adsabs/SciX_UAT_keywords huggingface dataset:
GRB 180720B: A GRB with Interesting Spectral Characteristics

The radiation mechanism and jet composition of gamma-ray bursts (GRBs) are still two important unresolved issues, and studying its energy spectrum characteristics can provide us with evidence. In this paper, we first use the smoothly broken power-law function (Band) and the cutoff power-law function to perform Bayesian time-resolved spectrum analysis on GRB 180720B and find these spectra can be well fitted. When the thermal component is added, approximately 40% of the resolution spectrum fitting statistics are significantly improved, indicating that there is a thermal spectral component in the burst. The thermal spectra are concentrated at the beginning and peak stage of the pulses. Therefore, the burst also supports that the GRB jet component transitions from material dominance to magnetic dominance. The values of the low-energy spectrum index α of the time-resolved spectra do not exceed the so-called synchrotron line of death, regardless of whether the thermal components are added or not, which indicates that the burst can be explained by synchrotron radiation. Moreover, we find that both α and Ep track the flux, but their tracking modes are different. We use the synchrotron model to fit these time-resolved spectra and find that these spectra can also be well fitted by the model. Furthermore, we find that both the electron spectrum index p and the magnetic field strength B track the flux and are positively correlated with the flux. Our results also show that the Band function can be explained by the synchrotron model in the Gamma-ray Burst Monitor energy range.

Keywords: gamma-ray bursts
The Effect of f(R, T) Modified Gravity on the Mass and Radius of Pulsar HerX1

Millisecond pulsars are the perfect testable to examine potential matter-geometry coupling and its physical consequences in the context of the recent Neutron Star Interior Composition Explorer discoveries. We apply the field equations of modified gravity, f(R, T) = R + α T, to a spherically symmetric spacetime, where R is the Ricci scalar, α is a dimensional parameter, and T is the matter of the geometry. Five unknown functions are present in the output system of differential equations, which consists of three equations. To close the system, we make explicit assumptions about the anisotropy and the radial metric potential, g rr . We then solve the output differential equations and derive the explicit forms of the components of the energy-momentum tensor, i.e., density, radial, and tangential pressures. We look into the possibility that all of the physical parameters in the star can be reexpressed in terms of α and the compactness parameters, C = 2 GM Rc-2. We show that, for a given mass, the size permitted by Einstein's general relativity is less due to the matter-geometry coupling in f(R, T). The validity of the hypothesis was validated by observations from an extra 21 pulsars. To achieve a surface density that is compatible with a neutron core at nuclear saturation density, the mass-radius curve enables masses up to 3.35M ⊙. We emphasize that although there is no assumption of an equation of state, the model fits well with a linear behavior. When comparing the surface densities of these 20 pulsars, we divided them into three groups. We show that these three groups are compatible with neutron cores.

Keywords: star formation; gravitation
Hardness Test of GRB 950830 as a Gravitationally Lensed Echo

Cumulative hardness comparisons are a simple but statistically powerful test for the presence of gravitational lensing in gamma-ray bursts (GRBs). Since gravitational lensing does not change photon energies, all source images should have the same spectra—and hence hardness. Applied to the recent claim that the two pulses in GRB 950830 are lensed images of the same pulse, the measured flux ratio between the two main pulses should be the same at all energies. After summing up all the counts in both of GRB 950830's two pulses in all four BATSE energy bands, it was found that in energy channel 3, the second pulse appears somewhat weak. In comparison with the other BATSE energy channels, the difference was statistically significant at above 90%. This model-independent test indicates that the case for GRB 950830 involving a gravitational lens may be intriguing—but should not be considered proven.

