Abstracts of Interest
Selected by:
Adila Abdul Halim
Abstract: 2502.10246
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Title:A new pulsating neutron star in the Ultraluminous X-ray source NGC 4559 X7?
View PDF HTML (experimental)Abstract:Ultraluminous X-ray sources (ULX) are extragalactic objects with X-ray luminosities above the Eddington limit for a 10 Msun black hole (BH). ULXs may host super-Eddington accreting neutron stars or stellar mass BH, although the exact proportion of the two populations is not yet known. We investigate the properties of the ULX NGC 4559 X7, which shows flux variability up to a factor of 5 on months-to-years and hours-to-days timescales. A flaring activity was also observed during the source highest flux epochs. Flares are unpredictable, with different durations and all flat-topped in flux. The latter suggests that, at the flare peaks, there is likely a common switch-off mechanism for the accretion onto the compact object. We analysed all the available XMM-Newton and Swift/XRT observations to investigate the spectral and temporal evolution of X7, looking for short and long-term variability. We look for long-term periodicities and for coherent signals through accelerated searches that included orbital corrections. We described the X7 spectra with two thermal components plus a cut-off powerlaw model. We found three well defined spectral states, where the spectral variability is mainly driven by the two harder components. In addition, a pulsed signal at 2.6-2.7s was detected in two XMM-Newton observations. The significance of these coherent signals is relatively weak but they are found in two different observations with the same parameter space for the orbital properties. If confirmed, it would imply a high spin-down of 1e-9 s/s, which could be extreme amongst the known pulsating ULXs. X7 would become a new extragalactic ULX pulsar. We discuss the spectral and temporal results of X7 in the context of super-Eddington accretion onto a stellar-mass compact object, in particular suggesting that the source might likely host a neutron star.
Abstract: 2502.12111
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Title:Insights from leptohadronic modelling of the brightest blazar flare
View PDF HTML (experimental)Abstract:The blazar 3C 454.3 experienced a major flare in November 2010 making it the brightest $\gamma$-ray source in the sky of the Fermi-LAT. We obtain seven daily consecutive spectral-energy distributions (SEDs) of the flare in the infra-red, optical, ultra-violet, X-ray and $\gamma$-ray bands with publicly available data. We simulate the physical conditions in the blazar and show that the observed SEDs are well reproduced in the framework of a "standing feature" where the position of the emitting region is almost stationary, located beyond the outer radius of the broad-line region and into which fresh blobs of relativistically moving magnetized plasma are continuously injected. Meanwhile, a model with a single "moving blob" does not describe the data well. We obtain a robust upper limit to the amount of high-energy protons in the jet of 3C 454.3 from the electromagnetic SED. We construct a neutrino light curve of 3C 454.3 and estimate the expected neutrino yield at energies $\geq 100$ TeV for 3C 454.3 to be up to $6 \times 10^{-3}$ $\nu_{\mu}$ per year. Finally, we extrapolate our model findings to the light curves of all Fermi-LAT flat-spectrum radio quasars. We find that next-generation neutrino telescopes are expected to detect approximately one multimessenger ($\gamma + \nu_{\mu}$) flare per year from bright blazars with neutrino peak energy in the hundreds TeV -- hundreds PeV energy range and show that the electromagnetic flare peak can precede the neutrino arrival by months to years.
Abstract: 2502.11888
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Title:Exploring the Most Extreme Gamma-Ray Blazars Using Broadband Spectral Energy Distributions
View PDF HTML (experimental)Abstract:Extreme high-synchrotron peaked blazars (EHSPs) are rare high-energy sources characterised by synchrotron peaks beyond 10$^{17}$ Hz in their spectral energy distributions (SEDs). Their extreme properties challenge conventional blazar emission models and provide a unique opportunity to test the limits of particle acceleration and emission mechanisms in relativistic jets. However, the number of identified EHSPs is still small, limiting comprehensive studies of their population and characteristics. This study aims to identify new EHSP candidates and characterise their emission properties. A sample of 124 $\gamma$-ray blazars is analysed, selected for their high synchrotron peak frequencies and $\gamma$-ray emission properties, with a focus on sources showing low variability and good broadband data coverage. Their SEDs are constructed using archival multi-wavelength data from the SSDC SED Builder service, supplemented with recent Swift-UVOT, Swift-XRT, and Fermi-LAT observations. The SEDs are modelled with a one-zone synchrotron/synchrotron-self-Compton framework, classifying sources by synchrotron peak frequency. We identify 66 new EHSP candidates, significantly expanding the known population. Their synchrotron peak frequencies are statistically higher than in previous studies, and they exhibit low Compton dominance, consistent with environments lacking strong external photon fields. A clear correlation between synchrotron peak frequency and the magnetic-to-kinetic energy density ratio is found, with the most extreme EHSPs nearing equipartition. Our analysis suggests that 9 high-synchrotron peaked/EHSPs could be observed by the Cherenkov Telescope Array Observatory (CTAO) at $>5\sigma$ (20 at $>3\sigma$) in 20-hour exposures, highlighting their potential to improve studies of extreme jet physics and cosmology.
