Abstracts of Interest
Selected by:
Adnaan Thakur
Abstract: 2304.13022
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Title:The Calar Alto Legacy Integral Field Area Survey: extended and remastered data release
Download PDFAbstract: This paper describes the extended data release of the Calar Alto Legacy Integral Field Area (CALIFA) survey (eDR). It comprises science-grade quality data for 895 galaxies obtained with the PMAS/PPak instrument at the 3.5 m telescope at the Calar Alto Observatory along the last 12 years, using the V500 setup (3700-7500Å, 6Å/FWHM) and the CALIFA observing strategy. It includes galaxies of any morphological type, star-formation stage, a wide range of stellar masses ($\sim$10$^7$ 10$^{12}$ Msun ), at an average redshift of $\sim$0.015 (90\% within 0.005$<$z$<$0.05). Primarily selected based on the projected size and apparent magnitude, we demonstrate that it can be volume corrected resulting in a statistically limited but representative sample of the population of galaxies in the nearby Universe. All the data were homogeneous re-reduced, introducing a set of modifications to the previous reduction. The most relevant is the development and implementation of a new cube-reconstruction algorithm that provides with an (almost) seeing-limited spatial resolution (FWHM PSF $\sim$1.0").To illustrate the usability and quality of the data, we extracted two aperture spectra for each galaxy (central 1.5" and fully integrated), and analyze them using pyFIT3D. We obtain a set of observational and physical properties of both the stellar populations and the ionized gas, that have been compared for the two apertures, exploring their distributions as a function of the stellar masses and morphologies of the galaxies, comparing with recent results in the literature. DATA RELEASE: http://ifs.astroscu. this http URL
Abstract: 2304.12882
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Title:Discovery of extraordinary X-ray emission from magnetospheric interaction in the unique binary stellar system $ε$ Lupi
Download PDFAbstract: We report detailed X-ray observations of the unique binary system $\epsilon$ Lupi, the only known short-period binary consisting of two magnetic early-type stars. The components have comparably strong, but anti-aligned magnetic fields. The orbital and magnetic properties of the system imply that the magnetospheres overlap at all orbital phases, suggesting the possibility of variable inter-star magnetospheric interaction due to the non-negligible eccentricity of the orbit. To investigate this effect, we observed the X-ray emission from $\epsilon$ Lupi both near and away from periastron passage, using the Neutron Star Interior Composition Explorer mission (NICER) X-ray Telescope. We find that the system produces excess X-ray emission at the periastron phase, suggesting the presence of variable inter-star magnetospheric interaction. We also discover that the enhancement at periastron is confined to a very narrow orbital phase range ($\approx 5\%$ of the orbital period), but the X-ray properties close to periastron phase are similar to those observed away from periastron. From these observations, we infer that the underlying cause is magnetic reconnection heating the stellar wind plasma, rather than shocks produced by wind-wind collision. Finally, by comparing the behavior of $\epsilon$ Lupi with that observed for cooler magnetic binary systems, we propose that elevated X-ray flux at periastron phase is likely a general characteristic of interacting magnetospheres irrespective of the spectral types of the constituent stars.
Abstract: 2304.12800
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Title:Integral Field Spectroscopy of the Cometary Starburst Galaxy NGC 4861
Download PDFAbstract: Using the PMAS Integral Field Unit on the Calar Alto 3.5m telescope we observed the southern component (Markarian 59) of the `cometary' starburst galaxy NGC 4861. Mrk 59 is centred on a giant nebula and concentration of stars 1 kpc in diameter. Strong $\rm H\alpha$ emission points to a star-formation rate (SFR) at least 0.47 $\rm M_{\odot}yr^{-1}$. Mrk 59 has a very high [OIII]$\rm\lambda5007/H\beta$ ratio, reaching 7.35 in the central nebula, with a second peak at a star-forming hotspot further north. Fast outflows are not detected but nebular motion and galaxy rotation produce relative velocities up to 40 km $\rm s^{-1}$. Spectral analysis of different regions with `Fitting Analysis using Differential evolution Optimisation' (FADO) finds that the stars in the central and `spur' nebulae are very young, $\rm \leq125~Myr$ with a large $\rm <10~Myr$ contribution. Older stars ($\rm \sim 1~Gyr$), make up the northern disk component, while the other regions show mixtures of 1 Gyr age with very young stars. This and the high specific SFR $\rm\sim 3.5~Gyr^{-1}$ imply a bimodal star formation history, with Mrk 59 formed in ongoing starbursts fuelled by a huge gas inflow, turning the galaxy into an asymmetric `green pea' or blue compact dwarf. We map the HeII$\lambda4686$ emission, and identify a broad component from the central nebula, consistent with the emission of $\sim 300$ Wolf-Rayet stars. About a third of the HeII$\lambda$4686 flux is a narrow line emitted from a more extended area covering the central and spur nebulae, and may have a different origin.
Abstract: 2304.12752
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Title:The high polarisation of the X-rays from the Black Hole X-ray Binary 4U 1630-47 challenges standard thin accretion disc scenario
Download PDFAbstract: Large, energy-dependent X-ray polarisation is observed in 4U 1630-47, a black hole in an X-ray binary, in the high-soft emission state. In this state, X-ray emission is believed to be dominated by a thermal, geometrically thin, optically thick accretion disc. However, the observations with the Imaging X-ray Polarimetry Explorer (IXPE) reveal an unexpectedly high polarisation degree, rising from 6% at 2 keV to 10% at 8 keV, which cannot be reconciled with standard models of thin accretion discs. We argue that an accretion disc with an only partially ionised atmosphere flowing away from the disc at mildly relativistic velocities can explain the observations.
Abstract: 2304.12675
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Title:Search for correlations of high-energy neutrinos detected in IceCube with radio-bright AGN and gamma-ray emission from blazars
Download PDFAbstract: The IceCube Neutrino Observatory sends realtime neutrino alerts with high probability of being astrophysical in origin. We present a new method to correlate these events and possible candidate sources using $2,089$ blazars from the Fermi-LAT 4LAC-DR2 catalog and with $3,413$ AGNs from the Radio Fundamental Catalog. No statistically significant neutrino emission was found in any of the catalog searches. The result is compatible with a small fraction, $<1$%, of AGNs being neutrino emitters and prior evidence for neutrino emission presented by IceCube and other authors from sources such as TXS 0506+056 and PKS 1502+06. We also present cross-checks to other analyses that claim a significant correlation using similar data samples, and we find that adding more information on the neutrino events and more data overall makes the result compatible with background.