Keywords: gravitational lensing; gamma-ray bursts
Comparison of Different Tidal Disruption Event Light Curve Models with TiDE, a New Modular Open Source Code

A tidal disruption event (TDE) occurs when a supermassive black hole disrupts a nearby passing star by tidal forces. The subsequent fallback accretion of the stellar debris results in a luminous transient outburst. Modeling the light curve of such an event may reveal important information, for example the mass of the central black hole. This paper presents the TiDE software based on semi-analytic modeling of TDEs. This object-oriented code contains different models for the accretion rate and the fallback timescale ${t}_{\min }$ . We compare the resulting accretion rates to each other and with hydrodynamically simulated ones and find convincing agreement for full disruptions. We present a set of parameters estimated with TiDE for the well-observed TDE candidate AT2019qiz, and compare our results with those given by the MOSFiT code. Most of the parameters are in reasonable agreement, except for the mass and the radiative efficiency of the black hole, both of which depend heavily on the adopted fallback accretion rate.

Keywords: supermassive black holes; accretion; tidal disruption
Transverse MHD Waves as Signatures of Braiding-induced Magnetic Reconnection in Coronal Loops

A major coronal heating theory based on magnetic reconnection relies on the existence of braided magnetic field structures in the corona. In this small-angle reconnection scenario, numerical simulations indicate that the reconnected magnetic field lines are driven sideways by magnetic tension and can overshoot from their new rest position, thereby leading to low-amplitude transverse MHD waves. This provides an efficient mechanism for transverse MHD wave generation, and the direct causality also constitutes substantial evidence of reconnection from braiding. However, this wave-generation mechanism has never been directly observed. Recently, the telltale signature of small-angle reconnection in a sheared coronal structure has been identified through nanojets, which are small, short-lived, and fast jetlike bursts in the nanoflare range transverse to the guide field. We present for the first time Interface Region Imaging Spectrograph and Solar Dynamics Observatory observations of transverse MHD waves in a coronal loop that directly result from braiding-induced reconnection. The reconnection is identified by the presence of nanojets at the loop apex that release nanoflare-range energy. We find that the oscillations have an energy flux on the order of 106-108 erg cm-2 s-1, which is within the budget to power active region loops. The estimated kinetic and thermal energy from the nanojets is also sufficient to power the transverse waves and sustain the observed heating at the loop apex. This discovery provides major support to (a) existing theories that transverse MHD waves can be a signature of reconnection, (b) the existence of braiding in coronal structures, and (c) the coronal reconnection scenario identified by nanojets.

Keywords: the sun; solar corona; solar magnetic fields; solar coronal waves; magnetohydrodynamics
Machine Learning Detects Multiplicity of the First Stars in Stellar Archaeology Data

In unveiling the nature of the first stars, the main astronomical clue is the elemental compositions of the second generation of stars, observed as extremely metal-poor (EMP) stars, in the Milky Way. However, no observational constraint was available on their multiplicity, which is crucial for understanding early phases of galaxy formation. We develop a new data-driven method to classify observed EMP stars into mono- or multi-enriched stars with support vector machines. We also use our own nucleosynthesis yields of core-collapse supernovae with mixing fallback that can explain many of the observed EMP stars. Our method predicts, for the first time, that 31.8% ± 2.3% of 462 analyzed EMP stars are classified as mono-enriched. This means that the majority of EMP stars are likely multi-enriched, suggesting that the first stars were born in small clusters. Lower-metallicity stars are more likely to be enriched by a single supernova, most of which have high carbon enhancement. We also find that Fe, Mg. Ca, and C are the most informative elements for this classification. In addition, oxygen is very informative despite its low observability. Our data-driven method sheds a new light on solving the mystery of the first stars from the complex data set of Galactic archeology surveys.

