adsabs/SciX_UAT_keywords huggingface dataset:
Testing the Polarization of Gravitational-wave Background with the LISA-TianQin Network

While general relativity predicts only two tensor modes for gravitational-wave (GW) polarization, general metric theories of gravity allow for up to four additional modes, including two vector and two scalar modes. Observing the polarization modes of GWs could provide a direct test of the modified gravity. The stochastic GW background (SGWB), which can be detected by space-based laser-interferometric detectors at design sensitivity, will provide an opportunity to directly measure alternative polarization. In this paper, we investigate the performance of the LISA-TianQin network for detecting alternative polarizations of stochastic backgrounds, and propose a method to separate different polarization modes. First, we generalize the small antenna approximation to compute the overlap reduction functions for the SGWB with arbitrary polarization, which is suitable for any time-delay interferometry combination. Then we analyze the detection capability of LISA-TianQin for the SGWB with different polarizations. Based on the orbital characteristics of LISA-TianQin, we propose a method to distinguish different polarization modes from their mixed data. Finally, simulation tests are performed to verify the effectiveness of the method. The results of the simulations demonstrate that LISA-TianQin, when employing our proposed method, has the ability to differentiate between various polarization modes, with a specific emphasis on the ability to distinguish between the breathing and longitudinal modes.

Keywords: gravitational waves
Cosmic Neutrinos from Temporarily Gamma-suppressed Blazars

Despite the uncovered association of a high-energy neutrino with the apparent flaring state of blazar TXS 0506+056 in 2017, the mechanisms leading to astrophysical particle acceleration and neutrino production are still uncertain. Recent studies found that when transparent to γ-rays, γ-flaring blazars do not have the opacity for protons to produce neutrinos. Here we present observational evidence for an alternative explanation, in which γ-ray emission is suppressed during efficient neutrino production. A large proton and target photon density helps produce neutrinos while temporarily suppressing the observable γ-emission due to a large γγ opacity. We show that the Fermi-LAT γ-flux of blazar PKS 1502+106 was at a local minimum when IceCube recorded the coincident high-energy neutrino IC-190730A. Using data from the OVRO 40 m Telescope, we find that radio emission from PKS 1502+106 at the time period of the coincident neutrino IC-190730A was in a high state, in contrast to earlier time periods when radio and γ fluxes are correlated for both low and high states. This points to an active outflow that is γ-suppressed at the time of neutrino production. We find similar local γ-suppression in other blazars, including in MAGIC's TeV flux of TXS 0506+056 and Fermi-LAT's flux of blazar PKS B1424-418 at the time of coincident IceCube neutrino detections. Using temporary γ-suppression, neutrino-blazar coincidence searches could be substantially more sensitive than previously assumed, enabling the identification of the origin of IceCube's diffuse neutrino flux possibly with already existing data.

Keywords: galactic and extragalactic astronomy; active galactic nuclei; blazars
Observations of GRB 230307A by TESS

We present the Transiting Exoplanet Survey Satellite (TESS) light curve of GRB 230307A. We find two distinct components: a bright, prompt optical component at the time of the Fermi observation that peaked at TESS magnitude 14.49 ± 0.05 (averaged over 200 s), followed by a gradual rise and fall over 0.5 day, likely associated with the afterglow, that peaked at 17.65 ± 0.06 mag. The prompt component is observed in a single 200 s Full Frame Image and was undetectable in the next TESS image (T mag > 17.79). Assuming that the onset of the optical transient was coincident with the gamma-ray emission, the prompt emission lasted less than 73.6 s, which implies the true peak was actually brighter than T mag = 13.40. We also fit parametric models to the afterglow to characterize its shape. The TESS TICA light curve can be retrieved at https://tess.mit.edu/public/tesstransients/light_curves/lc_grb230307A_cleaned.txt.