Abstract: 2304.12491
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Title:Spectral Energy Distributions for 258 Local Volume Galaxies
Download PDFAbstract: We present model spectral energy distribution (SED) fits to ultraviolet/optical/infrared observations for the 258 nearby galaxies in the Local Volume Legacy survey, a sample dominated by lower-luminosity dwarf irregular systems. The data for each galaxy include up to 26 spatially-integrated broadband and narrowband fluxes from the Galaxy Evolution Explorer, Spitzer Space Telescope, and Infrared Astronomical Satellite space-based platforms and from the Sloan Digital Sky Survey, Two Micron All Sky Survey, and other ground-based efforts. The CIGALE SED fitting package is employed using a delayed star formation history with an optional late burst or quenching episode to constrain 11 different free parameters that characterize the properties of each galaxy's stellar and dust emission, with the overriding constraint that the ultraviolet/optical emission absorbed by interstellar dust grains is emitted in equal energy portions at infrared wavelengths. The main results are: i) 94% of the SED fits yield reduced chi^2 values less than 3; ii) the modeled stellar masses agree with those derived from 3.6um-based measures with a scatter of 0.07 dex; iii) for a typical galaxy in the sample the SED-derived star formation rate averaged over the past 100 Myr is about 88% of the value derived from standard hybrid indicators on similar timescales; and iv) there is a statistically significant inverse relation between the stellar mass fraction appearing in the late burst and the total stellar mass. These results build upon prior SED modeling efforts in the local volume and lay the groundwork for future studies of more distant low-metallicity galaxies with JWST.
Abstract: 2304.12421
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Title:ALMACAL X: Constraints on molecular gas in the low-redshift circumgalactic medium
Download PDFAbstract: Despite its crucial role in galaxy evolution, the complex circumgalactic medium (CGM) remains underexplored. Although it is known to be multi-phase, the importance of the molecular gas phase to the total CGM mass budget is, to date, unconstrained. We present the first constraints on the molecular gas covering fraction in the CGM of low-redshift galaxies, using measurements of CO column densities along sightlines towards mm-bright background quasars with intervening galaxies. We do not detect molecular absorption against the background quasars. For the individual, low-redshift, 'normal' galaxy haloes probed here, we can therefore rule out the presence of an extremely molecular gas-rich CGM, as recently reported in high-redshift protoclusters and around luminous active galactic nuclei. We also set statistical limits on the volume filling factor of molecular material in the CGM as a whole, and as a function of radius. ISM-like molecular clouds of ~30 pc in radius with column densities of N(CO) >~ 10^16 cm^-2 have volume filling factors of less than 0.2 per cent. Large-scale smooth gas reservoirs are ruled out much more stringently. The development of this technique in the future will allow deeper constraining limits to be set on the importance (or unimportance) of molecular gas in the CGM.
Abstract: 2304.12394
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Title:Young but fading radio sources: searching for remnants among compact steep-spectrum radio sources
Download PDFAbstract: The incidence of young but fading radio sources provides important information on the life cycle of radio emission in radio-loud active galactic nuclei. Despite its importance for constraining the models of radio source evolution, there are no systematic studies of remnants in complete samples of young radio sources. We report results on the study of 18 compact steep-spectrum (CSS) radio sources, selected from the statistically complete B3-VLA CSS sample, characterized by a steep optically-thin spectrum (alpha > 1.0) and no core detection in earlier studies. Our deep multi-frequency Very Large Array (VLA), pc-scale Very Long Baseline Array (VLBA), and eMERLIN observations allowed us to locate the core component in 10 objects. In 3 CSS sources there is no clear evidence of present-time active regions, suggesting they are likely in a remnant phase. Among sources with core detection, we find 3 objects that have no clear active regions (hotspots) at the edges of the radio structure, suggesting that the radio emission may have just restarted. Our results support a power-law distribution of the source ages, although the poor statistics prevents us from setting solid constraints on the percentage of remnants and restarted sources in sub-populations of radio sources.
Abstract: 2304.12383
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Title:X-ray Spectroscopy of Interstellar Carbon: Evidence for Scattering by Carbon-Bearing Material in the Spectrum of 1ES 1553+113
Download PDFAbstract: Molecules and particles make up $\sim 40 - 70\%$ of carbon in the interstellar medium, yet the exact chemical structure of these constituents remains unknown. We present carbon K-shell absorption spectroscopy of the Galactic Interstellar Medium obtained with the Low Energy Transmission Grating Spectrometer on the {\it Chandra} Observatory, that directly addresses this question. We probe several lines of sight, using bright AGN as backlighters. We make our measurements differentially with respect to the bright source Mrk 421, in order to take the significant carbon K absorption in the instrument into account. In the spectrum of the blazar 1ES 1553+113 we find evidence for a novel feature: strong extinction on the low-energy side of the neutral C $1s-2p$ resonance, which is indicative of scattering by graphite particles. We find evidence for characteristic particle radii of order $0.1-0.15$ $\mu$m. If this explanation for the feature is correct, limits on the mass of the available carbon along the line of sight may imply that the grains are partially aligned, and the X-rays from the source may have intrinsic polarization.
Abstract: 2304.12368
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Title:Record-breaking polarization from the interacting superluminous supernova 2017hcc
Download PDFAbstract: We present multiepoch spectropolarimetry of the superluminous interacting Type IIn supernova SN2017hcc, covering 16 to 391 days after explosion. In our first epoch we measure continuum polarization as high as 6%, making SN 2017hcc the most intrinsically polarized SN ever reported. During the first 29 days of coverage, when the polarization is strongest, the continuum polarization has a wavelength dependence that rises toward blue wavelengths, and becomes wavelength independent by day 45. The polarization strength drops rapidly during the first month, even as the SN flux is still climbing to peak brightness. Nonetheless, record-high polarization is maintained until day 68, at which point the source polarization declines to 1.9%, comparable to peak levels in previous well-studied SNe IIn. Thereafter the SN continues in polarization decline, while exhibiting only minor changes in position angle on the sky. The blue slope of the polarized continuum during the first month, accompanied by short-lived polarized flux for Balmer emission, suggests that an aspherical distribution of dust grains in pre-shock circumstellar material (CSM) is echoing the SN IIn spectrum and strongly influencing the polarization, while the subsequent decline during the wavelength-independent phase appears broadly consistent with electron scattering near the SN/CSM interface. The persistence of the polarization position angle between these two phases suggests that the pre-existing CSM responsible for the dust scattering at early times is part of the same geometric structure as the electron-scattering region that dominates the polarization at later times. SN2017hcc appears to be yet another, but much more extreme, case of aspherical yet well-ordered CSM in Type IIn SNe, possibly resulting from pre-SN mass loss shaped by a binary progenitor system.
Abstract: 2304.12358
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Title:Evidence for two distinct populations of kilonova-associated Gamma Ray Bursts
Download PDFAbstract: Identification of Gamma Ray Burst (GRB) progenitors based on the duration of their prompt emission ($T_{90}$) has faced several roadblocks recently. Long-duration GRBs (with $T_{90} > 2s$) have traditionally been thought to be originating from the collapse of massive stars, and the short-duration ones (with $T_{90} < 2s$) from compact binary mergers. However, recent observations of a long GRB associated with a kilonova (KN) and a short GRB with supernova (SN) association demand a more detailed classification of the GRB population. In this {\it Letter}, we focus on GRBs associated with KNe, believed to be originating from mergers of binaries involving neutron stars (NS). We make use of the GRB prompt emission light curves of {\it Swift}-BAT 2022 GRB catalog and employ machine learning algorithms to study the classification of GRB progenitors. Our analysis reveals that there are five distinct clusters of GRBs, of which the KN-associated GRBs are located in two separate clusters indicating they may have been produced by different progenitors. We argue that these clusters may be due to subclasses of binary neutron star (BNS) and/or neutron star--black hole (NS-BH) mergers. We also discuss the implications of these findings for future gravitational-wave (GW) observations and how those observations may help in understanding these clusters better.