Keywords: population iii stars; population ii stars; milky way formation; support vector machine
The Hα Luminosity Function of Galaxies at z 4.5

We present the Hα luminosity function (LF) derived from a large sample of Lyman break galaxies at z ~ 4.5 over the GOODS-South and North fields. This study makes use of the new, full-depth Spitzer/IRAC [3.6] and [4.5] imaging from the GOODS Re-ionization Era wide-Area Treasury from the Spitzer program. The Hα flux is derived from the offset between the continuum flux estimated from the best-fit spectral energy distribution, and the observed photometry in IRAC [3.6]. From these measurements, we build the Hα LF and study its evolution providing the best constraints of this property at high redshift, where spectroscopy of Hα is not yet available. Schechter parameterizations of the Hα LF show a decreasing evolution of Φ∗ with redshift, increasing evolution in L ∗, and no significant evolution in the faint-end slope at high z. We find that star formation rates (SFRs) derived from Hα are higher than those derived from the rest-frame UV for low SFR galaxies but the opposite happens for the highest SFRs. This can be explained by lower mass galaxies (also lower SFR) having, on average, rising star formation histories (SFHs), while at the highest masses the SFHs may be declining. The SFR function is steeper, and because of the excess SFR(Hα) compared to SFR(UV) at low SFRs, the SFR density estimated from Hα is higher than the previous estimates based on UV luminosities.

Keywords: galaxy evolution; galaxy formation; high-redshift galaxies
Dissecting the Strong-lensing Galaxy Cluster MS 0440.5+0204. II. New Optical Spectroscopic Observations in a Wider Area and Cluster Dynamical State

We present an optical study of the strong-lensing galaxy cluster MS 0440.5+0204 at z = 0.19593, based on CFHT/MegaCam g', r' photometry and GMOS/Gemini and CFHT/MOS/SIS spectroscopy in a broader area than previous works. We have determined new spectroscopic redshifts for the most prominent gravitational arcs surrounding the central galaxy in the cluster. The new redshifts and the information provided by the photometric catalog allow us to perform a detailed weak- and strong-lensing mass reconstruction of the cluster. The large number of member galaxies and the area covered by our observations allow us to estimate more accurately the velocity dispersion and mass of the cluster and to examine in detail the nature of the cluster and surrounding structures. The dynamical mass is in good agreement with the mass inferred from the lensing analysis and X-ray estimates. About 68% of the galaxies are located in the inner ≲0.86 ${h}_{70}^{-1}$ Mpc region of the cluster. The galaxy redshift distribution in the inner region of the cluster shows a complex structure with at least three substructures along the line of sight. Other substructures are also identified in the galaxy density map and in the weak-lensing mass map. The member galaxies in the northeast overdensity are distributed in a filament between the clusters MS 0440.5+0204 and ZwCL 0441.1+0211, suggesting that these two structures might be connected. MS 0440.5+0204 appears to be dynamically active, with a cluster core that is likely experiencing a merging process, and with other nearby groups at projected distances of ≲1 ${h}_{70}^{-1}$ Mpc that could be being accreted by the cluster.

Keywords: galaxy clusters; redshift surveys; gravitational lensing
The Opposite Behaviors of Proton and Electron Temperatures in Relation to Solar Wind Magnetic Energy: Parker Solar Probe Observations

Solar wind heating is an outstanding issue that has been discussed for decades. Research on the connection between solar wind particle temperatures and turbulence may provide insight into this issue. Based on Parker Solar Probe observations, this paper investigates the properties of solar wind proton and electron temperatures in relation to turbulent magnetic energy, via the calculation of correlation coefficients (CCs) between particle temperatures and magnetic energy. The calculations are regulated by the spatial scale, plasma beta (β), and the angle between the solar wind velocity and background magnetic field, where the plasma beta is the ratio of plasma thermal to magnetic pressure. Results show that the correlation between proton temperature and magnetic energy is positive and can be strong with a CC exceeding 0.8. The strong correlation preferentially occurs at ion scales, with the wind velocity and background magnetic field quasi-perpendicular and over a wide beta range (β < 3.0). On the other hand, the correlation between electron temperature and magnetic energy is commonly negative, often with an intermediate or negligible CC, accordingly. The CC with an amplitude up to 0.8 can arise at larger scales with the wind velocity and background magnetic field quasi-(anti)parallel and in the low-beta case (β < 0.6). The implication of these findings on the physics of turbulent heating in the solar wind is discussed.

