Abstracts of Interest
Selected by:
Adnaan Thakur
Abstract: 2311.12005
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Title:A gamma ray study of Galactic PeVatron candidates LHAASO J1825-1236 and J1839-0545
Download PDFAbstract:Recent studies by LHAASO have shown the presence of high-luminosity PeVatrons in our Galaxy. We examine two notable sources, each consisting of two pulsars, detected by LHAASO. We study multimessenger emissions from these pulsars, including gamma rays and particles. We simulated particle propagation throughout the Galaxy using the GALPROP software, accounting for emission from energy losses due to spin-down. As a result, we present the particle spectra generated during this propagation phase along with the corresponding gamma ray emission. Furthermore, we used the Gammapy software to perform gamma ray measurements from these sources in anticipation of future analyses to be carried out with the CTA observatory, which is now under development. The results indicate that CTA may be able to observe these sources and demonstrate the significant influence of gamma rays produced by proton propagation on the high-energy gamma ray spectra.
Abstract: 2311.11760
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Title:Probing primordial black holes at high redshift with future gravitational wave detector
Download PDFAbstract:We analyze the detection prospects for potential Primordial Black Hole Binary (PBHB) populations buried in the Stellar-Origin Black Hole Binary (SOBHB) population inferred by the LVK collaboration. We consider different PBHB population scenarios and several future Gravitational Wave (GW) detectors. To separate the PBHB component from the SOBHB one, we exploit the prediction that the PBHB merger rate does not decline as fast as the SOBHB one at high redshift. However, only a tiny fraction of PBHB events may be resolved individually, and the sub-threshold events may yield an undetectable Stochastic GW Background (SGWB). For this reason, we determine the statistical significance of the PBHB contributions in the number of resolvable events seen in future Earth-based detectors and the SGWB measured at LISA. We find that the synergy between these probes will consistently help assess whether or not a sizeable PBHB population is present.
Abstract: 2311.12140
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Title:MeerKAT 1.3 GHz Observations of Supernova Remnants
Download PDFAbstract:We present full Stokes MeerKAT L band (856--1712\,MHz) observations of \chg{36} high latitude supernova remnants. Sensitive, high dynamic range images show a wealth of structure. G15.1$-$1.6 appears to be an HII region rather than an SNR. G30.7$-$2.0 consists of three background extragalactic sources which appear to form an arc when imaged with much lower resolution. At least half of the remnants in the sample contain ``blowouts'', or ``ears'' showing these to be a common feature. Analysis of the polarimetric data reveals details of the magnetic field structure in the emitting regions of the remnants as well as magnetized thermal plasma in front of polarized emission. The chance alignment of G327.6+14.6 with a background AGN with very extended polarized jets allows testing for the presence of Faraday effects in the interior of the remnant. Scant evidence of Faraday rotating material is found in the interior of this remnant.
Abstract: 2311.12124
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Title:Contact tracing of binary stars: Pathways to stellar mergers
Download PDFAbstract:Stellar mergers lead to diverse phenomena: rejuvenated blue stragglers, magnetised and peculiar stars, transients and nebulae. Using a grid of about 6000 detailed 1D binary evolution models (initial component masses of 0.5-20$\,\text{M}_{\odot}$ at solar metallicity), we investigate which initial binary-star configurations lead to contact and classical common-envelope (CE) phases and assess the likelihood of a subsequent merger. Considering rotation and tides, we identify five mechanisms leading to contact and mergers: runaway mass transfer, $\text{L}_{2}$-overflow, accretor expansion, tidally-driven orbital decay, and non-conservative mass transfer. At least 40% of mass-transferring binaries with initial primary masses of 5-20$\,\text{M}_{\odot}$ enter contact, with >12% and >19% likely merging and evolving into a classical CE phase, respectively. Classical CE evolution occurs in late Case-B and Case-C binaries for initial mass ratios $q_{\text{i}}$ < 0.15-0.35, stable mass transfer for larger $q_{\text{i}}$. Early Case-B binaries enter contact for $q_{\text{i}}$ < 0.15-0.35 and in initially wider Case-A binaries, this occurs for $q_{\text{i}}$ < 0.35. All initially closest Case-A systems form contact binaries. We predict that binaries entering contact with $q$ < 0.5 merge or detach on a thermal timescale, while those formed with $q$ > 0.5 lead to long-lived contact phases. The fact that contact binaries are almost exclusively observed with $q$ > 0.5 confirms our expectations. Our contact, merger and classical CE incidences are lower limits because the mass transfer in our models is non-conservative. In most binaries, the non-accreted mass cannot be ejected and may settle in disks or lead to contact phases and mergers. Overall, contact binaries are a frequent and fascinating result of binary mass transfer of which the exact outcomes still remain to be understood and explored further.
