kyr requires revision.

Keywords: solar system; orbits; dynamical evolution; planetary climates; orbital resonances
A NICER View on the 2020 Magnetar-like Outburst of PSR J1846-0258

We report on our monitoring of the strong-field magnetar-like pulsar PSR J1846-0258 with the Neutron Star Interior Composition Explorer (NICER) and the timing and spectral evolution during its outburst in 2020 August. Phase-coherent timing solutions were maintained from 2017 March through 2021 November, including a coherent solution throughout the outburst. We detected a large spin-up glitch of magnitude Δν/ν = 3 × 10-6 at the start of the outburst and observed an increase in pulsed flux that reached a factor of more than 10 times the quiescent level, a behavior similar to that of the 2006 outburst. Our monitoring observations in 2020 June and July indicate that the flux was rising prior to the Swift announcement of the outburst on 2020 August 1. We also observed several sharp rises in the pulsed flux following the outburst and the flux reached quiescent level by 2020 November. The pulse profile was observed to change shape during the outburst, returning to the preoutburst shape by 2021. Spectral analysis of the pulsed emission of NICER data shows that the flux increases result entirely from a new blackbody component that gradually fades away while the power law remains nearly constant at its quiescent level throughout the outburst. Joint spectral analysis of NICER and simultaneous NuSTAR data confirms this picture. We discuss the interpretation of the magnetar-like outburst and origin of the transient thermal component in the context of both a pulsar-like and a magnetar-like model.

Keywords: neutron stars
A Comparative Analysis of Machine-learning Models for Solar Flare Forecasting: Identifying High-performing Active Region Flare Indicators

Solar flares create adverse space weather impacting space- and Earth-based technologies. However, the difficulty of forecasting flares, and by extension severe space weather, is accentuated by the lack of any unique flare trigger or a single physical pathway. Studies indicate that multiple physical properties contribute to active region flare potential, compounding the challenge. Recent developments in machine learning (ML) have enabled analysis of higher-dimensional data leading to increasingly better flare forecasting techniques. However, consensus on high-performing flare predictors remains elusive. In the most comprehensive study to date, we conduct a comparative analysis of four popular ML techniques (k nearest neighbors, logistic regression, random forest classifier, and support vector machine) by training these on magnetic parameters obtained from the Helioseismic and Magnetic Imager on board the Solar Dynamics Observatory for the entirety of solar cycle 24. We demonstrate that the logistic regression and support vector machine algorithms perform extremely well in forecasting active region flaring potential. The logistic regression algorithm returns the highest true skill score of 0.967 ± 0.018, possibly the highest classification performance achieved with any strictly parametric study. From a comparative assessment, we establish that magnetic properties like total current helicity, total vertical current density, total unsigned flux, R_VALUE, and total absolute twist are the top-performing flare indicators. We also introduce and analyze two new performance metrics, namely, severe and clear space weather indicators. Our analysis constrains the most successful ML algorithms and identifies physical parameters that contribute most to active region flare productivity.

Keywords: wavelet analysis; solar active region magnetic fields; solar active regions; solar activity; space weather
Temperature and Distance Dependence of Tidal Circularization in Close Binaries: A Catalog of Eclipsing Binaries in the Southern Hemisphere Observed by the TESS Satellite

Tidal forces are important for understanding how close binary stars and compact exoplanetary systems form and evolve. However, tides are difficult to model, and significant uncertainties exist about the strength of tides. Here, we investigate tidal circularization in close binaries using a large sample of well-characterized eclipsing systems. We searched TESS photometry from the southern hemisphere for eclipsing binaries. We derive best-fit orbital and stellar parameters by jointly modeling light curves and spectral energy distributions. To determine the eccentricity distribution of eclipsing binaries over a wide range of stellar temperatures (3000-50,000 K) and orbital separations a/R1 (2-300), we combine our newly obtained TESS sample with eclipsing binaries observed from the ground and by the Kepler mission. We find a clear dependency of stellar temperature and orbital separation in the eccentricities of close binaries. We compare our observations with predictions of the equilibrium and dynamical tides. We find that while cool binaries agree with the predictions of the equilibrium tide, a large fraction of binaries with temperatures between 6250 K and 10,000 K and orbital separations between a/R1 ∼ 4 and 10 are found on circular orbits, contrary to the predictions of the dynamical tide. This suggests that some binaries with radiative envelopes may be tidally circularized significantly more efficiently than usually assumed. Our findings on orbital circularization have important implications also in the context of hot Jupiters, where tides have been invoked to explain the observed difference in the spin-orbit alignment between hot and cool host stars.

