bluuebunny/crossref_metadata_2025_split huggingface dataset:
Numerical Modeling of Spectral Hardening at a Finite-width Shock
Authors: Xu Y. D. , Li G. , Yao S. 
Published: June 2022

Abstract
Spectral hardening has been identified in solar flare hard X-ray observations for several decades and remains a puzzle. We examine spectral hardening under the diffusive shock acceleration mechanism using numerical simulations. The hardening is related to the finite width of the shock and is controlled by the shock Péclet number. We implement two different types of Monte Carlo simulations. The first is based on the backward stochastic differential equation method, where the Parker transport equation is solved by casting it to a set of stochastic different equations, and by following the trajectories of individual quasiparticles. In the second approach, we follow real particles and particles are assumed to move freely between scatterings from magnetic turbulence in the plasma. The scattering is modeled as either large-angle hard-sphere elastic collision, or small-angle pitch-angle scattering. We show that the results from these two approaches agree well with each other and agree with analytical results. We also use a Pan-spectrum form to fit the resulting spectra.
The Mechanism of Efficient Electron Acceleration at Parallel Nonrelativistic Shocks
Authors: Shalaby Mohamad , Lemmerz Rouven , Thomas Timon , Pfrommer Christoph 
Published: June 2022

Abstract
Thermal electrons cannot directly participate in the process of diffusive acceleration at electron–ion shocks because their Larmor radii are smaller than the shock transition width: this is the well-known electron injection problem of diffusive shock acceleration. Instead, an efficient pre-acceleration process must exist that scatters electrons off of electromagnetic fluctuations on scales much shorter than the ion gyroradius. The recently found intermediate-scale instability provides a natural way to produce such fluctuations in parallel shocks. The instability drives comoving (with the upstream plasma) ion–cyclotron waves at the shock front and only operates when the drift speed is smaller than half of the electron Alfvén speed. Here we perform particle-in-cell simulations with the SHARP code to study the impact of this instability on electron acceleration at parallel nonrelativistic, electron–ion shocks. To this end, we compare a shock simulation in which the intermediate-scale instability is expected to grow to simulations where it is suppressed. In particular, the simulation with an Alfvénic Mach number large enough to quench the intermediate instability shows a great reduction (by two orders of magnitude) of the electron acceleration efficiency. Moreover, the simulation with a reduced ion-to-electron mass ratio (where the intermediate instability is also suppressed) not only artificially precludes electron acceleration but also results in erroneous electron and ion heating in the downstream and shock transition regions. This finding opens up a promising route for a plasma physical understanding of diffusive shock acceleration of electrons, which necessarily requires realistic mass ratios in simulations of collisionless electron–ion shocks.
ALMA Lensing Cluster Survey: ALMA-Herschel Joint Study of Lensed Dusty Star-forming Galaxies across z ≃ 0.5 – 6
Authors: Sun Fengwu , Egami Eiichi , Fujimoto Seiji , Rawle Timothy , Bauer Franz E. , Kohno Kotaro , Smail Ian , Pérez-González Pablo G. , Ao Yiping , Chapman Scott C. , Combes Francoise , Dessauges-Zavadsky Miroslava , Espada Daniel , González-López Jorge , Koekemoer Anton M. , Kokorev Vasily , Lee Minju M. , Morokuma-Matsui Kana , Muñoz Arancibia Alejandra M. , Oguri Masamune , Pelló Roser , Ueda Yoshihiro , Uematsu Ryosuke , Valentino Francesco , Van der Werf Paul , Walth Gregory L. , Zemcov Michael , Zitrin Adi 
Published: June 2022

Abstract
We present an ALMA-Herschel joint analysis of sources detected by the ALMA Lensing Cluster Survey (ALCS) at 1.15 mm. Herschel/PACS and SPIRE data at 100–500 μm are deblended for 180 ALMA sources in 33 lensing cluster fields that are detected either securely (141 sources; in our main sample) or tentatively at S/N ≥ 4 with cross-matched HST/Spitzer counterparts, down to a delensed 1.15 mm flux density of ∼0.02 mJy. We performed far-infrared spectral energy distribution modeling and derived the physical properties of dusty star formation for 125 sources (109 independently) that are detected at >2σ in at least one Herschel band. A total of 27 secure ALCS sources are not detected in any Herschel bands, including 17 optical/near-IR-dark sources that likely reside at z = 4.2 ± 1.2. The 16th, 50th, and 84th percentiles of the redshift distribution are 1.15, 2.08, and 3.59, respectively, for ALCS sources in the main sample, suggesting an increasing fraction of z ≃ 1 − 2 galaxies among fainter millimeter sources (f
1150 ∼ 0.1 mJy). With a median lensing magnification factor of