Abstract: 2311.12558
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Title:A Spatially resolved X-ray Polarization map of the Vela Pulsar Wind Nebula
Download PDFAbstract:In this paper, we present a full spatially resolved polarization map for the Vela Pulsar Wind Nebula (PWN) observed by IXPE. By employing effective background discrimination techniques, our results show a remarkably high degree of local polarization in the outskirt region, exceeding 60% (55%) with a probability of 95% (99%), which approaches the upper limit predicted by the synchrotron emission mechanism. The high degree of polarization suggests that the turbulent magnetic energy is at most 33% of the ordered one. In addition, the X-ray polarization map exhibits a toroidal magnetic field pattern that is consistent with the field revealed by radio observations across the entire nebula. This consistency reveals that the observed X-ray and radio emissions are radiated by electrons from the same magnetic field. Different from the Crab PWN, the consistency observed in the Vela PWN may be attributed to the interaction between the reverse shock of supernova blast wave and the PWN, which leads to a displacement between the synchrotron-cooled nebula and the fresh nebula close to the pulsar. These findings deepen our understanding of the structure and evolution of the Vela PWN, and the magnetohydrodynamic interaction in PWNe.
Abstract: 2311.12376
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Title:X-ray characterization of the pulsar PSR J1849$-$0001 and its wind nebula G32.64+0.53 associated with TeV sources detected by H.E.S.S., HAWC, Tibet AS$γ$, and LHAASO
Download PDFAbstract:We report on the X-ray emission properties of the pulsar PSR J1849$-$0001 and its wind nebula (PWN), as measured by Chandra, XMM-Newton, NICER, Swift, and NuSTAR. In the X-ray data, we detected the 38-ms pulsations of the pulsar up to $\sim$60 keV with high significance. Additionally, we found that the pulsar's on-pulse spectral energy distribution displays significant curvature, peaking at $\approx$60 keV. Comparing the phase-averaged and on-pulse spectra of the pulsar, we found that the pulsar's off-pulse emission exhibits a spectral shape that is very similar to its on-pulse emission. This characterization of the off-pulse emission enabled us to measure the $>$10 keV spectrum of the faint and extended PWN using NuSTAR's off-pulse data. We measured both the X-ray spectrum and the radial profiles of the PWN's brightness and photon index, and we combined these X-ray measurements with published TeV results. We then employed a multizone emission scenario to model the broadband data. The results of the modeling suggest that the magnetic field within the PWN is relatively low ($\approx 7\mu \rm G$) and that electrons are accelerated to energies $\stackrel{>}{_{\sim}}$400 TeV within this PWN. The electrons responsible for the TeV emission outside the X-ray PWN may propagate to $\sim$30 pc from the pulsar in $\sim$10 kyr.
Abstract: 2311.12369
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Title:The Rapid ASKAP Continuum Survey V: cataloguing the sky at 1367.5 MHz and the second data release of RACS-mid
Download PDFAbstract:The Australian SKA Pathfinder (ASKAP) has surveyed the sky at multiple frequencies as part of the Rapid ASKAP Continuum Survey (RACS). The first two RACS observing epochs, at 887.5 (RACS-low) and 1367.5 (RACS-mid) MHz, have been released (McConnell et al., 2020; Duchesne et al., 2023). A catalogue of radio sources from RACS-low has also been released, covering the sky south of declination +30$^\circ$ (Hale et al., 2021). With this paper, we describe and release the first set of catalogues from RACS-mid, covering the sky below declination +49$^\circ$. The catalogues are created in a similar manner to the RACS-low catalogue, and we discuss this process and highlight additional changes. The general purpose primary catalogue covering 36 200 deg$^2$ features a variable angular resolution to maximise sensitivity and sky coverage across the catalogued area, with a median angular resolution of 11.2" times 9.3". The primary catalogue comprises 3 105 668 radio sources, including those in the Galactic Plane (2 861 923 excluding Galactic latitudes of $|b|<5^\circ$) and we estimate the catalogue to be 95% complete for sources above 1.6 mJy. With the primary catalogue, we also provide two auxiliary catalogues. The first is a fixed-resolution, 25-arcsec catalogue approximately matching the sky coverage of the RACS-low catalogue. This 25-arcsec catalogue is constructed identically to the primary catalogue, except images are convolved to a less-sensitive 25-arcsec angular resolution. The second auxiliary catalogue is designed for time-domain science, and is the concatenation of source-lists from the original RACS-mid images with no additional convolution, mosaicking, or de-duplication of source entries to avoid losing time-variable signals. All three RACS-mid catalogues, and all RACS data products, are available through the CSIRO ASKAP Science Data Archive (CASDA).