Keywords: binary stars; close binary stars; detached binary stars; eclipsing binary stars; light curves; tides; tidal interaction
Post-starburst Galaxies in the Centers of Intermediate-redshift Clusters

We present results from MUSE spatially resolved spectroscopy of 21 post-starburst galaxies in the centers of eight clusters from z ~ 0.3 to z ~ 0.4. We measure spatially resolved star formation histories (SFHs), the time since quenching (t Q ), and the fraction of stellar mass assembled in the past 1.5 Gyr (μ 1.5). The SFHs display a clear enhancement of star formation prior to quenching for 16 out of 21 objects, with at least 10% (and up to >50%) of the stellar mass being assembled in the past 1.5 Gyr and t Q ranging from less than 100 to ~800 Myr. By mapping t Q and μ 1.5, we analyze the quenching patterns of the galaxies. Most galaxies in our sample have quenched their star formation from the outside in or show a side-to-side/irregular pattern, both consistent with quenching by ram pressure stripping. Only three objects show an inside-out quenching pattern, all of which are at the high-mass end of our sample. At least two of them currently host an active galactic nucleus. In two post-starbursts, we identify tails of ionized gas indicating that these objects had their gas stripped by ram pressure very recently. Post-starburst features are also found in the stripped regions of galaxies undergoing ram pressure stripping in the same clusters, confirming the link between these classes of objects. Our results point to ram pressure stripping as the main driver of fast quenching in these environments, with active galactic nuclei playing a role at high stellar masses.

Keywords: galaxy environments; galaxy evolution; galaxy clusters; post-starburst galaxies; e+a galaxies
Early Growth of the Star Formation Rate Function in the Epoch of Reionization: An Approach with Rest-frame Optical Emissions

We present a star formation rate function (SFRF) at z ~ 6 based on star formation rates (SFRs) derived by spectral energy distribution fitting on data from rest-frame UV to optical wavelengths of galaxies in the CANDELS GOODS-South and North fields. The resulting SFRF shows an excess compared to the previous estimations by using rest-frame UV luminosity functions (LFs) corrected for the dust attenuation and is comparable to that estimated from a far-infrared LF. This suggests that the number density of dust-obscured intensively star-forming galaxies at z ~ 6 has been underestimated in the previous approach based only on rest-frame UV observations. We parameterize the SFRF using the Schechter function and obtain the best-fit parameter of the characteristic SFR (SFR*) when the faint-end slope and characteristic number density are fixed. The best-fit SFR* at z ~ 6 is comparable to that at z ~ 2, when the cosmic star formation activity reaches its peak. Together with SFRF estimations with a similar approach using rest-frame UV to optical data, the SFR* is roughly constant from z ~ 2 to ~6 and may decrease above z ~ 6. Since the SFR* is sensitive to the high-SFR end of the SFRF, this evolution of SFR* suggests that the high-SFR end of the SFRF grows rapidly during the epoch of reionization and reaches a similar level observed at z ~ 2.

Keywords: galaxy evolution; galaxy formation; high-redshift galaxies
The Sejong Open Cluster Survey (SOS). VII. A Photometric Study of the Young Open Cluster IC 1590