Abstract: 2502.11834
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Title:Ultrahigh energy cosmic rays and neutrino flux models
View PDF HTML (experimental)Abstract:In this review we motivate ultrahigh energy neutrino searches and their connection to ultrahigh energy cosmic rays. We give an overview of neutrino production mechanisms and their potential sources. Several model-independent benchmarks of the ultrahigh energy neutrino flux are discussed. Finally, a brief discussion of approaches for model-dependent neutrino flux predictions are given, highlighting a few examples from the literature.
Abstract: 2502.11511
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Title:Signature of strange star as the central engine of GRB 240529A
View PDF HTML (experimental)Abstract:GRB 240529A is a long-duration gamma-ray burst (GRB) whose light curve of prompt emission is composed of a triple-episode structure, separated by quiescent gaps of tens to hundreds of seconds. More interestingly, its X-ray light curve of afterglow exhibits two-plateau emissions, namely, an internal plateau emission that is smoothly connected with a $\sim t^{-0.1}$ segment and followed by a $\sim t^{-2}$ power-law decay. The three episodes in the prompt emission, together with two plateau emissions in X-ray, are unique in the Swift era. They are very difficult to explain with the standard internal/external shock model by invoking a black hole central engine. However, it could be consistent with the prediction of a supramassive magnetar as the central engine, the physical process of phase transition from magnetar to strange star, as well as the cooling and spin-down of the strange star. In this paper, we propose that the first- and second-episode emissions in the prompt $\gamma-$ray of GRB 240529A are from the jet emission of a massive star collapsing into a supramassive magnetar and the re-activity of central engine, respectively. Then, the third-episode emission of prompt is attributed to the phase transition from a magnetar to a strange star. Finally, the first- and second-plateau emissions of the X-ray afterglow are powered by the cooling and spin-down of the strange star, respectively. The observational data of each component of GRB 240529A are roughly coincident with the estimations of the above physical picture.
Abstract: 2502.12883
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Title:Exploring Axion-Like Particle from observation of FSRQ Ton 599 by Fermi-LAT
View PDF HTML (experimental)Abstract:High energy photons traveling through astrophysical magnetic fields have the potential to undergo oscillations with axion-like particles (ALPs), resulting in modifications to the observed photon spectrum. High energy $\gamma-$ray sources with significant magnetic field strengths provide an ideal setting to investigate this phenomenon. Ton 599, a flat spectrum radio quasar with a magnetic field strength on the order of Gauss in its emission region, presents a promising opportunity for studying ALP-photon oscillations. In this study, we analyze the effects of ALP-photon oscillations on the $\gamma$-ray spectrum of Ton 599 as observed by Fermi-LAT. Our investigation considers the potential influences of the broad-line region and dusty torus on the $\gamma-$ray spectrum of Ton 599. We set the constraints on the ALP parameters at the $95\%$ confidence level, and find that the constraints on \(g_{a\gamma}\) can reach approximately \(2 \times 10^{-12}~\mathrm{GeV}^{-1}\) for \(m_a \sim 10^{9}~\mathrm{eV}\).
Abstract: 2502.13439
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Title:Neutrino Oscillation in Core Collapse Supernova: The Impact of Spacetime Geometry
View PDF HTML (experimental)Abstract:Neutrino flavor evolution inside a core-collapse supernova is a topic of active research. The core of a supernova is an intense source of neutrinos and antineutrinos. Self-interaction among neutrinos (as well as antineutrinos) gives rise to a rich phenomenology not seen in terrestrial situations. In studies of the dynamics of flavor evolution in such environments, the gravitational effects are generally ignored. Although the curvature outside a dense core does not deviate much from a flat space, the spin of the neutrinos can still couple to the torsion of the spacetime. These extra degrees of freedom of curved spacetime have interaction strengths that are proportional to the density of the neutrinos and the other fermions \cite{Chakrabarty:2019cau} \cite{Barick:2023qjq} as well as the coupling constants of the spin-torsion interaction. We have studied the effects of such interactions in flavor evolution inside a core-collapse supernova \cite{Ghose:Manuscript}. The self-interaction gets modified by the spin-torsion interaction and the oscillation dynamics is modified. We have seen that there are noticeable changes in the flavor dynamics when the neutrino density is uniform. We have also studied the effects of such interaction in a realistic core-collapse supernova (CCSN). As neutrino astronomy enters the precision era, this study will shed light on the potential of neutrino fluxes from CCSN to probe the neutrino-neutrino interaction.