Keywords: gamma-ray bursts; gamma-ray transient sources
High-resolution Spectral Discriminants of Ocean Loss for M-dwarf Terrestrial Exoplanets

In the near future, extremely large ground-based telescopes may conduct some of the first searches for life beyond the solar system. High spectral resolution observations of reflected light from nearby exoplanetary atmospheres could be used to search for the biosignature oxygen. However, while Earth's abundant O2 is photosynthetic, early ocean loss may also produce high atmospheric O2 via water vapor photolysis and subsequent hydrogen escape. To explore how to use spectra to discriminate between these two oxygen sources, we generate high-resolution line-by-line synthetic spectra of both a habitable Earth-like and post-ocean-loss Proxima Centauri b. We examine the strength and profile of four bands of O2 from 0.63 to 1.27 μm, and quantify their relative detectability. We find that 10 bar O2 post-ocean-loss atmospheres have strong suppression of oxygen bands, and especially the 1.27 μum band. This suppression is due to additional strong, broad O2-O2 collisionally induced absorption (CIA) generated in these more massive O2 atmospheres, which is not present for the smaller amounts of oxygen generated by photosynthesis. Consequently, any detection of the 1.27 μm band in reflected light indicates lower Earth-like O2 levels, which suggests a likely photosynthetic origin. However, the 0.69 μm O2 band is relatively unaffected by O2-O2 CIA, and the presence of an ocean-loss high-O2 atmosphere could be inferred via detection of a strong 0.69 μm O2 band, and a weaker or undetected 1.27 μm band. These results provide a strategy for observing and interpreting O2 in exoplanet atmospheres, that could be considered by future ground-based telescopes.

Keywords: extrasolar rocky planets; high resolution spectroscopy; exoplanet atmospheres; exoplanet atmospheric composition
Gastro Library. I. The Simulated Chemodynamical Properties of Several Gaia-Sausage-Enceladus-like Stellar Halos

The Milky Way (MW) stellar halo contains relics of ancient mergers that tell the story of our galaxy's formation. Some of them are identified due to their similarity in energy, actions, and chemistry, referred to as the "chemodynamical space," and are often attributed to distinct merger events. It is also known that our galaxy went through a significant merger event that shaped the local stellar halo during its first billion years. Previous studies using N-body only and cosmological hydrodynamical simulations have shown that such a single massive merger can produce several "signatures" in the chemodynamical space, which can potentially be misinterpreted as distinct merger events. Motivated by these, in this work we use a subset of the GASTRO library, which consists of several smoothed particle hydrodynamics+N-body models of a single accretion event in a MW-like galaxy. Here, we study models with orbital properties similar to the main merger event of our galaxy and explore the implications to known stellar halo substructures. We find that (i) supernova feedback efficiency influences the satellite's structure and orbital evolution, resulting in distinct chemodynamical features for models with the same initial conditions; (ii) very retrograde high-energy stars are the most metal-poor of the accreted dwarf galaxy and could be misinterpreted as a distinct merger; (iii) the most bound stars are more metal-rich in our models, the opposite of what is observed in the MW, suggesting a secondary massive merger; and, finally, (iv) our models can reconcile other known apparently distinct substructures to a unique progenitor.

Keywords: milky way dynamics; milky way formation; milky way stellar halo; hydrodynamical simulations
Improving Cosmological Constraints from Galaxy Cluster Number Counts with CMB-cluster-lensing Data: Results from the SPT-SZ Survey and Forecasts for the Future