Abstract: 2311.12982
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Title:How to distinguish white dwarf and neutron star X-ray binaries during their X-ray outbursts?
Download PDFAbstract:Neutron stars (NSs) and white dwarfs (WDs) are characterized by different geometric and physical properties, but their observed properties are often similar, making them difficult to distinguish. Therefore, it is desirable to search for their spectral features that could be easily identified from observations. We present spectral and timing signatures of NSs and WDs hosted in accreting X-ray binaries that can be easily identified from X-ray observations. We perform spectral and timing analysis of 4U~1636--53 and SS~Cygni, as typical representatives of such NS and WD binaries, based on their X-ray observations by RXTE, ASCA, Suzaku and BeppoSAX uising {\it Comptonization} spectral model. As a result, we formulate a criterion that makes it easy to distinguish NS from WD in such binaries: NS X-rays exhibits clear quasi-stable behavior with the index $\Gamma\to2$ and is characterized by quasi periodic oscillations (QPOs) at $\nu_{QPO} >0.5$~Hz, although WD X-rays is stable with $\Gamma \to1.85$ and is accompanied by QPOs at $\nu_{QPO}<0.05$~Hz during source outbursts. In addition, we revealed that in 4U~1636--53 the mHz QPOs anti-correlate with the plasma temperature, $T_e$ of Compton cloud (or the corona around a NS. This allowed us to associate mHz-QPOs with the corona dynamics during outburst cycle. The above index effect, now well established for 4U~1636--53 and SS~Cygni using extensive observations, has previously been found in other low-mass X-ray NS and WD binaries and agrees well with the criterion for distinguishing NSs and WDs presented here.
Abstract: 2311.13566
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Title:Exploring Physically-Motivated Models to Fit Gamma-Ray Burst Spectra
Download PDFAbstract:We explore fitting gamma-ray burst spectra with three physically-motivated models, and thus revisit the viability of synchrotron radiation as the primary source of GRB prompt emission. We pick a sample of 100 bright GRBs observed by the Fermi Gamma-ray Burst Monitor (GBM), based on their energy flux values. In addition to the standard empirical spectral models used in previous GBM spectroscopy catalogs, we also consider three physically-motivated models; (a) a Thermal Synchrotron model, (b) a Band model with a High-energy Cutoff, and (c) a Smoothly Broken Power Law (SBPL) model with a Multiplicative Broken Power Law (MBPL). We then adopt the Bayesian information criterion (BIC) to compare the fits obtained and choose the best model. We find that 42% of the GRBs from the fluence spectra and 23% of GRBs from the peak-flux spectra have one of the three physically-motivated models as their preferred one. From the peak-flux spectral fits, we find that the low-energy index distributions from the empirical model fits for long GRBs peak around the synchrotron value of -2/3, while the two low-energy indices from the SBPL+MBPL fits of long GRBs peak close to the -2/3 and -3/2 values expected for a synchrotron spectrum below and above the cooling frequency.
Abstract: 2310.19939
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Title:Exploring Neutrino Mass Orderings through Supernova Neutrino Detection
Download PDFAbstract:Core-collapse supernovae (SNs) are one of the most powerful cosmic sources of neutrinos, with energies of several MeV. The emission of neutrinos and antineutrinos of all flavors carries away the gravitational binding energy of the compact remnant and drives its evolution from the hot initial to the cold final states. Detecting these neutrinos from Earth and analyzing the emitted signals present a unique opportunity to explore the neutrino mass ordering problem. This research outlines the detection of neutrinos from SNs and their relevance in understanding the neutrino mass ordering. The focus is on developing a model-independent analysis strategy, achieved by comparing distinct detection channels in large underground detectors. The objective is to identify potential indicators of mass ordering within the neutrino sector. Additionally, a thorough statistical analysis is performed on the anticipated neutrino signals for both mass orderings. Despite uncertainties in supernova explosion parameters, an exploration of the parameter space reveals an extensive array of models with significant sensitivity to differentiate between mass orderings. The assessment of various observables and their combinations underscores the potential of forthcoming supernova observations in addressing the neutrino mass ordering problem.