Abstract: 2304.12357
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Title:Line emission from filaments in molecular clouds
Download PDFAbstract: Filamentary structures are often identified in column density maps of molecular clouds, and appear to be important for both low- and high-mass star formation. Theoretically, these structures are expected to form in regions where the supersonic cloud-scale turbulent velocity field converges. While this model of filament formation successfully reproduces several of their properties derived from column densities, it is unclear whether it can also reproduce their kinematic features. We use a combination of hydrodynamical, chemical and radiative transfer modelling to predict the emission properties of these dynamically-forming filaments in the $^{13}$CO, HCN and N$_2$H$^+$ $J=1-0$ rotational lines. The results are largely in agreement with observations; in particular, line widths are typically subsonic to transonic, even for filaments which have formed from highly supersonic inflows. If the observed filaments are formed dynamically, as our results suggest, no equilibrium analysis is possible, and simulations which presuppose the existence of a filament are likely to produce unrealistic results.
Abstract: 2304.12333
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Title:Radio Emission from the First Quasars
Download PDFAbstract: Over 200 quasars have now been discovered at $z >$ 6, including nine at $z >$ 7. They are thought to form from the collapse of supermassive primordial stars to 10$^4$ - 10$^5$ M$_{\odot}$ black holes at $z \sim$ 20 - 25, which then rapidly grow in the low-shear environments of rare, massive halos fed by strong accretion flows. Sensitive new radio telescopes such as the Next-Generation Very Large Array (ngVLA) and the Square Kilometer Array (SKA) could probe the growth of these objects at much earliest stages than is now possible. Here, we estimate radio flux from the first quasars at $z \sim$ 6 - 15 at 1 - 10 GHz. We find that a quasar with properties similar to that of ULAS J1120+0641, a 2.1 $\times$ 10$^9$ M$_{\odot}$ black hole at $z =$ 7.1, could be detected at up to $z \sim$ 16 by the SKA and at $z \sim$ 14 by the ngVLA. The advent of these new observatories, together with the James Webb Space Telescope (JWST), Euclid, and the Roman Space Telescope (RST), will inaugurate the era of $z \lesssim$ 15 quasar astronomy in the coming decade.
Abstract: 2304.11992
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Title:Terzina on board NUSES: a pathfinder for EAS Cherenkov Light Detection from space
Download PDFAbstract: In this paper we introduce the Terzina telescope as a part of the NUSES space mission. This telescope aims to detect Ultra High Energy Cosmic Rays (UHECRs) through the Cherenkov light emission from the extensive air showers (EAS) that they create in the Earth's atmosphere. The Cherenkov photons are aligned along the shower axis inside about $\sim 0.2-1^{\circ}$, so that they become detectable by Terzina when it points towards the Earth's limb. A sun-synchronous orbit will allow the telescope to observe only the night side of the Earth's atmosphere. In this contribution, we focus on the description of the telescope detection goals, geometry, optical design and its photon detection camera composed of Silicon Photo-Multipliers (SiPMs). Moreover, we describe the full Monte Carlo simulation chain developed to estimate Terzina's performance for UHECR detection. The estimate of the radiation damage and light background rates, the readout electronics and trigger logic are briefly described. Terzina will be able to study the potential for future physics missions devoted to UHECR detection and to UHE neutrino astronomy. It is a pathfinder for missions like POEMMA or future constellations of similar satellites to NUSES.
Abstract: 2304.11937
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Title:Timing analysis of Swift J0243.6+6124 with NICER and Fermi/GBM during the decay phase of the 2017-2018 outburst
Download PDFAbstract: We present a timing and noise analysis of the Be/X-ray binary system Swift J0243.6+6124 during its 2017-2018 super-Eddington outburst using NICER/XTI observations. For the initial segments of the data that overlap with the Fermi/GBM pulse frequency history, we apply a synthetic pulse timing analysis to enrich the spin frequency history of the source. In addition, we employ phase-coherent timing analysis for NICER/XTI observations that extends beyond the Fermi/GBM frequency history. We show that the pulse profiles switch from double-peaked to single-peaked when the X-ray luminosity drops below $\sim$$7\times 10^{36}$ erg s$^{-1}$. We suggest that this transitional luminosity is associated with the transition from a pencil beam pattern to a hybrid beam pattern when the Coulomb interactions become ineffective to decelerate the accretion flow, which implies a dipolar magnetic field strength of $\sim$$5\times 10^{12}$ G. We also obtained the power density spectra (PDS) of the spin frequency derivative fluctuations. The red noise component of the PDS is found to be steeper ($\omega^{-3.36}$) than the other transient accreting sources. We find significantly high noise strength estimates above the super-Eddington luminosity levels, which may arise from the torque fluctuations due to interactions with the quadrupole fields at such levels.
Abstract: 2304.11784
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Title:MeerKAT discovery of a double radio relic and odd radio circle
Download PDFAbstract: We present the serendipitous discovery of a large double radio relic associated with the merging galaxy cluster PSZ2 G277.93+12.34 and a new odd radio circle, ORC J1027-4422, both found in deep MeerKAT 1.3 GHz wide-band data. The angular separation of the two arc-shaped cluster relics is 16 arcmin or 2.6 Mpc for a cluster redshift of z = 0.158. The thin southern relic, which shows a number of ridges/shocks including one possibly moving inwards, has a linear extent of 1.64 Mpc. In contrast, the northern relic is about twice as wide, twice as bright, but only has a largest linear size of 0.66 Mpc. Complementary SRG/eROSITA X-ray images reveal extended emission from hot intracluster gas between the two relics and around the narrow-angle tail (NAT) radio galaxy PMN J1033-4335 (z = 0.153) located just east of the northern relic. No radio halo associated with the PSZ2 cluster is detected. The radio morphologies of the NAT galaxy and the northern relic, which are also detected with the Australian Square Kilometer Array Pathfinder at 887.5 MHz, suggest both are moving in the same outward direction. The discovery of ORC J1027-4422 in a different part of the MeerKAT image makes it the 4th known single ORC. It has a diameter of 90" corresponding to 400 kpc at a tentative redshift of z = 0.3 and remains undetected in X-ray emission. We discuss similarities between galaxy and cluster mergers as the formation mechanisms for ORCs and radio relics, respectively.
Abstract: 2304.11360
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Title:Multi-messenger signals of heavy axionlike particles in core-collapse supernovae: two-dimensional simulations
Download PDFAbstract: Core-collapse supernovae are a useful laboratory to probe the nature of exotic particles. If axionlike particles (ALPs) are produced in supernovae, they can affect the transfer of energy and leave traces in observational signatures. In this work, we develop two-dimensional supernova models including the effects of the production and the absorption of ALPs that couple with photons. It is found that the additional heating induced by ALPs can enhance the explosion energy E_exp; for moderate ALP-photon coupling, we find explosion energies ~0.6*10^51 erg compared to our reference model without ALPs of ~0.4*10^51 erg. Our findings also indicate that when the coupling constant is sufficiently high, the neutrino luminosities and mean energies are decreased because of the additional cooling of the proto-neutron star. The gravitational wave strain is also reduced because the mass accretion on the proto-neutron star is suppressed. Although the ALP-photon coupling can foster explodability, including enhancing the explosion energy closer to recent observations, more long-term simulations in spatially three-dimension are needed to draw robust conclusions.
