Astronomical Informant

2022-06-24 09:53:23 ATel 15464: KITS Spectroscopic Classification of AT 2022mxv as a Type II SN with Keck II + NIRES
https://www.astronomerstelegram.org/?read=15464

We report a classification of AT 2022mxv from spectroscopic observations with the NIRES spectrograph on the Keck II telescope, made on 2022 Jun 22 UT as part of the Keck Infrared Transient Survey (KITS), a NASA Keck Strategic Mission Support program. ... Aprire / Come

2022-06-24 05:37:00 arXiv:We discuss cosmology based on the cuscuton gravity theory to resolve the anomaly of the observational $^4$He abundance reported by the EMPRESS collaboration. We find that the gravitational constant $G_{\rm cos}$ in Friedmann equation should be smaller than the Newton's constant ${G_{\rm N}}$ such that ${\Delta G_{\rm N}}/{G_{\rm N}} \equiv (G_{\rm cos}-G_{\rm N})/{G_{\rm N}} = -0.086_{-0.028}^{+0.026} \quad(68 \% \text { C.L. })$ in terms of big-bang nucleosynthesis, which excludes ${\Delta G_{\rm N}}=0$ at more than 95~$\% \text { C.L. }$ To fit the data, we obtain a negative mass squared of a non-dynamical scalar field with the Planck-mass scale as $\sim - {\cal O}(1) {M_{\rm PL}^2} ({\mu}/{0.5 M_{\rm PL}})^{4}$ with the cuscuton mass parameter $\mu$. This fact could suggest the need for modified gravity theories such as the cuscuton gravity theory with a quadratic potential, which can be regarded as the low-energy Ho\v{r}ava-Lifshitz gravity, and might give a hint of quantum gravity.

via astro-ph updates on arXiv.org https://ift.tt/2zDbYIX Aprire / Come

2022-06-24 05:36:59 arXiv:We study the diffuse background free-free emission induced in dark matter halos. Since dark matter halos host ionized thermal plasma, they are an important source of the cosmological free-free emission. We evaluate the global background intensity and anisotropy of this free-free emission. We show that the dominant contribution comes from dark matter halos with a mass close to the Jeans mass, $M_{\mathrm{halo}}\sim 10^{10} M_\odot$, around the redshift $z \sim 1$. Therefore, the intensity of the free-free emission is sensitive to the small-scale curvature perturbations that form such small-mass dark matter halos. Considering the blue-tilted curvature perturbations, we find that the free-free emission signal is modified by $\sim 25 \%$ even in the parameter set of the spectral index and the running, which is consistent with the recent Planck result. However, our obtained intensity of the global and anisotropic free-free emission is smaller than the ten percent level of the observed free-free emission, which is dominated by the Galactic origin. Therefore, the measurement of the cosmological free-free signals has the potential to provide more stringent constraints on the abundance of small-mass dark matter halos and the curvature perturbations including the spectral index and the running, while carefully removing the Galactic free-free emission is required through the multifrequency radio observation or the cross-correlation study with the galaxy surveys or 21-cm intensity map.

via astro-ph updates on arXiv.org https://ift.tt/aCe8fG7 Aprire / Come

2022-06-24 05:36:58 arXiv:We explore the suggestion that the neutron lifetime puzzle might be resolved by neutrons decaying into dark matter through the process, n \rightarrow \chi\chi\chi, with \chi having a mass one third of that of the neutron. In particular, we examine the consequences of such a decay mode for the properties of neutron stars. Unlike an earlier suggested decay mode, in order to satisfy the constraints on neutron star mass and tidal deformability, there is no need for a strong repulsive force between the dark matter particles. This study suggests the possibility of having hot dark matter at the core of the neutron star and examines the possible signal of neutrons decaying in this way inside the neutron star right after its birth.