μ
=

2.6

−
0.8

+
2.6

, ALCS sources in the main sample exhibit a median intrinsic star formation rate of

94

−
54

+
84

M
⊙ yr−1, lower than that of conventional submillimeter galaxies at similar redshifts by a factor of ∼3. Our study suggests weak or no redshift evolution of dust temperature with L
IR < 1012
L
⊙ galaxies within our sample at z ≃ 0 − 2. At L
IR > 1012
L
⊙, the dust temperatures show no evolution across z ≃ 1–4 while being lower than those in the local universe. For the highest-redshift source in our sample (z = 6.07), we can rule out an extreme dust temperature (>80 K) that was reported for MACS0416 Y1 at z = 8.31.
Generalized Fluid Models of the Braginskii Type
Authors: Hunana P. , Passot T. , Khomenko E. , Martínez-Gómez D. , Collados M. , Tenerani A. , Zank G. P. , Maneva Y. , Goldstein M. L. , Webb G. M. 
Published: June 2022

Abstract
Several generalizations of the well-known fluid model of Braginskii (1965) are considered. We use the Landau collisional operator and the moment method of Grad. We focus on the 21-moment model that is analogous to the Braginskii model, and we also consider a 22-moment model. Both models are formulated for general multispecies plasmas with arbitrary masses and temperatures, where all of the fluid moments are described by their evolution equations. The 21-moment model contains two “heat flux vectors” (third- and fifth-order moments) and two “viscosity tensors” (second- and fourth-order moments). The Braginskii model is then obtained as a particular case of a one ion–electron plasma with similar temperatures, with decoupled heat fluxes and viscosity tensors expressed in a quasistatic approximation. We provide all of the numerical values of the Braginskii model in a fully analytic form (together with the fourth- and fifth-order moments). For multispecies plasmas, the model makes the calculation of the transport coefficients straightforward. Formulation in fluid moments (instead of Hermite moments) is also suitable for implementation into existing numerical codes. It is emphasized that it is the quasistatic approximation that makes some Braginskii coefficients divergent in a weakly collisional regime. Importantly, we show that the heat fluxes and viscosity tensors are coupled even in the linear approximation, and that the fully contracted (scalar) perturbations of the fourth-order moment, which are accounted for in the 22-moment model, modify the energy exchange rates. We also provide several appendices, which can be useful as a guide for deriving the Braginskii model with the moment method of Grad.
New Fe i Level Energies and Line Identifications from Stellar Spectra. III. Initial Results from UV, Optical, and Infrared Spectra
Authors: Peterson Ruth C. , Kurucz Robert L. 
Published: June 2022

Abstract
The spectrum of neutral iron is critical to astrophysics, yet furnace laboratory experiments cannot reach high-lying Fe i levels. Instead, Peterson & Kurucz and Peterson et al. adopted ultraviolet (UV) and optical spectra of warm stars to identify and assign energies for 124 Fe i levels with 1900 detectable Fe i lines, and to derive astrophysical gf values for over 1000 of these. An energy value was assumed for each unknown Fe i level, and confirmed if the wavelengths predicted in updated Kurucz Fe i calculations matched the wavelengths of four or more unidentified lines in the observed spectra. Nearly all these identifications were for LS levels, those characterized by spin–orbit coupling, whose lines fall primarily at UV and optical wavelengths. This work contributes nearly 100 new Fe i level identifications. Thirty-nine LS levels are identified largely by incorporating published positions of unidentified laboratory Fe i lines with wavelengths <2000 Å. Adding infrared (IR) spectra provided 60 Fe i jK levels, where a single outer electron orbits a compact core. Their weak IR lines are searchable, because their mutual energies obey tight relationships. For each new Fe i level, this work again makes publicly available its identification, its energy, and a list of its potentially detectable lines with theoretical gf values, totalling >16,000 lines. For over 2000 of these, this work provides astrophysical gf values adjusted semiempirically to fit the stellar spectra. The potential impact of this work on modeling UV and IR stellar spectra is noted.
A Compound Poisson Generator Approach to Point-source Inference in Astrophysics
Authors: Collin Gabriel H. , Rodd Nicholas L. , Erjavec Tyler , Perez Kerstin 
Published: June 2022