Abstract: 2304.11225
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Title:First Detection of the Powerful Gamma Ray Burst GRB221009A by the THEMIS ESA and SST particle detectors on October 9, 2022
Download PDFAbstract: We present the first results study of the effects of the powerful Gamma Ray Burst GRB 221009A that occurred on October 9, 2022, and was serendipitously recorded by electron and proton detectors aboard the four spacecraft of the NASA THEMIS mission. Long-duration gamma-ray bursts (GRBs) are powerful cosmic explosions, signaling the death of massive stars, and, among them, GRB 221009A is so far the brightest burst ever observed due to its enormous energy ($E_{\gamma iso}\sim10^{55}$ erg) and proximity (the redshift is $z\sim 0.1505$). The THEMIS mission launched in 2008 was designed to study the plasma processes in the Earth's magnetosphere and the solar wind. The particle flux measurements from the two inner magnetosphere THEMIS probes THA and THE and ARTEMIS spacecraft THB and THC orbiting the Moon captured the dynamics of GRB 221009A with a high-time resolution of more than 20 measurements per second. This allowed us to resolve the fine structure of the gamma-ray burst and determine the temporal scales of the two main bursts spiky structure complementing the results from gamma-ray space telescopes and detectors.
Abstract: 2304.11222
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Title:Shimmering gravitons in the gamma-ray sky
Download PDFAbstract: What is the highest energy at which gravitons can be observed? We address this question by studying graviton-to-photon conversion - the inverse-Gertsenshtein effect - in the magnetic field of the Milky Way. We find that above $\sim 1~\mbox{PeV}$ the effective photon mass grows large enough to quench the conversion rate. The induced photon flux is comparable to the sensitivity of LHAASO to a diffuse $\gamma$-ray background, but only for graviton abundances of order $\Omega_{\text{gw}} h^2_0 \sim 1$. In the future, owing to a better understanding of $\gamma$-ray backgrounds, larger effective areas and longer observation times, sub-PeV shimmering gravitons with a realistic abundance of $\Omega_{\text{gw}} h^2_0 \sim 0.01$ could be detected. We show that this is achieved in a cosmologically-motivated scenario of post-recombination superheavy dark matter decay. Therefore, the sub-PeV range might be the ultimate energy frontier at which gravitons can be observed.
Abstract: 2304.11216
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Title:Statistical study of a large and cleaned sample of ultraluminous and hyperluminous X-ray sources
Download PDFAbstract: Ultra-/hyperluminous X-ray sources (ULX/HLX) could be interesting laboratories to further improve our understanding of the supermassive black hole growth through super-Eddington accretion episodes and successive mergers of lighter holes. ULXs are thought to be powered by super-Eddington accretion onto stellar-mass compact objects, while HLXs may be accreting intermediate mass black holes (IMBH). However, a significant portion of the sample of ULX/HLX candidates derived from catalogue searches are background AGN. Here we build ULX and HLX samples from recent XMM-Newton, Swift-XRT and Chandra catalogues and the GLADE catalogue of galaxies. We aim to characterise the frequency, environment, hardness and variability of ULXs and HLXs to better assess their differences and understand their populations. After a thorough classification of these X-ray sources, we remove 42% of $S/N>3$ sources shown to be contaminants, to obtain the cleanest sample of ULX/HLX to date. From a sample of 1342 ULXs and 191 HLXs, we study the occupation fraction, hardness, variability, radial distribution and preferred environment of the sources. We build their Malmquist-corrected X-ray luminosity functions (XLF) and compare them with previous studies. We statistically compare ULXs and HLXs and assess the differences in their nature. The interpretation of HLXs as IMBHs is investigated. A significant break is seen in the XLF at $\sim 10^{40}$ erg/s. Our ULX sample, having $\leq 2$% of contaminants, confirms that ULXs are located preferentially in spiral galaxies and galaxies with higher star-formation rates. Unlike ULXs, HLXs seem to reside equally in spiral and lenticular/elliptical galaxies. 35% of the HLX candidates have an optical counterpart, and we estimate the mass of 120 of them in the range of $2000-10^5 M_\odot$. Most HLXs are consistent with an accreting massive black hole in a dwarf galaxy satellite.
Abstract: 2304.11197
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Title:Improving the Composition of Ultra High Energy Cosmic Rays with Ground Detector Data
Download PDFAbstract: We show that the maximum shower depth ($X_{\rm max}$) distributions of Ultra-High Energy Cosmic Rays (UHECRs), as measured by fluorescence telescopes, can be augmented by building a mapping to observables collected by surface detectors. Using the publicly available data on "golden hybrid'' events from the Pierre Auger Observatory we demonstrate significant correlations between $X_{\rm max}$ and timing information from ground Cherenkov detectors. Using such a mapping we show how to incorporate a subset of ground data into the inference of the $X_{\rm max}$ distribution, where the size of this subset depends on the strength of the correlation found. With a simple linear fit model, we are able to effectively incorporate $\sim13\%$ of all ground data statistics. Finally, we use this augmented dataset to infer the composition of UHECRs and discriminate between hadronic models used in air shower development simulations, and show the results improve significantly due to the effectively larger statistics available.
Abstract: 2304.11188
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Title:Key Science Goals for the Next-Generation Event Horizon Telescope
Download PDFAbstract: The Event Horizon Telescope (EHT) has led to the first images of a supermassive black hole, revealing the central compact objects in the elliptical galaxy M87 and the Milky Way. Proposed upgrades to this array through the next-generation EHT (ngEHT) program would sharply improve the angular resolution, dynamic range, and temporal coverage of the existing EHT observations. These improvements will uniquely enable a wealth of transformative new discoveries related to black hole science, extending from event-horizon-scale studies of strong gravity to studies of explosive transients to the cosmological growth and influence of supermassive black holes. Here, we present the key science goals for the ngEHT and their associated instrument requirements, both of which have been formulated through a multi-year international effort involving hundreds of scientists worldwide.
Abstract: 2304.10934
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Title:A Cross-correlation Study between IceCube Neutrino Events and the Fermi Unresolved Gamma-ray Sky
Download PDFAbstract: With the coincident detections of electromagnetic radiation together with gravitational waves (GW170817) or neutrinos (TXS 0506+056), the new era of multimessenger astrophysics has begun. Of particular interest are the searches for correlation between the high-energy astrophysical neutrinos detected by the IceCube Observatory and gamma-ray photons detected by the Fermi Large Area Telescope (LAT). So far, only sources detected by the LAT have been considered in correlation with IceCube neutrinos, neglecting any emission from sources too faint to be resolved individually. Here, we present the first cross-correlation analysis considering the unresolved gamma-ray background (UGRB) and IceCube events. We perform a thorough sensitivity study and, given the lack of identified correlation, we place upper limits on the fraction of the observed neutrinos that would be produced in proton-proton (p-p) or proton-gamma (p-gamma) interactions from the population of sources contributing to the UGRB emission and dominating its spatial anisotropy (aka blazars). Our analysis suggests that, under the assumption that there is no intrinsic cutoff and/or hardening of the spectrum above Fermi-LAT energies, and that all gamma-rays from the unresolved blazars dominating the UGRB fluctuation field are produced by neutral pions from p-p (p-gamma) interactions, up to 60% (30%) of such population may contribute to the total neutrino events observed by IceCube. This translates into a O(1%) maximum contribution to the astrophysical high-energy neutrino flux observed by IceCube at 100 TeV.