via astro-ph updates on arXiv.org https://ift.tt/4ETZo7s Aprire / Come

2022-06-24 05:36:57 arXiv:The FSU2H equation of state model, originally developed to describe cold neutron star matter with hyperonic cores, is extended to finite temperature. Results are presented for a wide range of temperatures and lepton fractions, which cover the conditions met in protoneutron star matter, neutron star mergers and supernova explosions. It is found that the temperature effects on the thermodynamical observables and the composition of the neutron star core are stronger when the hyperonic degrees of freedom are considered. An evaluation of the temperature and density dependence of the thermal index leads to the observation that the so-called $\Gamma$ law, widely used in neutron star merger simulations, is not appropriate to reproduce the true thermal effects, specially when hyperons start to be abundant in the neutron star core. To make finite temperature equations of state easily accessible, simple parameterizations of the thermal index for nucleonic and hyperonic $\beta$-stable neutrino-free matter are provided.

via astro-ph updates on arXiv.org https://ift.tt/PATKGFm Aprire / Come

2022-06-24 05:36:57 arXiv:Exoplanet atmospheres are inherently three-dimensional systems in which thermal/chemical variation and winds can strongly influence spectra. Recently, the ultra-hot Jupiter WASP-76 b has shown evidence for condensation and asymmetric Fe absorption with time. However, it is currently unclear whether these asymmetries are driven by chemical or thermal differences between the two limbs, as precise constraints on variation in these have remained elusive due to the challenges of modelling these dynamics in a Bayesian framework. To address this we develop a new model, HyDRA-2D, capable of simultaneously retrieving morning and evening terminators with day-night winds. We explore variations in Fe, temperature profile, winds and opacity deck with limb and orbital phase using VLT/ESPRESSO observations of WASP-76 b. We find Fe is more prominent on the evening for the last quarter of the transit, with $\log(X_\mathrm{Fe}) = {-4.03}^{+0.28}_{-0.31}$, but the morning shows a lower abundance with a wider uncertainty, $\log(X_\mathrm{Fe}) = {-4.59}^{+0.85}_{-1.0}$, driven by degeneracy with the opacity deck and the stronger evening signal. We constrain 0.1 mbar temperatures ranging from $2950^{+111}_{-156}$ K to $2615^{+266}_{-275}$ K, with a trend of higher temperatures for the more irradiated atmospheric regions. We also constrain a day-night wind speed of $9.8^{+1.2}_{-1.1}$ km/s for the last quarter, higher than $5.9^{+1.5}_{-1.1}$ km/s for the first, in line with general circulation models. We find our new spatially- and phase-resolved treatment is statistically favoured by 4.9$\sigma$ over traditional 1D-retrievals, and thus demonstrate the power of such modelling for robust constraints with current and future facilities.

via astro-ph updates on arXiv.org https://ift.tt/ujRkLic Aprire / Come

2022-06-24 05:36:56 arXiv:Ultra-light dark matter (ULDM) refers to a class of theories, including ultra-light axions, in which particles with mass $m_{\psi} < 10^{-20}\, \rm{eV}$ comprise a significant fraction of the dark matter. A galactic scale de Broglie wavelength distinguishes these theories from cold dark matter (CDM), suppressing the overall abundance of structure on sub-galactic scales, and producing wave-like interference phenomena in the density profiles of halos. With the aim of constraining the particle mass, we analyze the flux ratios in a sample of eleven quadruple-image strong gravitational lenses. We account for the suppression of the halo mass function and concentration-mass relation predicted by ULDM theories, and the wave-like fluctuations in the host halo density profile, calibrating the model for the wave interference against numerical simulations of galactic-scale halos. We show that the granular structure of halo density profiles, in particular, the amplitude of the fluctuations, significantly impacts image flux ratios, and therefore inferences on the particle mass derived from these data. We infer relative likelihoods of CDM to ULDM of 8:1, 7:1, 6:1, and 4:1 for particle masses $\log_{10}(m_\psi/\rm{eV})\in[-22.5,-22.25], [-22.25,-22.0],[-22.0,-21.75], [-21.75,-21.5]$, respectively. Repeating the analysis and omitting fluctuations associated with the wave interference effects, we obtain relative likelihoods of CDM to ULDM with a particle mass in the same ranges of 98:1, 48:1, 26:1 and 18:1, highlighting the significant perturbation to image flux ratios associated with the fluctuations. Nevertheless, our results disfavor the lightest particle masses with $m_{\psi} < 10^{-21.5}\,\rm{eV}$, adding to mounting pressure on ultra-light axions as a viable dark matter candidate.