Abstract
The identification and description of point sources is one of the oldest problems in astronomy, yet even today the correct statistical treatment for point sources remains one of the field’s hardest problems. For dim or crowded sources, likelihood-based inference methods are required to estimate the uncertainty on the characteristics of the source population. In this work, a new parametric likelihood is constructed for this problem using compound Poisson generator (CPG) functionals that incorporate instrumental effects from first principles. We demonstrate that the CPG approach exhibits a number of advantages over non-Poissonian template fitting (NPTF)—an existing method—in a series of test scenarios in the context of X-ray astronomy. These demonstrations show that the effect of the point-spread function, effective area, and choice of point-source spatial distribution cannot, generally, be factorized as they are in NPTF, while the new CPG construction is validated in these scenarios. Separately, an examination of the diffuse-flux emission limit is used to show that most simple choices of priors on the standard parameterization of the population model can result in unexpected biases: when a model comprising both a point-source population and diffuse component is applied to this limit, nearly all observed flux will be assigned to either the population or to the diffuse component. A new parameterization is presented for these priors that properly estimates the uncertainties in this limit. In this choice of priors, CPG correctly identifies that the fraction of flux assigned to the population model cannot be constrained by the data.
The R-process Alliance: A Nearly Complete R-process Abundance Template Derived from Ultraviolet Spectroscopy of the R-process-enhanced Metal-poor Star HD 222925*
Authors: Roederer Ian U. , Lawler James E. , Den Hartog Elizabeth A. , Placco Vinicius M. , Surman Rebecca , Beers Timothy C. , Ezzeddine Rana , Frebel Anna , Hansen Terese T. , Hattori Kohei , Holmbeck Erika M. , Sakari Charli M. 
Published: June 2022

Abstract
We present a nearly complete rapid neutron-capture process (r-process) chemical inventory of the metal-poor ([Fe/H] = −1.46 ± 0.10) r-process-enhanced ([Eu/Fe] = +1.32 ± 0.08) halo star HD 222925. This abundance set is the most complete for any object beyond the solar system, with a total of 63 metals detected and seven with upper limits. It comprises 42 elements from 31 ≤ Z ≤ 90, including elements rarely detected in r-process-enhanced stars, such as Ga, Ge, As, Se, Cd, In, Sn, Sb, Te, W, Re, Os, Ir, Pt, and Au. We derive these abundances from an analysis of 404 absorption lines in ultraviolet spectra collected using the Space Telescope Imaging Spectrograph on the Hubble Space Telescope and previously analyzed optical spectra. A series of appendices discusses the atomic data and quality of fits for these lines. The r-process elements from Ba to Pb, including all elements at the third r-process peak, exhibit remarkable agreement with the solar r-process residuals, with a standard deviation of the differences of only 0.08 dex (17%). In contrast, deviations among the lighter elements from Ga to Te span nearly 1.4 dex, and they show distinct trends from Ga to Se, Nb through Cd, and In through Te. The r-process contribution to Ga, Ge, and As is small, and Se is the lightest element whose production is dominated by the r-process. The lanthanide fraction, log X
La = −1.39 ± 0.09, is typical for r-process-enhanced stars and higher than that of the kilonova from the GW170817 neutron-star merger event. We advocate adopting this pattern as an alternative to the solar r-process-element residuals when confronting future theoretical models of heavy-element nucleosynthesis with observations.
NuSTAR Observations of 52 Compton-thick Active Galactic Nuclei Selected by the Swift/Burst Alert Telescope All-sky Hard X-Ray Survey
Authors: Tanimoto Atsushi , Ueda Yoshihiro , Odaka Hirokazu , Yamada Satoshi , Ricci Claudio 
Published: June 2022

Abstract
We present systematic broadband X-ray spectral analysis of 52 Compton-thick (

24
≤
log

N

H

LOS

/

cm

−
2

) active galactic nucleus (CTAGN) candidates selected by the Swift/Burst Alert Telescope all-sky hard X-ray survey observed with Chandra, X-ray Multi-Mirror Mission-Newton (XMM-Newton), Swift/X-Ray Telescope, Suzaku, and NuSTAR. The XMM-Newton data of 10 objects and the NuSTAR data of 15 objects are published for the first time. We use an X-ray spectral model from a clumpy torus (XClumpy) to determine the torus properties. As a result, the hydrogen column density along the line of sight

N

H

LOS

obtained from the XClumpy model indicates that 24 objects are Compton-thin AGNs and 28 objects are CTAGNs in a 90% confidence interval. The main reason is the difference in the torus model applied. The hydrogen column density along the equatorial direction