Young open clusters are ideal laboratories to understand the star formation process. We present deep UBVI and Hα photometry for the young open cluster IC 1590 in the center of the H II region NGC 281. Early-type members are selected from UBV photometric diagrams, and low-mass pre-main-sequence (PMS) members are identified by using Hα photometry. In addition, the published X-ray source list and Gaia astrometric data are also used to isolate probable members. A total of 408 stars are selected as members. The mean reddening obtained from early-type members is ⟨E(B - V)⟩ = 0.40 ± 0.06 (s.d.). We confirm the abnormal extinction law for the intracluster medium. The distance modulus to the cluster determined from the zero-age main-sequence fitting method is 12.3 ± 0.2 mag (d = 2.88 ± 0.28 kpc), which is consistent with the distance $d={2.70}_{-0.20}^{+0.24}$ kpc from the recent Gaia parallaxes. We also estimate the ages and masses of individual members by means of stellar evolutionary models. The mode of the age of PMS stars is about 0.8 Myr. The initial mass function of IC 1590 is derived. It appears to be a steeper shape (Γ = -1.49 ± 0.14) than that of the Salpeter/Kroupa initial mass function for the high-mass regime (m > 1 M⊙). The signature of mass segregation is detected from the difference in the slopes of the initial mass functions for the inner ( $r\lt 2\buildrel{\,\prime}\over{.} 5$ ) and outer regions of this cluster. We finally discuss the star formation history in NGC 281.

Keywords: open star clusters; star formation; pre-main sequence stars; initial mass function
Fermi-LAT Detection of a New Starburst Galaxy Candidate: IRAS 13052-5711

A likely starburst galaxy (SBG), IRAS 13052-5711, which is the most distant SBG candidates discovered to date, was found by analyzing 14.4 yr of data from the Fermi large-area telescope. This SBG's significance level is approximately 6.55σ in the 0.1-500 GeV band. Its spatial position is close to that of 4FGL J1308.9-5730, determined from the Fermi large telescope fourth-source Catalog (4FGL). Its power-law spectral index is approximately 2.1, and its light curve for 14.4 yr has no significant variability. These characteristics are highly similar to those of SBGs found in the past. We calculate the SBG's star formation rate (SFR) to be 29.38 M ⊙ yr-1, which is within the SFR range of SBGs found to date. Therefore, IRAS 13052-5711 is considered to be a likely SBG. In addition, its 0.1-500 GeV luminosity is (3.28 ± 0.67) × 1042 erg s-1, which deviates from the empirical relationship of the γ-ray luminosity and the total infrared luminosity. We considered a hadronic model to explain the GeV spectrum of IRAS 13052-5711.

Keywords: starburst galaxies; gamma-ray astronomy
EIGER IV. The Cool 104 K Circumgalactic Environment of High-redshift Galaxies Reveals Remarkably Efficient Intergalactic Medium Enrichment

We report new observations of the cool diffuse gas around 29, 2.3 < z < 6.3 galaxies using deep JWST/NIRCam slitless grism spectroscopy around the sight line to the quasar J0100+2802. The galaxies span a stellar mass range of $7.1\leqslant {\rm{log}}{M}_{\ast }/{M}_{\odot }\leqslant 10.7$ , and star formation rates (SFRs) of $-0.1\lt \mathrm{log}$ SFR/M ⊙ yr‑1 < 2.3. We find galaxies for seven Mg II absorption systems within 300 kpc of the quasar sight line. The Mg II radial absorption profile falls off sharply with radius, with most of the absorption extending out to 2–3 R 200 of the host galaxies. Six out of seven Mg II absorption systems are detected around galaxies with ${\rm{log}}{M}_{\ast }/{M}_{\odot }\gt $ 9. The Mg II absorption kinematics are shifted from the systemic redshifts of host galaxies with a median absolute velocity ≈ 135 km s‑1 and standard deviation ≈ 85 km s‑1. The high kinematic offset and large radial separation (R > 1.3 R 200), suggest that five out of the seven Mg II absorption systems are not gravitationally bound to their host galaxy. In contrast, most of the cool circumgalactic medium at z < 1 is gravitationally bound. The high incidence of unbound Mg II gas in this work suggests that toward the end of reionization, galaxy halos are in a state of remarkable disequilibrium, and are highly efficient in enriching the intergalactic medium. The two strongest Mg II absorption systems are detected at z ∼ 4.22 and 4.5, the former associated with a merging galaxy system and the latter associated with three kinematically close galaxies. Both of these galaxies reside in local galaxy overdensities, indicating the presence of cool Mg II absorption in two "protogroups" at z > 4.

Keywords: galaxy evolution; high-redshift galaxies; circumgalactic medium; intergalactic medium; emission line galaxies; quasar absorption line spectroscopy