Abstract: 2502.13332
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Title:Primordial black holes
View PDF HTML (experimental)Abstract:The possibility that dark matter could be primordial black holes is discussed with an emphasis on the most commonly studied inflationary dynamics that could have produced them.
Abstract: 2502.11434
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Title:The blazar PKS 0605-085 as the origin of the KM3-230213A ultra high energy neutrino event
View PDF HTML (experimental)Abstract:The KM3Net Collaboration has recently reported on the observation of a remarkable event KM3-230213A that could have been produced by an ultra high energy cosmic neutrino. The origin of this event is still unclear. In particular, the cosmogenic neutrino scenario is not favoured due to the non-observation of a similar event by the IceCube detector, and most galactic scenarios are disfavoured as well. We show that the blazar PKS 0605-085 is a viable source of the KM3-230213A event. In particular, even though this blazar is located at 2.4$^{\circ}$ from the KM3-230213A event, the association between the blazar and the event is not unlikely due to a sizable direction systematic uncertainty of $\approx 1.5^{\circ}$ reported by the KM3Net Collaboration. Furthermore, we show that the observation of a $\approx$72 PeV neutrino from PKS 0605-085 is entirely possible given that a $\approx$7.5 PeV neutrino could have been observed from another blazar TXS 0506+056. Finally, we consider $\gamma$-ray constraints on the number of observable neutrino events and show that for the case of the external photon field production mechanism these constraints could be relaxed due to the often-neglected effect of the isotropisation of the hadronically-produced electrons in the magnetic field of the blob. We encourage further multi-wavelength observations of the blazar PKS 0605-085.
Abstract: 2502.13093
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Title:On testing in-vacuo dispersion with the most energetic neutrinos: KM3-230213A case study
View PDF HTML (experimental)Abstract:The phenomenology of in-vacuo dispersion, an effect such that quantum properties of spacetime slow down particles proportionally to their energies, has been a very active research area since the advent of the Fermi telescope. One of the assumptions made in this 15-year effort is that the phenomenology of in-vacuo dispersion has a particle-energy sweet spot: the energy of the particle should be large enough to render the analysis immune to source-intrinsic confounding effects but still small enough to facilitate the identification of the source of the particle. We use the gigantic energy of KM3-230213A as an opportunity to challenge this expectation. For a neutrino of a few hundred PeVs a transient source could have been observed at lower energies several years earlier, even assuming the characteristic scale of in-vacuo dispersion to be close to the Planck scale. We report that GRB090401B is in excellent directional agreement with KM3-230213A, and we discuss a strategy of in-vacuo-dispersion analysis suitable for estimating the significance of KM3-230213A as a GRB090401B-neutrino candidate. The p-value resulting from our analysis (0.015) is not small enough to warrant any excitement, but small enough to establish the point that a handful of such coincidences would be sufficient to meaningfully test in-vacuo dispersion.
Abstract: 2502.12986
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Title:KM3-230213A: An Ultra-High Energy Neutrino from a Year-Long Astrophysical Transient
View PDF HTML (experimental)Abstract:The Km3NET collaboration has recently reported the detection of a neutrino event with energy in excess of 100 PeV. This detection is in 2.5-3$\sigma$ tension with the upper limit on the neutrino flux at this energy imposed by IceCube and the Pierre Auger Observatory, if the event is considered part of the diffuse all-sky neutrino flux. We explore an alternative possibility that the event originates from a flare of an isolated source. We show that the data of Km3NET, IceCube and the Pierre Auger Observatory are consistent with the possibility of a source flare of duration $T \lesssim 2$ yr with muon neutrino flux $F \approx 3\times 10^{-10}(1\mbox{ yr }/ T)$ erg cm$^{-2}$ s$^{-1}$. Constraints on the neutrino spectrum indicate that the protons responsible for the neutrino emission have a very hard spectrum in the $E_p\gtrsim 10^{19}$ eV energy range, or otherwise that the neutrinos are produced by photohadronic interactions with infrared photons. The all-sky rate of similar neutrino flaring sources is constrained to be $R\lesssim 0.4/$ yr.
Abstract: 2502.12070
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Title:KM3NeT Constraint on Lorentz-Violating Superluminal Neutrino Velocity
View PDF HTML (experimental)Abstract:Lorentz invariance is a fundamental symmetry of spacetime and foundational to modern physics. One of its most important consequences is the constancy of the speed of light. This invariance, together with the geometry of spacetime, implies that no particle can move faster than the speed of light. In this article, we present the most stringent neutrino-based test of this prediction, using the highest energy neutrino ever detected to date, KM3-230213A. The arrival of this event, with an energy of $220^{+570}_{-110}\,\text{PeV}$, sets a constraint on $\delta \equiv c_\nu^2-1 < 4\times10^{-22}$.
This page created: Mon Feb 24 01:56:36 ACDT 2025 by Adila Abdul Halim
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