Abstract: 2304.10871
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Title:Neutron star phase transition as the origin for the fast radio bursts and soft gamma-ray repeaters of SGR J1935+2154
Download PDFAbstract: Magnetars are believed as neutron stars (NSs) with strong magnetic fields. X-ray flares and fast radio bursts (FRBs) have been observed from the magnetar (soft gamma-ray repeater, SGR J1935+2154). We propose that the phase transition of the NS can power the FRBs and SGRs.Based on the equation of state provided by the MIT bag model and the mean field approximation, we solve the Tolman-Oppenheimer-Volkoff equations to get the NS structure. With spin-down of the NS, the hadronic shell gradually transfers to the quark shell.The gravitational potential energy released by one time of the phase transition can be achieved. The released energy, time interval between two successive phase transitions, and glitch are all consistent with the observations of the FRBs and the X-ray flares from SGR J1935+2154. We conclude that the phase transition of an NS is a plausible mechanism to power the SGRs as well as the repeating FRBs.
Abstract: 2304.10815
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Title:The spin-down accretion regime of Galactic ultra-luminous X-ray pulsar Swift J0243.6+6124
Download PDFAbstract: The relative high fluxes of the Galactic ultra-luminous X-ray pulsar Swift J0243 allow a detailed study of its spin-down regime in quiescence state, for a first time. After the 2017 giant outburst, its spin frequencies show a linear decreasing trend with some variations due to minor outbursts. The linear spin-down rate is $\sim-1.9\times10^{-12}$ Hz/s during the period of lowest luminosity, from which one can infer a dipole field $\sim1.75\times10^{13}$ G. The $\dot{\nu}-L$ relation during the spin-down regime is complex, and the $\dot{\nu}$ is close to 0 when the luminosity reaches both the high end ($L_{38}\sim0.3$) and the lowest value ($L_{38}\sim0.03$). The luminosity of zero-torque is different for the giant outburst and other minor outbursts. It is likely due to different accretion flows for different types of outburst, as evidenced by the differences of the spectra and pulse profiles at a similar luminosity for different types of outburst (giant or not). The pulse profile changes from double peaks in the spin-up state to a single broad peak in the low spin-down regime, indicating the emission beam/region is larger in the low spin-down regime. These results show that accretion is still ongoing in the low spin-down regime for which the neutron star is supposed to be in a propeller state.
Abstract: 2304.10715
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Full Text: [ PostScript, PDF]
Title:Flares from merged magnetars: their prospects as a new population of gamma-ray counterparts of binary neutron star mergers
Download PDFAbstract: Long-lived massive magnetars are expected to be remnants of some binary neutron star (BNS) mergers. In this paper, we argue that the magnetic powered flaring activities of these merged magnetars would occur dominantly in their early millisecond-period-spin phase, which is in the timescale of days. Such flares endure significant absorption by the ejecta from the BNS collision, and their detectable energy range is from 0.1-10 MeV, in a time-lag of $\sim$ days after the merger events indicated by the gravitational wave chirps. We estimate the rate of such flares in different energy ranges, and find that there could have been ~0.1-10 cases detected by Fermi/GBM. A careful search for $\sim10$ milliseconds spin period modulation in weak short gamma-ray bursts (GRBs) may identify them from the archival data. Future MeV detectors can detect them at a rate from a few to tens per year. The recent report on the Quasi-Period-Oscillation found in two BASTE GRBs should not be considered as cases of such flares, for they were detection in a lower energy range and with a much shorter period spin modulation.
Abstract: 2304.10688
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Full Text: [ PostScript, PDF]
Title:Effects of large-scale magnetic fields on the observed composition of ultra high-energy cosmic rays
Download PDFAbstract: Ultra high-energy (UHE) cosmic rays (CRs) from distant sources interact with intergalactic radiation fields, leading to their spallation and attenuation. They are also deflected in intergalactic magnetic fields (IGMFs), particularly those associated with Mpc-scale structures. These deflections extend the propagation times of CR particles, forming a magnetic horizon for each CR species. The cumulative cooling and interactions of a CR ensemble also modifies their spectral shape and composition observed on Earth. We construct a transport formulation to calculate the observed UHE CR spectral composition for 4 classes of source population. The effects on CR propagation brought about by IGMFs are modeled as scattering processes during transport, by centers associated with cosmic filaments. Our calculations demonstrate that IGMFs can have a marked effect on observed UHE CRs, and that source population models are degenerate with IGMF properties. Interpretation of observations, including the endorsement or rejection of any particular source classes, thus needs careful consideration of the structural properties and evolution of IGMFs. Future observations providing tighter constraints on IGMF properties will significantly improve confidence in assessing UHE CR sources and their intrinsic CR production properties.
Abstract: 2304.10534
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Full Text: [ PostScript, PDF]
Title:TONE: A CHIME/FRB Outrigger Pathfinder for localizations of Fast Radio Bursts using Very Long Baseline Interferometry
Download PDFAbstract: The sensitivity and field of view of the Canadian Hydrogen Intensity Mapping Experiment (CHIME) has enabled its fast radio burst (FRB) backend to detect thousands of FRBs. However, the low angular resolution of CHIME prevents it from localizing most FRBs to their host galaxies. Very long baseline interferometry (VLBI) can readily provide the subarcsecond resolution needed to localize many FRBs to their hosts. Thus we developed TONE: an interferometric array of eight $6~\mathrm{m}$ dishes to serve as a pathfinder for the CHIME/FRB Outriggers project, which will use wide field of view cylinders to determine the sky positions for a large sample of FRBs, revealing their positions within their host galaxies to subarcsecond precision. In the meantime, TONE's $\sim3333~\mathrm{km}$ baseline with CHIME proves to be an excellent testbed for the development and characterization of single-pulse VLBI techniques at the time of discovery. This work describes the TONE instrument, its sensitivity, and its astrometric precision in single-pulse VLBI. We believe that our astrometric errors are dominated by uncertainties in the clock measurements which build up between successive Crab pulsar calibrations which happen every $\approx 24~\mathrm{h}$; the wider fields of view and higher sensitivity of the Outriggers will provide opportunities for higher-cadence calibration. At present, CHIME-TONE localizations of the Crab pulsar yield systematic localization errors of ${0.1}-{0.2}~\mathrm{arcsec}$ - comparable to the resolution afforded by state-of-the-art optical instruments ($\sim 0.05 ~\mathrm{arcsec}$).