Abstract: 2310.14255
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Title:High-energy Neutrinos from Merging Stellar-mass Black Holes in Active Galactic Nuclei Accretion Disk
Download PDFAbstract:A population of binary stellar-mass black hole (BBH) mergers are believed to occur embedded in the accretion disk of active galactic nuclei (AGNs). In this {\em Letter}, we demonstrate that the jets from these BBH mergers can propagate collimatedly within the disk atmosphere along with a forward shock and a reverse shock forming at the jet head. Efficient proton acceleration by these shocks is usually expected before the breakout, leading to the production of TeV$-$PeV neutrinos through interactions between these protons and electron-radiating photons via photon-meson production. AGN BBH mergers occurring in the outer regions of the disk are more likely to produce more powerful neutrino bursts. Taking the host AGN properties of the potential GW190521 electromagnetic (EM) counterpart as an example, one expects $\gtrsim1$ neutrino events detectable by IceCube if the jet is on-axis and the radial location of the merger is $R\gtrsim10^5R_{\rm{g}}$, where $R_{\rm{g}}$ is the gravitational radius of the supermassive BH. Neutrino bursts from AGN BBH mergers could be detected by IceCube following the observation of gravitational waves (GWs), serving as precursor signals before the detection of EM breakout signals. AGN BBH mergers are potential target sources for future joint GW, neutrino, and EM multi-messenger observations.
Abstract: 2307.12546
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Title:Fermi Large Area Telescope Fourth Source Catalog Data Release 4 (4FGL-DR4)
Download PDFAbstract:We present an incremental version (4FGL-DR4, for Data Release 4) of the fourth Fermi-LAT catalog containing 7194 gamma-ray sources. Based on the first 14 years of science data in the energy range from 50 MeV to 1 TeV, it uses the same analysis methods as the 4FGL-DR3 catalog did for 12 years of data, with only a few improvements. The spectral parameters, spectral energy distributions, light curves and associations are updated for all sources.
We add four new extended sources and modify two existing ones. Among the 6658 4FGL-DR3 sources, we delete 14 and change the localization of 10, while 26 are newly associated and two associations were changed. We add 546 point sources, among which 8 are considered identified and 228 have a plausible counterpart at other wavelengths. Most are just above the detection threshold, and 14 are transient sources below the detection threshold that can affect the light curves of nearby sources.
Abstract: 2307.10382
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Title:Neutrinos from GRB 221009A: producing ALPs and explaining LHAASO anomalous $γ$ event
Download PDFAbstract:We propose a novel explanation for the 18 TeV gamma ray from GRB 221009A observed by LHAASO. High-energy neutrinos are converted into axion-like particles (ALPs) via their interaction with the cosmic neutrino background. Subsequently, ALPs are converted into high-energy photons in the magnetic field of our galaxy. We compute the fluxes of neutrinos, ALPs, and photons reaching Earth. IceCube's constraints on the neutrino flux from GRB 221009A translate into a severe upper bound on the photon flux. We find a range of parameters where all existing bounds are satisfied and the 18 TeV LHAASO photon can be explained. In the future, the specific correlation between the photon and neutrino flux reaching Earth from powerful neutrino sources with energies larger than 10 TeV such as GRBs or AGNs, can be used as a tool to differentiate our explanation from the alternatives suggested in the literature. We discuss how the interactions of our scenario can be embedded within electroweak gauge-invariant models, avoiding various cosmological and terrestrial bounds. We comment on the possibility of explaining the 251 TeV photon observed by the Carpet-2 detector, taking into account the bounds from the observation of high-energy neutrinos from TXS 0506+056.
Abstract: 2306.02248
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Title:Spectral and Jet Properties of the Quasi-thermal Dominated GRB 210121A, GRB 210610B and GRB 221022B
Download PDFAbstract:Some quasi-thermal (QT) dominated gamma-ray bursts (GRBs) could be well described by a multi-color blackbody (BB) function or a combined model of BB plus non-thermal (NT) component. In this analysis, two QT radiation-dominated bursts with known emission properties (GRB 210610B likely from a hybrid jet, and GRB 210121A with a spectrum consistent with a non-dissipative photospheric emission from a pure hot fireball) are used to make a comparison between these two modelings. To diagnose the magnetization properties of the central engine, the `top-down' approach proposed by Gao \& Zhang is adopted. It is found that diagnoses based on these two modelings could provide similar conclusions qualitatively; however, the modeling with mBB (or mBB+NT) may give more reasonable physical explanations. This implies that impacts from the GRB jet structure and the geometrical broadening on the observed spectrum should be considered. However, conservatively, these methods may be not sensitive enough to distinguish between the pure hot fireball and a mildly magnetized hybrid jet. Some other information is necessary to provide more evidence for the determination of jet properties for similar GRBs. Based on these considerations, we suggest that the photospheric emission of GRB 221022B is from a hot jet; a dissipation is caused by a internal shock (IS) mechanism due to the increasing Lorentz Factor with time, which makes its prompt emission behaves a typical evolution from thermal to NT.
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