Keywords: solar wind; interplanetary turbulence; solar coronal heating; space plasmas; plasma physics
The Power Spectra of Polarized, Dusty Filaments

We develop an analytic model for the power spectra of polarized filamentary structures as a way to study the Galactic polarization foreground to the cosmic microwave background. Our approach is akin to the cosmological halo-model framework, and reproduces the main features of the Planck 353 GHz power spectra. We model the foreground as randomly oriented, three-dimensional, spheroidal filaments, accounting for their projection onto the sky. The main tunable parameters are the distribution of filament sizes, the physical aspect ratio of filaments, and the dispersion of the filament axis around the local magnetic field direction. The abundance and properties of filaments as a function of size determine the slopes of the foreground power spectra, as we show via scaling arguments. The filament aspect ratio determines the ratio of B-mode power to E-mode power, and specifically reproduces the Planck-observed dust ratio of one-half when the short axis is roughly one-fourth the length of the long axis. Filament misalignment to the local magnetic field determines the TE cross-correlation, and to reproduce Planck measurements we need a (three-dimensional) misalignment angle with an rms dispersion of about 50°. These parameters are not sensitive to the particular filament density profile. By artificially skewing the distribution of the misalignment angle, this model can reproduce the Planck-observed (and parity-violating) TB correlation. The skewing of the misalignment angle necessary to explain TB will cause a yet-unobserved, positive EB dust correlation, a possible target for future experiments.

Keywords: cosmic microwave background radiation; interstellar medium
Constraining Nucleosynthesis in Neutrino-driven Winds: Observations, Simulations, and Nuclear Physics

A promising astrophysical site to produce the lighter heavy elements of the first r-process peak (Z = 38 - 47) is the moderately neutron-rich (0.4 < Y e < 0.5) neutrino-driven ejecta of explosive environments, such as core-collapse supernovae and neutron star mergers, where the weak r-process operates. This nucleosynthesis exhibits uncertainties from the absence of experimental data from (α, xn) reactions on neutron-rich nuclei, which are currently based on statistical model estimates. In this work, we report on a new study of the nuclear reaction impact using a Monte Carlo approach and improved (α, xn) rates based on the Atomki-V2 α optical model potential. We compare our results with observations from an up-to-date list of metal-poor stars with [Fe/H] < -1.5 to find conditions of the neutrino-driven wind where the lighter heavy elements can be synthesized. We identified a list of (α, xn) reaction rates that affect key elemental ratios in different astrophysical conditions. Our study aims to motivate more nuclear physics experiments on (α, xn) reactions using the current and new generation of radioactive beam facilities and also more observational studies of metal-poor stars.

Keywords: core-collapse supernovae; nuclear astrophysics; nucleosynthesis; r-process; nuclear reaction cross sections
Magnetic Field Effects on the Vishniac Overstability in Scaled Radiative Blast Waves

We report experimental results on the stability of a magnetized laser-launched blast wave scaled to simulate a late-stage supernova remnant. We extend previous results to show the effect of a dynamically significant magnetic field on the spatial mode spectrum of the instability. We find that magnetic fields reduce instability growth, possibly influencing turbulent feedback to the interstellar medium.

Keywords: supernova remnants; supernova dynamics; laboratory astrophysics
Deciphering the Kinematic Structure of the Small Magellanic Cloud through Its Red Giant Population

We present a new kinematic model for the Small Magellanic Cloud (SMC), using data from the Gaia Data Release 2 catalog. We identify a sample of astrometrically well-behaved red giant (RG) stars belonging to the SMC and cross-match with publicly available radial velocity (RV) catalogs. We create a 3D spatial model for the RGs, using RR Lyrae for distance distributions, and apply kinematic models with varying rotation properties and a novel tidal expansion prescription to generate mock proper motion (PM) catalogs. When we compare this series of mock catalogs to the observed RG data, we find that a combination of moderate rotation (with a magnitude of ∼10-20 km s-1 at 1 kpc from the SMC center, inclination between ∼50 and 80°, and a predominantly north-to-south line-of-nodes position angle of ∼180°) and tidal expansion (with a scaling of ∼10 km s-1 kpc-1) is required to explain the PM signatures. The exact best-fit parameters depend somewhat on whether we assess only the PMs or include the RVs as a qualitative check, leaving some tension remaining between the PM and RV conclusions. In either case, the parameter space preferred by our model is different from previously inferred rotational geometries, including from the SMC H I gas, and from the RG RV-only analyses and new SMC PM analyses, which conclude that a rotation signature is not detectable. Taken together this underscores the need to treat the SMC as a series of different populations with distinct kinematics.