We show the improvement to cosmological constraints from galaxy cluster surveys with the addition of cosmic microwave background (CMB)-cluster lensing data. We explore the cosmological implications of adding mass information from the 3.1σ detection of gravitational lensing of the CMB by galaxy clusters to the Sunyaev-Zel'dovich (SZ) selected galaxy cluster sample from the 2500 deg2 SPT-SZ survey and targeted optical and X-ray follow-up data. In the ΛCDM model, the combination of the cluster sample with the Planck power spectrum measurements prefers ${\sigma }_{8}{\left({{\rm{\Omega }}}_{m}/0.3\right)}^{0.5}=0.831\pm 0.020$ . Adding the cluster data reduces the uncertainty on this quantity by a factor of 1.4, which is unchanged whether the 3.1σ CMB-cluster lensing measurement is included or not. We then forecast the impact of CMB-cluster lensing measurements with future cluster catalogs. Adding CMB-cluster lensing measurements to the SZ cluster catalog of the ongoing SPT-3G survey is expected to improve the expected constraint on the dark energy equation of state w by a factor of 1.3 to σ(w) = 0.19. We find the largest improvements from CMB-cluster lensing measurements to be for σ 8, where adding CMB-cluster lensing data to the cluster number counts reduces the expected uncertainty on σ 8 by respective factors of 2.4 and 3.6 for SPT-3G and CMB-S4.

Keywords: cosmology; sigma8
The Changing-look Blazar B2 1420+32

Blazars are active galactic nuclei with their relativistic jets pointing toward the observer, comprising two major subclasses, flat-spectrum radio quasars (FSRQs) and BL Lac objects. We present multiwavelength photometric and spectroscopic monitoring observations of the blazar B2 1420+32, focusing on its outbursts in 2018-2020. Multiepoch spectra show that the blazar exhibited large-scale spectral variability in both its continuum and line emission, accompanied by dramatic gamma-ray and optical variability by factors of up to 40 and 15, respectively, on week to month timescales. Over the last decade, the gamma-ray and optical fluxes increased by factors of 1500 and 100, respectively. B2 1420+32 was an FSRQ with broad emission lines in 1995. Following a series of flares starting in 2018, it transitioned between BL Lac and FSRQ states multiple times, with the emergence of a strong Fe pseudocontinuum. Two spectra also contain components that can be modeled as single-temperature blackbodies of 12,000 and 5200 K. Such a collection of "changing-look" features has never been observed previously in a blazar. We measure gamma-ray-optical and interband optical lags implying emission-region separations of less than 800 and 130 gravitational radii, respectively. Since most emission-line flux variations, except the Fe continuum, are within a factor of 2-3, the transitions between FSRQ and BL Lac classifications are mainly caused by the continuum variability. The large Fe continuum flux increase suggests the occurrence of dust sublimation releasing more Fe ions in the central engine and an energy transfer from the relativistic jet to subrelativistic emission components.

Keywords: active galactic nuclei; blazars; radio loud quasars; black hole physics; quasars; time domain astronomy
Into the UV: The Atmosphere of the Hot Jupiter HAT-P-41b Revealed

For solar system objects, ultraviolet spectroscopy has been critical in identifying sources of stratospheric heating and measuring the abundances of a variety of hydrocarbon and sulfur-bearing species, produced via photochemical mechanisms, as well as oxygen and ozone. To date, fewer than 20 exoplanets have been probed in this critical wavelength range (0.2-0.4 μm). Here we use data from Hubble's newly implemented WFC3 UVIS G280 grism to probe the atmosphere of the hot Jupiter HAT-P-41b in the ultraviolet through optical in combination with observations at infrared wavelengths. We analyze and interpret HAT-P-41b's 0.2-5.0 μm transmission spectrum using a broad range of methodologies including multiple treatments of data systematics as well as comparisons with atmospheric forward, cloud microphysical, and multiple atmospheric retrieval models. Although some analysis and interpretation methods favor the presence of clouds or potentially a combination of Na, VO, AlO, and CrH to explain the ultraviolet through optical portions of HAT-P-41b's transmission spectrum, we find that the presence of a significant H- opacity provides the most robust explanation. We obtain a constraint for the abundance of H-, $\mathrm{log}({{\rm{H}}}^{-})=-8.65\pm 0.62$ , in HAT-P-41b's atmosphere, which is several orders of magnitude larger than predictions from equilibrium chemistry for a ∼1700-1950 K hot Jupiter. We show that a combination of photochemical and collisional processes on hot hydrogen-dominated exoplanets can readily supply the necessary amount of H- and suggest that such processes are at work in HAT-P-41b and the atmospheres of many other hot Jupiters.