N

H

Equ

of CTAGNs inferred from the XClumpy model is larger than that of less obscured AGNs. The Compton-thin torus covering factor C
22 obtained from the XClumpy model is consistent with that of Ricci et al. in the low Eddington ratio (

log

R

Edd

≤
−
1.0

), whereas C
22 inferred from the XClumpy model is larger than that of Ricci et al. in the high Eddington ratio (

−
1.0
≤
log

R

Edd

). The average value of the Compton-thick torus covering factor C
24 obtained from the XClumpy model is

36

−
4

+
4

%. This value is larger than that of Ricci et al. (

C

24

≃

27

−
4

+
4

%) based on the assumption that all AGNs have intrinsically the same torus structure. These results suggest that the structure of CTAGNs may be intrinsically different from that of less obscured AGNs.
Three-month Monitoring of the Variability toward W51 IRS2 with Ammonia, Water, and Methanol Transitions
Authors: Zhang Yan-Kun , Chen Xi , Sobolev Andrej M. , Shen Zhi-Qiang , Li Bin , Zhao Zhang 
Published: June 2022

Abstract
A four-epoch monitoring program spanning ∼three months (from 2020 January 8 to April 7) for ammonia, water, and methanol transitions toward the high-mass star-forming region W51 IRS2 was conducted using the Shanghai 65 m Tianma Radio Telescope with its K-band (18–26.5 GHz) receiver. In total, 33 ammonia transitions and 16 methanol transitions were detected toward the target at least once during this monitoring program. Among them, 14 ammonia and 4 methanol transitions show maser emission characteristics. Rapid variabilities (including both increases and decreases) in the ammonia and methanol transitions were detected from both maser and thermal emissions during the three months of the monitoring. In addition, H2O masers with obvious variability were also detected. The results of the rotation diagram analysis for the ammonia and methanol quasi-thermal transitions show the variations in their rotational temperatures during the monitoring. The derived temperatures from the transitions with larger upper energies (E

u
/κ) generally decreased over the whole monitoring period, from January 8 to April 7, but those with smaller E

u
/κ first increased from January 8 to April 1, then rapidly decreased from April 1 to April 7. These findings support the suggestion that an inside-out heatwave propagation in W51 IRS2 was involved with the accretion burst over a short duration (only on the order of months) and caused the drastic variability behaviors of the different line transitions during high-mass star formation.
An Insight-HXMT Dedicated 33 day Observation of SGR J1935+2154. I. Burst Catalog
Authors: Cai Ce , Xue Wang-Chen , Li Cheng-Kui , Xiong Shao-Lin , Zhang Shuang-Nan , Lin Lin , Li Xiao-Bo , Ge Ming-Yu , Zhao Hai-Sheng , Song Li-Ming , Lu Fang-Jun , Zhang Shu , Zhang Yan-Qiu , Xiao Shuo , Tuo You-Li , Yi Qi-Bin , Wei Guo Zhi , Lun Xie Sheng , Zhao Yi , Zhang Zhen , Li Qing-Xin , Liu Jia-Cong , Zheng Chao , Wang Ping 
Published: June 2022

Abstract
Magnetars are neutron stars with an extreme magnetic field and sometimes manifest as soft gamma-ray repeaters (SGRs). SGR J1935+2154 is one of the most prolific bursters and the first confirmed source of a fast radio burst (FRB; i.e., FRB 200428). Encouraged by the discovery of the first X-ray counterpart of FRBs, the Insight-Hard X-ray Modulation Telescope (Insight-HXMT) implemented a dedicated 33-day-long Target of Opportunity observation of SGR J1935+2154 since 2020 April 28. With the HE, ME, and LE telescopes, Insight-HXMT provides a thorough monitoring of burst activity evolution of SGR J1935+2154, in a very broad energy range (1–250 keV) with high temporal resolution and high sensitivity, resulting in a unique valuable data set for detailed studies of SGR J1935+2154. In this work, we conduct a comprehensive analysis of this observation, including detailed burst search, identification, and temporal analyses. After carefully removing false triggers, we find a total of 75 bursts from SGR J1935+2154, out of which 70 are single pulsed. The maximum burst rate is about 56 bursts day−1. Both the burst duration and the waiting time between two successive bursts follow lognormal distributions, consistent with previous studies. We also find that bursts with longer duration (some are multipulsed) tend to occur during the period with relatively high burst rate. There is no correlation between the waiting time and the fluence or duration of either the former or latter burst. It also seems that there is no correlation between burst duration and hardness ratio, in contrast to some previous reports. In addition, we do not find any X-ray burst associated with any reported radio bursts except for FRB 200428.
Dust Extinction Law in Nearby Star-resolved Galaxies. II. M33 Traced by Supergiants
Authors: Wang 王 Yuxi 钰溪 , Gao 高 Jian 健 , Ren 任 Yi 逸 , Chen 陈 Bingqiu 丙秋 
Published: June 2022