Abstract: 2304.10471
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Full Text: [ PostScript, PDF]
Title:WISDOM Project -- XV. Giant Molecular Clouds in the Central Region of the Barred Spiral Galaxy NGC 5806
Download PDFAbstract: We present high spatial resolution ($\approx24$ pc) Atacama Large Millimeter/sub-millimeter Array $^{12}$CO(2-1) observations of the central region of the nearby barred spiral galaxy NGC 5806. NGC 5806 has a highly structured molecular gas distribution with a clear nucleus, a nuclear ring and offset dust lanes. We identify $170$ spatially- and spectrally-resolved giant molecular clouds (GMCs). These clouds have comparable sizes ($R_{\mathrm{c}}$) and larger gas masses, observed linewidths ($\sigma_{\mathrm{obs,los}}$) and gas mass surface densities than those of clouds in the Milky Way disc. The size -- linewidth relation of the clouds is one of the steepest reported so far ($\sigma_{\mathrm{obs,los}}\propto R_{\mathrm{c}}^{1.20}$), the clouds are on average only marginally bound (with a mean virial parameter $\langle\alpha_{\mathrm{vir}}\rangle\approx2$), and high velocity dispersions are observed in the nuclear ring. These behaviours are likely due to bar-driven gas shocks and inflows along the offset dust lanes, and we infer an inflow velocity of $\approx120$ kms$^{-1}$ and a total molecular gas mass inflow rate of $\approx5$ M$_\odot$ yr$^{-1}$ into the nuclear ring. The observed internal velocity gradients of the clouds are consistent with internal turbulence. The number of clouds in the nuclear ring decreases with azimuthal angle downstream from the dust lanes without clear variation of cloud properties. This is likely due to the estimated short lifetime of the clouds ($\approx6$ Myr), which appears to be mainly regulated by cloud-cloud collision and/or shear processes. Overall, it thus seems that the presence of the large-scale bar and gas inflows to the centre of NGC 5806 affect cloud properties.
Abstract: 2304.10416
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Full Text: [ PostScript, PDF]
Title:A Superluminous Supernova Lightened by Collisions with Pulsational Pair-instability Shells
Download PDFAbstract: Superluminous supernovae are among the most energetic stellar explosions in the Universe, but their energy sources remain an open question. Here we present long-term observations of one of the closest examples of the hydrogen-poor subclass (SLSNe-I), SN~2017egm, revealing the most complicated known luminosity evolution of SLSNe-I. Three distinct post-peak bumps were recorded in its light curve collected at about $100$--350\,days after maximum brightness, challenging current popular power models such as magnetar, fallback accretion, and interaction between ejecta and a circumstellar shell. However, the complex light curve can be well modelled by successive interactions with multiple circumstellar shells with a total mass of about $6.8$--7.7\,M$_\odot$. In this scenario, large energy deposition from interaction-induced reverse shocks results in ionization of neutral oxygen in the supernova ejecta and hence a much lower nebular-phase line ratio of [O\,\textsc{i}] $\lambda6300$/([Ca\,\textsc{ii}] + [O\,\textsc{ii}]) $\lambda7300$ ($\sim 0.2$) compared with that derived for other superluminous and normal stripped-envelope SNe. The pre-existing multiple shells indicate that the progenitor of SN~2017egm experienced pulsational mass ejections triggered by pair instability within 2 years before explosion, in robust agreement with theoretical predictions for a pre-pulsation helium-core mass of 48--51\,M$_{\odot}$.
Abstract: 2304.10377
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Full Text: [ PostScript, PDF]
Title:Constraining the Molecular Gas Content of Fast Radio Burst (FRB) Host Galaxies
Download PDFAbstract: We used Bands 6 and 7 of the Atacama Large Millimeter/submillimeter Array (ALMA) in Cycles 7 and 8 to search for $\mathrm{CO}\,(3-2)$ emission from a sample of five fast radio burst (FRB) host galaxies discovered by the Commensal Real-time ASKAP Fast Transients (CRAFT) survey and the Fast and Fortunate for FRB Follow-up (F$^4$) team. These galaxies have redshifts $z \approx 0.16-0.48$, masses log$(M_{\rm star}/M_{\odot})\approx 9.30-10.4$ characteristic of field galaxies, and emission lines indicative of ongoing star formation. We detected three of the five galaxies with luminosities $L'(3-2)\approx0.2-4\times10^8\,\rm K\,km \, s^{-1}\,pc^2$ and set upper limits for the other two. Adopting standard metallicity-dependent CO-to-H$_2$ conversion factors, we estimate molecular gas masses $M_{\rm gas}\approx 0.2-3\times 10^9 \, M_{\odot}$. As a population, FRB host galaxies track the main $M_{\rm star}-M_{\rm gas}$ locus of star-forming galaxies in the present-day universe, with gas fractions of $\mu_{\rm gas}\approx0.1$ and gas depletion times $t_{\rm dep} \gtrapprox 1\,$Gyr. We employ the Kaplan-Meier estimator to compare the redshift-corrected $\mu_{\rm gas}$ and $t_{\rm dep}$ for all known FRB hosts with measurements or upper limits with those from the xCOLD GASS survey and find statistically different gas fractions. The difference is not statistically significant when we consider only the five hosts studied here with consistently determined properties, suggesting more FRB hosts with measured molecular gas masses are needed to robustly study the population. Lastly, we present a multi-wavelength analysis of one host (HG20180924B) combining high-spatial resolution imaging and integral field spectroscopy to demonstrate that future high-resolution observations will allow us to study the host galaxy environments local to the FRBs.
Abstract: 2304.10233
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Full Text: [ PostScript, PDF]
Title:Massive black holes in galactic nuclei: Observations
Download PDFAbstract: Since a black hole does not emit light from its interior, nor does it have a surface on which light from nearby sources can be reflected, observational study of black hole physics requires observing the gravitational impact of the black hole on its surroundings. A massive black hole leaves a dynamical imprint on stars and gas close by. Gas in the immediate vicinity of an accreting massive black hole can, due to the presence of the black hole, shine so brightly that it outshines the light of the billions of stars in its host galaxy and be detected across the Universe. By observing the emission from stars and gas and determining their kinematics scientists can extract vital information not only on the fundamental properties of the black holes themselves but also the impact they have on their surroundings. As it turns out, supermassive black holes appear to play a vital role in shaping the Universe as we know it, as they can profoundly impact the star formation history in galaxies. As a consequence, these black holes indirectly impact the cosmic build up of chemical elements heavier than Helium and thus affect when and where life can form. For these reasons alone, observations of massive black holes constitute a very active research area of modern astrophysics.
In this chapter we aim to provide a general overview -- fit for a non-expert -- of what scientists have learned, and hope to learn, from analyzing observations of massive black holes and the material around them.