Keywords: exoplanet atmospheres; observational astronomy; exoplanet atmospheric composition; spectroscopy
Spatial Power Spectral Analysis of the Suzaku X-Ray Background

Power spectra of spatial fluctuations of X-ray emission may impose constraints on the origins of the emission independent of that from the energy spectra. We generated spatial power spectrum densities (PSDs) of blank X-ray skies observed with the Suzaku X-ray observatory utilizing the modified Δ-variance method. Using the total measured count rate as the diagnostic tool, we found that a model consisting of the sum of two components, one for the unresolved faint point sources and one for the uniform flat-field emission, can represent well the observed PSD in three different energy bands (0.2-0.5, 0.5-2, and 2-10 keV); only an upper limit is obtained for the latter component in 2-10 keV. X-ray counting rates corresponding to the best-fit PSD model functions and diffuse emission fractions were estimated, and we confirmed that the sum of the counting rates of two model components is consistent with those actually observed with the detector for all energy bands. The ratio of the flat-field counting rate to the total in 0.5-2 keV, however, is significantly larger than the diffuse emission fraction estimated from the model fits of energy spectra. We discussed that this discrepancy can be reconciled by systematic effects in the PSD and energy spectrum analyses. The present study demonstrates that the spatial power spectrum analysis is powerful in constraining the origins of the X-ray emission.

Keywords: interstellar medium; diffuse x-ray background; x-ray sources; warm-hot intergalactic medium; high energy astrophysics; large-scale structure of the universe
Fermi-LAT Detection of the Supernova Remnant G312.4-0.4 in the Vicinity of 4FGL J1409.1-6121e

Gamma-ray emission provides constraints on the nonthermal radiation processes at play in astrophysical particle accelerators. This allows both the nature of accelerated particles and the maximum energy that they can reach to be determined. Notably, it remains an open question to what extent supernova remnants contribute to the sea of Galactic cosmic rays. In the Galactic plane, at around 312° of Galactic longitude, Fermi-LAT observations show an extended source (4FGL J1409.1-6121e) around five powerful pulsars. This source is described by one large disk of 0.°7 radius with a high significance of 45σ in the 4FGL-DR3 catalog. Using 14 yr of Fermi-LAT observations, we revisited this region with a detailed spectro-morphological analysis in order to disentangle its underlying structure. Three sources have been distinguished, including the supernova remnant G312.4-0.4 whose gamma-ray emission correlates well with the shell observed at radio energies. The hard spectrum detected by the LAT, extending up to 100 GeV without any sign of a cutoff, is well reproduced by a purely hadronic model.

Keywords: gamma-ray astronomy; supernova remnants; pulsar wind nebulae
Black Hole Hyperaccretion in Collapsars. II. Gravitational Waves

As progenitors of gamma-ray bursts (GRBs), the core collapse of massive stars and the coalescence of compact object binaries are believed to be powerful sources of gravitational waves (GWs). In the collapsar scenario, a rotating stellar-mass black hole (BH) surrounded by a hyperaccretion disk might be active in the center of a massive collapsar, which is one of the plausible central engines of long GRBs. Such a BH hyperaccretion disk would be in a state of a neutrino-dominated accretion flow (NDAF) at the initial stage of the accretion process; meanwhile, the jets attempt to break out from the envelope and circumstellar medium to power GRBs. In addition to collapsars, BH hyperaccretion systems are important sources of neutrinos and GWs. In this paper, we investigate the GW emission generated by the anisotropic neutrino emission from NDAFs in collapsar scenarios. As the results indicate, the typical frequency of GWs is ∼1-100 Hz, and the masses and metallicities of the progenitor stars have slight effects on the GW strains. The GWs from NDAFs might be detected by operational or planned detectors at a distance of 10 kpc. Moreover, comparisons of the detectable GWs from collapsars, NDAFs, and GRB jets (internal shocks) are displayed. By combining the electromagnetic counterparts, neutrinos, and GWs, one may constrain the characteristics of collapsars and central BH accretion systems.