via astro-ph updates on arXiv.org https://ift.tt/f1JFLwS Aprire / Come

2022-06-24 05:36:55 arXiv:We have identified 2XMM J125556.57+565846.4, at a distance of 600 pc, as a binary system consisting of a normal star and a probable dormant neutron star. Optical spectra exhibit a slightly evolved F-type single star, displaying periodic Doppler shifts with a 2.76-day Keplerian circular orbit, with no indication of light from a secondary component. Optical and UV photometry reveal ellipsoidal variations with half the orbital period, due to the tidal deformation of the F star. The mass of the unseen companion is constrained to the range $1.1$--$2.1\, M_{\odot}$ at $3\sigma$ confidence, with the median of the mass distribution at $1.4\, M_{\odot}$, the typical mass of known neutron stars. A main-sequence star cannot masquerade as the dark companion. The distribution of possible companion masses still allows for the possibility of a very massive white dwarf. The companion itself could also be a close pair consisting of a white dwarf and an M star, or two white dwarfs, although the binary evolution that would lead to such a close triple system is unlikely. Similar ambiguities regarding the certain identification of a dormant neutron star are bound to affect most future discoveries of this type of non-interacting system. If the system indeed contains a dormant neutron star, it will become, in the future, a bright X-ray source and might even host a millisecond pulsar.

via astro-ph updates on arXiv.org https://ift.tt/9hw2ByX Aprire / Come

2022-06-24 05:36:54 arXiv:Since its launch in 2008, the Fermi Large Area Telescope (LAT) allowed us to peek into the extremely energetic side of the Universe with unprecedented sensitivity and resolution. The tools available for analyzing Fermi-LAT data are the Fermitools and Fermipy, both of which can be scripted in Python and run via command lines in a terminal or in web-based interactive computing platforms. In this work, we are providing the community with easyFermi, an open-source user-friendly graphical interface for performing basic to intermediate analyses of Fermi-LAT data in the framework of Fermipy. With easyFermi, the user can quickly measure the $\gamma$-ray flux and photon index, build spectral energy distributions, light curves, test statistic maps, test for extended emission and even relocalize the coordinates of $\gamma$-ray sources. The tutorials for easyFermi are available on YouTube and GitHub, allowing the user to learn how to use Fermi-LAT data in about 10 min.

via astro-ph updates on arXiv.org https://ift.tt/U6jdV8a Aprire / Come

2022-06-24 05:36:53 arXiv:There is growing observational evidence for dwarf galaxies hosting active galactic nuclei (AGN), including hints of AGN-driven outflows in dwarfs. However, in the common theoretical model of galaxy formation, efficient supernova (SN) feedback is the tool of choice for regulating star formation in the low-mass regime. In this paper, we present a suite of high-resolution cosmological dwarf zoom-in simulations relaxing the assumption of strong SN feedback, with the goal to determine whether more moderate SN feedback in combination with an efficient AGN could be a suitable alternative. Importantly, we find that there are sufficient amounts of gas to power brief Eddington-limited accretion episodes in dwarfs. This leads to a variety of outcomes depending on the AGN accretion model: from no additional suppression to moderate regulation of star formation to catastrophic quenching. Efficient AGN can drive powerful outflows, depleting the gas reservoir of their hosts via ejective feedback and then maintaining a quiescent state through heating the circumgalactic medium. Moderate AGN outflows can be as efficient as the strong SN feedback commonly employed, leading to star formation regulation and HI gas masses in agreement with observations of field dwarfs. All efficient AGN set-ups are associated with overmassive black holes (BHs) compared to the (heavily extrapolated) observed BH mass - stellar mass scaling relations, with future direct observational constraints in this mass regime being crucially needed. Efficient AGN activity is mostly restricted to high redshifts, with hot, accelerated outflows and high X-ray luminosities being the clearest tell-tale signs for future observational campaigns.

via astro-ph updates on arXiv.org https://ift.tt/MiZy8BA Aprire / Come