Keywords: proper motions; stellar motion; galaxy kinematics; galaxy dynamics; small magellanic cloud; galaxy interactions; magellanic clouds
Deep Large Binocular Camera r-band Observations of the GOODS-N Field

We obtained 838 Sloan r-band images (~28 hr) of the GOODS-North field with the Large Binocular Camera (LBC) on the Large Binocular Telescope in order to study the presence of extended, low surface brightness features in galaxies and investigate the trade-off between image depth and resolution. The individual images were sorted by effective seeing, which allowed for optimal resolution and optimal depth mosaics to be created with all images with seeing FWHM < 0.″9 and FWHM < 2.″0, respectively. Examining bright galaxies and their substructure as well as accurately deblending overlapping objects requires the optimal resolution mosaic, while detecting the faintest objects possible (to a limiting magnitude of m AB ~ 29.2 mag) requires the optimal depth mosaic. The better surface brightness sensitivity resulting from the larger LBC pixels, compared to those of extant WFC3/UVIS and ACS/WFC cameras aboard the Hubble Space Telescope allows for unambiguous detection of both diffuse flux and very faint tidal tails. Azimuthally-averaged radial surface brightness profiles were created for the 360 brightest galaxies in each of the two mosaics. On average, these profiles showed minimal difference between the optimal resolution and optimal depth surface brightness profiles. However, ≲15% of the profiles show excess flux in the galaxy outskirts down to surface brightness levels of ${\mu }_{r}^{\mathrm{AB}}$ ≃ 31 mag arcsec-2. This is relevant to Extragalactic Background Light (EBL) studies as diffuse light in the outer regions of galaxies are thought to be a major contribution to the EBL. While some additional diffuse light exists in the optimal depth profiles compared to the shallower, optimal resolution profiles, we find that diffuse light in galaxy outskirts is a minor contribution to the EBL overall in the r-band.

Keywords: astronomical techniques; extragalactic astronomy
Properties of the KISS Green Pea Galaxies

Green peas (GPs) are a class of extreme star-forming galaxies (SFGs) at intermediate redshifts, originally discovered via color selection using multifilter, wide-field survey imaging data. They are commonly thought of as being analogs of high-redshift Lyα-emitting galaxies. The defining characteristic of GP galaxies is a high-excitation nebular spectrum with very large equivalent width lines, leading to the recognition that GP-like galaxies can also be identified in samples of emission-line galaxies. Here we compare the properties a sample of [O III]-selected SFGs (z = 0.29-0.41) from the KPNO International Spectroscopic Survey (KISS) with the color-selected GPs. We find that the KISS [O III]-selected galaxies overlap with the parameter space defined by the color-selected GPs; the two samples appear to be drawn from the same population of objects. We compare the KISS GPs with the full Hα-selected KISS SFG sample (z < 0.1) and find that they are extreme systems. Many appear to be young systems at their observed look-back times (3-4 Gyr), with more than 90% of their rest-frame B-band luminosity coming from the starburst population. We compute the volume density of the KISS red (KISSR) GPs at z = 0.29-0.41 and find that they are extremely rare objects. We do not see galaxies as extreme as the KISSR GPs in the local universe, although we recognize several lower-luminosity systems at z < 0.1.

Keywords: emission line galaxies; galaxy abundances; star formation; starburst galaxies; galaxy evolution