Abstract: 2304.10188
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Full Text: [ PostScript, PDF]
Title:Hard TeV Gamma-Ray Afterglows of Nearby GRB 190829A as a Tentative Signature of Ultra-High-Energy Cosmic Rays Accelerated in Gamma-Ray Burst Jets
Download PDFAbstract: The observed hard TeV gamma-ray spectrum of the nearby gamma-ray burst (GRB) 190829A may challenge the conventional leptonic GRB afterglow model. It has been proposed that an ultra-high-energy (UHE; $\varepsilon^{'}_{\rm p}\sim 10^{20}$ eV) proton population can be pre-accelerated by internal shocks in GRB jets. We study possible signatures of the UHE protons embedded in the TeV afterglows when they escape the afterglow fireball. We show that the leptonic model can represent the observed multiwavelength lightcurves and spectral energy distributions of GRB 190829A by considering the uncertainties of the model parameters. Attributing the TeV gamma-ray afterglows to the emission of both the electron self-Compton scattering process and the UHE proton synchrotron radiations in the afterglow fireball, we obtain tentative upper limits of $\log_{10} \varepsilon_{\rm p}^{\prime}/{\rm eV}\sim 20.46$ and $\log_{10}E_{\rm p, total}/{\rm erg}\leq 50.75$, where $E_{\rm p, total}$ is the total energy of the proton population. The synchrotron radiations of the UHE protons should dominate the early TeV gamma-ray afterglows, implying that early observations are critical for revealing the UHE proton population.
Abstract: 2303.12849
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Full Text: [ PostScript, PDF]
Title:A Sensitive Search for Supernova Emission Associated with the Extremely Energetic and Nearby GRB 221009A
Download PDFAbstract: We report observations of the optical counterpart of the long gamma-ray burst (LGRB) GRB 221009A. Due to the extreme rarity of being both nearby ($z = 0.151$) and highly energetic ($E_{\gamma,\mathrm{iso}} \geq 10^{54}$ erg), GRB 221009A offers a unique opportunity to probe the connection between massive star core collapse and relativistic jet formation. Adopting a phenomenological power-law model for the afterglow and host galaxy estimates from high-resolution Hubble Space Telescope imaging, we use Bayesian model comparison techniques to determine the likelihood of an associated SN contributing excess flux to the optical light curve. Though not conclusive, we find moderate evidence ($K_{\rm{Bayes}}=10^{1.2}$) for the presence of an additional component arising from an associated supernova, SN 2022xiw, and find that it must be substantially fainter than SN 1998bw. Given the large and uncertain line-of-sight extinction, we attempt to constrain the supernova parameters ($M_{\mathrm{Ni}}$, $M_{\mathrm{ej}}$, and $E_{\mathrm{KE}}$) under several different assumptions with respect to the host galaxy's extinction. We find properties that are broadly consistent with previous GRB-associated SNe: $M_{\rm{Ni}}=0.05$ - $0.25$ ${M_\odot}$, $M_{\rm{ej}}=3.5$ - $11.1$ ${M_\odot}$, and $E_{\rm{KE}} = (1.6$ - $5.2) \times 10^{52} \rm{erg}$. We note that these properties are weakly constrained due to the faintness of the supernova with respect to the afterglow and host emission, but we do find a robust upper limit on the Nickel mass of $M_{\rm{Ni}}<0.36$ $\rm{M_\odot}$. Given the tremendous range in isotropic gamma-ray energy release exhibited by GRBs (7 orders of magnitude), the SN emission appears to be decoupled from the central engine in these systems.
Abstract: 2303.00782
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Full Text: [ PostScript, PDF]
Title:Discovery of Extended Fe Ka Complex X-ray Emission in NGC 5728
Download PDFAbstract: We present Chandra ACIS imaging spectroscopy results for the extended (1.5$''$-8$''$) hard X-ray emission of the Compton thick (CT) Seyfert NGC 5728. We find spectrally and spatially-resolved features in the Fe K$\alpha$ complex (5.5-7.2 keV), redward and blueward of the neutral 6.4 keV line in the extended bicone. The [red, blue] features have [6.5$\sigma$, 5.3$\sigma$] significance, with an equivalent width = [1.76 keV, 2.60 keV], much higher than in the nuclear spectrum. Hence these red and blue wings are extended in a few arcsecond scale, as confirmed by narrow-band X-ray imaging. These energies imply line-of-sight velocities of $\sim$19,000-42,000 km s$^{-1}$ for the red wing, and $\sim$ 28,000 km s$^{-1}$ for the blue wing, if the emission is due to neutral Fe K$\alpha$.
Abstract: 2302.00246
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Full Text: [ PostScript, PDF]
Title:Target of Opportunity Observations Detectability of Kilonovae with WFST
Download PDFAbstract: Kilonovae are approximately thermal transients, produced by mergers of binary neutron stars (BNSs) and NS-black hole binaries. As the optical counterpart of the gravitational wave event GW170817, AT2017gfo is the first kilonova detected with smoking-gun evidence. Its observation offers vital information for constraining the Hubble constant, the source of cosmic $r$-process enrichment, and the equation of state of neutron stars. The 2.5-meter Wide-Field Survey Telescope (WFST) operates at six bands (u, g, r, i, z, w), spanning from 320 to 925 nm. It will be completed in the first half of 2023, and with a field-of-view diameter of 3 degrees, aims to detect kilonovae in the near future. In this article, considering the influence of the host galaxies and sky brightness, we generate simulated images to investigate WFST's ability to detect AT2017gfo-like kilonovae. Due to their spectra, host galaxies can significantly impact kilonova detection at a longer wavelength. When kilonovae are at peak luminosity, we find that WFST performs better in the g and r bands and can detect 90\% (50\%) kilonovae at a luminosity distance of 248 Mpc (338 Mpc) with 30 s exposures. Furthermore, to reflect actual efficiency under target-of-opportunity observations, we calculate the total time of follow-up under various localization areas and distances. We find that if the localization areas of most BNS events detected during the fourth observing (O4) run of LIGO and Virgo are hundreds of deg$^2$, WFST is expected to find $\sim$30\% kilonovae in the first two nights during O4 period.
Abstract: 2301.11939
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Full Text: [ PostScript, PDF]
Title:Synchrotron Afterglow Model for AT 2022cmc: Jetted Tidal Disruption Event or Engine-Powered Supernova?
Download PDFAbstract: AT 2022cmc is a luminous optical transient ($\nu L_{\nu} \gtrsim 10^{45}$ erg s$^{-1}$) accompanied by decaying non-thermal X-rays (peak duration $t_{\rm X} \lesssim$ days and isotropic energy $E_{\rm X,iso} \gtrsim 10^{53}$ erg) and a long-lived radio/mm synchrotron afterglow, which has been interpreted as a jetted tidal disruption event (TDE). Both an equipartition analysis and a detailed afterglow model reveals the radio/mm emitting plasma to be expanding mildly relativistically (Lorentz factor $\Gamma \gtrsim\,few$) with an opening angle $\theta_{\rm j}\simeq0.1$ and roughly fixed energy $E_{\rm j,iso} \gtrsim few \times 10^{53}$ erg into an external medium of density profile $n \propto R^{-k}$ with $k \simeq 1.5-2$, broadly similar to that of the first jetted TDE candidate Swift J1644+57 and consistent with Bondi accretion at a rate $\sim 10^{-3}\dot{M}_{\rm Edd}$ onto a $10^{6}M_{\odot}$ black hole before the outburst. The rapidly decaying optical emission over the first days is consistent with fast-cooling synchrotron radiation from the same forward shock as the radio/mm emission, while the bluer slowly decaying phase to follow likely represents a separate thermal emission component. Emission from the reverse shock may have peaked during the first days, but whose non-detection in the optical band places an upper bound $\Gamma_{\rm j} \lesssim 100$ on the Lorentz factor of the unshocked jet. Although a TDE origin for AT 2022cmc is indeed supported by some observations, the vast difference between the short-lived jet activity phase $t_{\rm X} \lesssim$ days relative to the months-long thermal optical emission, also challenges this scenario. A stellar core-collapse event giving birth to a magnetar or black hole engine of peak duration $\sim 1$ day offers an alternative model also consistent with the circumburst environment, if interpreted as a massive-star wind.