Abstract
The dust extinction curves toward individual sight lines in M33 are derived for the first time with a sample of reddened O-type and B-type supergiants obtained from the Local Group Galaxies Survey (LGGS). The observed photometric data are obtained from the LGGS, PS1 Survey, UKIRT, PHATTER Survey, Galaxy Evolution Explorer, Swift/UVOT, and XMM-SUSS. We combine the intrinsic spectral energy distributions (SEDs) obtained from the ATLAS9 and Tlusty stellar model atmosphere extinguished by the model extinction curves from the silicate-graphite dust model to construct model SEDs. The extinction traces are distributed along the arms in M33, and the derived extinction curves cover a wide range of shapes (R

V
≈ 2–6), indicating the complexity of the interstellar environment and the inhomogeneous distribution of interstellar dust in M33. The average extinction curve with R

V
≈ 3.39 and dust size distribution

dn

/

da
∼

a

−
3.45

exp
(
−
a

/

0.25
)

is similar to that of the Milky Way but with a weaker 2175 Å bump and a slightly steeper rise in the far-UV band. The extinction in the V band of M33 is up to 2 mag, with a median value of A

V
≈ 0.43 mag. The multiband extinction values from the UV to IR bands are also predicted for M33, which will provide extinction corrections for future works. The method adopted in this work is also applied to other star-resolved galaxies (NGC 6822 and WLM), but only a few extinction curves can be derived because of the limited observations.
Can We Detect Coronal Mass Ejections through Asymmetries of Sun-as-a-star Extreme-ultraviolet Spectral Line Profiles?
Authors: Yang 杨 Zihao 子浩 , Tian 田 Hui 晖 , Bai Xianyong , Chen Yajie , Guo Yang , Zhu 朱 Yingjie 英杰 , Cheng Xin , Gao 高 Yuhang 宇航 , Xu 徐 Yu 昱 , Chen Hechao , Zhang Jiale 
Published: June 2022

Abstract
Coronal mass ejections (CMEs) are the largest-scale eruptive phenomena in the solar system. Associated with enormous plasma ejections and energy releases, CMEs have an important impact on the solar–terrestrial environment. Accurate predictions of the arrival times of CMEs at the Earth depend on precise measurements of their 3D velocities, which can be achieved by using simultaneous line-of-sight (LOS) and plane-of-sky (POS) observations. Besides the POS information from routine coronagraph and extreme-ultraviolet (EUV) imaging observations, spectroscopic observations could unveil the physical properties of CMEs, including their LOS velocities. We propose that spectral line asymmetries measured by Sun-as-a-star spectrographs can be used for routine detections of CMEs and estimations of their LOS velocities during their early propagation phases. Such observations can also provide important clues for the detection of CMEs on other solar-like stars. However, few studies have concentrated on whether we can detect CME signals and accurately diagnose CME properties through Sun-as-a-star spectral observations. In this work, we construct a geometric CME model and derive the analytical expressions for full disk-integrated EUV line profiles during CMEs. For different CME properties and instrumental configurations, the full disk-integrated line profiles are synthesized. We further evaluate the detectability and diagnostic potential of CMEs from the synthetic line profiles. Our investigations provide important constraints on the future design of Sun-as-a-star spectrographs for CME detections through EUV line asymmetries.
The Binary Black Hole Spin Distribution Likely Broadens with Redshift
Authors: Biscoveanu Sylvia , Callister Thomas A. , Haster Carl-Johan , Ng Ken K. Y. , Vitale Salvatore , Farr Will M. 
Published: June 2022

Abstract
The population-level distributions of the masses, spins, and redshifts of binary black holes (BBHs) observed using gravitational waves can shed light on how these systems form and evolve. Because of the complex astrophysical processes shaping the inferred BBH population, models allowing for correlations among these parameters will be necessary to fully characterize these sources. We hierarchically analyze the BBH population detected by LIGO and Virgo with a model allowing for correlations between the effective aligned spin and the primary mass and redshift. We find that the width of the effective spin distribution grows with redshift at 98.6% credibility. We determine this trend to be robust under the application of several alternative models and additionally verify that such a correlation is unlikely to be spuriously introduced using a simulated population. We discuss the possibility that this correlation could be due to a change in the natal black hole spin distribution with redshift.