Keywords: accretion; stellar mass black holes; neutrino astronomy; core-collapse supernovae; gravitational waves; gamma-ray bursts; relativistic jets
Global Energetics of Solar Flares. XII. Energy Scaling Laws

In this study we test 18 versions of five fundamental energy scaling laws that operate in large solar flares. We express scaling laws in terms of the magnetic potential field energy Ep, the mean potential field strength Bp, the free energy Efree, the dissipated magnetic flare energy Ediss, the magnetic length scale L, the thermal length scale Lth, the mean helically twisted flux tube radius R, the sunspot radius r, the emission-measure-weighted flare temperature Te, the electron density ne, and the total emission measure EM, measured from a data set of 173 GOES M- and X-class flare events. The five categories of physical scaling laws include (i) a scaling law of the potential field energy, (ii) a scaling law for helical twisting, (iii) a scaling law for Petschek-type magnetic reconnection, (iv) the Rosner-Tucker-Vaiana scaling law, and (v) the Shibata-Yokoyama scaling law. We test the self-consistency of these theoretical scaling laws with observed parameters by requiring two criteria: a cross-correlation coefficient of CCC > 0.5 between the theoretically predicted scaling laws and observed values, and a linear regression fit with a slope of α ≈ 1 within one standard deviation σ. These two criteria enable us (i) to corroborate some existing (or modified) scaling laws, (ii) to reject other scaling laws that are not consistent with the observations, (iii) to probe the dimensionality of flare geometries, and (iv) to predict various energy parameters based on tested scaling laws.

Keywords: solar flares
The Parameter-free Finger-of-God Model and Its Application to 21 cm Intensity Mapping

Using the galaxy catalog built from ELUCID N-body simulation and the semianalytical galaxy formation model, we have built a mock H I intensity mapping map. We have implemented the Finger-of-God (FoG) effect in the map by considering the galaxy H I gas velocity dispersion. By comparing the H I power spectrum in redshift space with a measurement from the IllustrisTNG simulation, we have found that the FoG effect can explain the discrepancy between current mock maps built from the N-body simulation and the IllustrisTNG simulation. Then we built a parameter-free FoG model and a shot-noise model to calculate the H I power spectrum. We found that our model can accurately fit both the monopole and quadrupole moments of the H I matter power spectrum. Our approach to building the mock H I intensity map and the parameter-free FoG model will be useful for upcoming 21 cm intensity mapping experiments, such as CHIME, Tianlai, BINGO, FAST, and SKA. It is also vital for studying nonlinear effects in 21 cm intensity mapping.

Keywords: line intensities; large-scale structure of the universe
Rovibrational Transitions in HCl due to Collisions with H2: Spin-free and Hyperfine-resolved Transitions

Hydrogen chloride (HCl) is a key repository of chlorine in the interstellar medium. Accurate determinations of its abundance are critical to assessing the chlorine elemental abundance and constraining stellar nucleosynthesis models. To aid in modeling recent and future observations of HCl rovibrational spectra, we present cross sections and rate coefficients for collisions between HCl and molecular hydrogen. Transitions between rovibrational states of HCl are considered for temperatures ranging from 10 to 3000 K. Cross sections are computed using a full dimensional quantum close-coupling (CC) method and a reduced dimensionality coupled-states (CS) approach. The CS results, benchmarked against the CC results, are used with a recoupling approach to calculate hyperfine-resolved rate coefficients for rovibrational transitions of HCl induced by H2. The rate coefficients will allow for a better determination of the HCl abundance in the interstellar medium and an improved understanding of interstellar chlorine chemistry. We demonstrate the utility of the new rate coefficients in a nonthermodynamic equilibrium radiative transfer model applied to observations of HCl rovibrational transitions in a circumstellar shell.

Keywords: molecular physics; small molecules; collision physics; de-excitation rates; molecular data