Abstract: 2212.09769
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Full Text: [ PostScript, PDF]
Title:JWST's PEARLS: TN J1338-1942 -- I. Extreme jet triggered star-formation in a $z=4.11$ luminous radio galaxy
Download PDFAbstract: We present the first JWST observations of the $z=4.11$ luminous radio galaxy TN J1338-1942, obtained as part of the ``Prime Extragalactic Areas for Reionization and Lensing Science'' (``PEARLS'') project. Our NIRCam observations, designed to probe the key rest-frame optical continuum and emission line features at this redshift, enable resolved spectral energy distribution modelling that incorporates both a range of stellar population assumptions and radiative shock models. With an estimated stellar mass of $\log_{10}(M/\text{M}_{\odot}) \sim 10.9$, TN J1338--1942 is confirmed to be one of the most massive galaxies known at this epoch. Our observations also reveal extremely high equivalent-width nebular emission coincident with the luminous AGN jets that is best fit by radiative shocks surrounded by extensive recent star-formation. We estimate the total star-formation rate (SFR) could be as high as $\sim1600\,\text{M}_{\odot}\,\text{yr}^{-1}$, with the SFR that we attribute to the jet induced burst conservatively $\gtrsim500\,\text{M}_{\odot}\,\text{yr}^{-1}$. The mass-weighted age of the star-formation, $t_{\text{mass}} <4$ Myr, is consistent with the likely age of the jets responsible for the triggered activity and significantly younger than that measured in the core of the host galaxy. The extreme scale of the potential jet-triggered star-formation activity indicates the potential importance of positive AGN feedback in the earliest stages of massive galaxy formation, with our observations also illustrating the extraordinary prospects for detailed studies of high-redshift galaxies with JWST.
Abstract: 2212.09266
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Full Text: [ PostScript, PDF]
Title:Two-component jet model for multiwavelength afterglow emission of the extremely energetic burst GRB 221009A
Download PDFAbstract: Recently gamma-ray bursts (GRBs) have been detected at very high-energy (VHE) gamma-rays by imaging atmospheric Cherenkov telescopes, and a two-component jet model has often been invoked to explain multiwavelength data. In this work, multiwavelength afterglow emission from an extremely bright GRB, GRB 221009A, is examined. The isotropic-equivalent gamma-ray energy of this event is among the largest, which suggests that similarly to previous VHE GRBs, the jet opening angle is so small that the collimation-corrected gamma-ray energy is nominal. Afterglow emission from such a narrow jet decays too rapidly, especially if the jet propagates into uniform circumburst material. In the two-component jet model, another wide jet component with a smaller Lorentz factor dominates late-time afterglow emission, and we show that multiwavelength data of GRB 221009A can be explained by narrow and wide jets with opening angles similar to those employed for other VHE GRBs. We also discuss how model degeneracies can be disentangled with observations.
Abstract: 2211.05136
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Full Text: [ PostScript, PDF]
Title:Physics Beyond the Standard Model with Future X-ray Observatories: Projected Constraints on Very-Light Axion-Like Particles with $Athena$ and $AXIS$
Download PDFAbstract: Axion-Like Particles (ALPs) are well-motivated extensions of the Standard Model of Particle Physics and a generic prediction of some string theories. X-ray observations of bright Active Galactic Nuclei (AGN) hosted by rich clusters of galaxies are excellent probes of very-light ALPs, with masses $\mathrm{log}(m_\mathrm{a}/\mathrm{eV}) < -12.0$. We evaluate the potential of future X-ray observatories, particularly $Athena$ and the proposed $AXIS$, to constrain ALPs via observations of cluster-hosted AGN, taking NGC 1275 in the Perseus cluster as our exemplar. Assuming perfect knowledge of instrument calibration, we show that a modest exposure (200-ks) of NGC 1275 by $Athena$ permits us to exclude all photon-ALP couplings $g_\mathrm{a\gamma} > 6.3 \times 10^{-14} \ {\mathrm{GeV}}^{-1}$ at the 95% level, as previously shown by $Conlon \ et \ al. \ (2018)$, representing a factor of 10 improvement over current limits. We then proceed to assess the impact of realistic calibration uncertainties on the $Athena$ projection by applying a standard $Cash$ likelihood procedure, showing the projected constraints on $g_\mathrm{a\gamma}$ weaken by a factor of 10 (back to the current most sensitive constraints). However, we show how the use of a deep neural network can disentangle the energy-dependent features induced by instrumental miscalibration and those induced by photon-ALP mixing, allowing us to recover most of the sensitivity to the ALP physics. In our explicit demonstration, the machine learning applied allows us to exclude $g_\mathrm{a\gamma} > 2.0 \times 10^{-13} \ {\mathrm{GeV}}^{-1}$, complementing the projected constraints of next-generation ALP dark matter birefringent cavity searches for very-light ALPs. Finally, we show that a 200-ks $AXIS$/on-axis observation of NGC 1275 will tighten the current best constraints on very-light ALPs by a factor of 3.
Abstract: 2201.07494
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Full Text: [ PostScript, PDF]
Title:Spectral and polarization properties of reflected X-ray emission from black hole accretion discs
Download PDFAbstract: X-ray polarimetric missions planned for this decade will significantly enhance our knowledge of compact accreting sources. Observations of the X-ray polarization signal from active galactic nuclei (AGNs) or X-ray binary systems (XRBs) will bring new means to study inner accretion flow in these objects that, together with currently used spectroscopic and timing techniques, will help us to determine better their properties, such as their inclination, orientation, shape, and size of their corona as well as the black hole spin. In this work, we present a yet missing piece in the global polarization models of black hole accretion discs. We compute the reflected X-ray emission from the disc in a local co-moving frame using (1) the radiative transfer code TITAN to obtain the ionization structure of the disc and (2) the Monte Carlo code STOKES that incorporates the physics of absorption, re-emission, and Compton scattering to produce a complete spectropolarimetric output. We present the final Stokes parameters I, Q, and U for a set of photon-indices of the incident primary power-law radiation, the disc ionization parameters, incident and emission angles, for three independent polarization states of the incident coronal X-ray photons with a sufficient resolution in energy to allow for sharp discussion of spectral and polarization properties. We show that the spectral component matches well literature predictions. The polarization degree and angle are in agreement with analytical approximations previously appearing in reflection models and we demonstrate that the polarized reflected X-ray emission can be, locally, quite large in the 2-12 keV band.
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