Abstracts of Interest
Selected by:
Imogen Barnsley
Abstract: 2410.10294
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Title:Ten years of searching for relics of AGN jet feedback through RAD@home citizen science
View PDF HTML (experimental)Abstract:Understanding the evolution of galaxies cannot exclude the important role played by the central supermassive black hole and the circumgalactic medium (CGM). Simulations have strongly suggested the negative feedback of AGN Jet/wind/outflows on the ISM/CGM of a galaxy leading to the eventual decline of star formation. However, no "smoking gun" evidence exists so far where relics of feedback, observed in any band, are consistent with the time scale of a major decline in star formation, in any sample of galaxies. Relics of any AGN-driven outflows will be observed as a faint and fuzzy structure which may be difficult to characterise by automated algorithms but trained citizen scientists can possibly perform better through their intuitive vision with additional heterogeneous data available anywhere on the Internet. RAD@home, launched on 15th April 2013, is not only the first Indian Citizen Science Research (CSR) platform in astronomy but also the only CSR publishing discoveries using any Indian telescope. We briefly report 11 CSR discoveries collected over the last eleven years. While searching for such relics we have spotted cases of offset relic lobes from elliptical and spiral, episodic radio galaxies with overlapping lobes as the host galaxy is in motion, large diffuse spiral-shaped emission, cases of jet-galaxy interaction, kinks and burls on the jets, a collimated synchrotron thread etc. Such exotic sources push the boundaries of our understanding of classical Seyferts and radio galaxies with jets and the process of discovery prepares the next generation for science with the upgraded GMRT and Square Kilometre Array Observatory (SKAO).
Abstract: 2410.10204
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Title:A Multiwavelength Study of the Most Distant Gamma-ray Detected BL Lacertae Object 4FGL J1219.0+3653 ($z=3.59$)
View PDFAbstract:BL Lac objects are a class of jetted active galactic nuclei that do not exhibit or have weak emission lines in their optical spectra. Recently, the first $\gamma$-ray emitting BL Lac beyond $z=3$, 4FGL J1219.0 +3653 (hereafter J1219), was identified, i.e., within the first two billion years of the age of the universe. Here we report the results obtained from a detailed broadband study of this peculiar source by analyzing the new $\sim$58 ksec XMM-Newton and archival observations and reproducing the multiwavelength spectral energy distribution with the conventional one-zone leptonic radiative model. The XMM-Newton~data revealed that J1219 is a faint X-ray emitter ($F_{\rm 0.3-10~keV}=8.39^{+4.11}_{-2.40}\times10^{-15}$ erg/cm2/s) and exhibits a soft spectrum (0.3$-$10 keV photon index$=2.28^{+0.58}_{-0.48}$). By comparing the broadband physical properties of J1219 with $z>3$ $\gamma$-ray detected flat spectrum radio quasars (FSRQs), we have found that it has a relatively low jet power and, similar to FSRQs, the jet power is larger than the accretion disk luminosity. We conclude that deeper multiwavelength observations will be needed to fully explore the physical properties of this unique high-redshift BL Lac object.
Abstract: 2410.10357
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Title:Towards Searching for Photons with Energies beyond the PeV Range from Galactic PeVatrons
View PDF HTML (experimental)Abstract:Several gamma-ray observatories have discovered photons of cosmic origin with energies in the PeV ($10^{15}\,\text{eV}$) range. Photons at these energies might be produced as by-products from particle acceleration in so-called PeVatrons, which are widely assumed to be the sources of a large part of galactic cosmic rays. Based on recent measurements of these PeV $\gamma$-sources by LHAASO and HAWC, we extrapolate the energy spectra of selected sources up to the ultra-high-energy (UHE, ${\geq}10\,\text{PeV}$) regime. The goal of this study is to evaluate if (and under what conditions) giant air-shower observatories, for example the Pierre Auger Observatory, could contribute to testing the UHE luminosity of PeV $\gamma$-sources. Possible propagation effects are investigated as well as the required discrimination power to distinguish photon- and hadron-initiated air showers. For present detector setups, it turns out to be challenging to achieve the required sensitivity due to the energy threshold being too high or the detection area too small. Dedicated detector concepts appear to be needed to explore the UHE frontier. Ultimately, this could provide complementary information on the sources of cosmic rays beyond the PeV regime -- a key objective of current efforts in multimessenger astronomy.
Abstract: 2410.10396
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Title:Persistent GeV counterpart to the microquasar GRS 1915+105
View PDF HTML (experimental)Abstract:Microquasars are compact binary systems hosting collimated relativistic jets. They have long been proposed as cosmic-ray accelerators, probed via the gamma-ray emission produced by relativistic particles. However, the observational evidence is steadily increasing but limited: there are around twenty microquasars known to date, of which only three have so far been firmly detected in the GeV gamma-ray range, always in a flaring or special spectral state. Here we present Fermi-LAT observations of the region around the microquasar GRS 1915+105, which reveal the presence of previously unknown multi-GeV emission consistent with the position of the microquasar. No periodicity or variability is found, indicating a persistent source of gamma rays. The properties of the emission are consistent with a scenario in which protons accelerated in the jets interact with nearby gas and produce gamma rays. We find that if the jet has been operating at an average of 1% of the Eddington limit for 10% of the time that GRS 1915+105 spent in its current mass-transfer state, the transfer of 10% of the available power to protons is enough to reach the $\sim 3 \cdot 10^{49}$ erg required to explain the GeV signal. Therefore our results support a scenario in which microquasars with low-mass stellar companions act as hadronic accelerators, strengthening the idea that microquasars as a class contribute to at least some fraction of the observed cosmic-ray flux.
Abstract: 2410.11357
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Title:"My Earth" Astrophysics and Planets -- a serious game to build low carbon scenarios in the astronomy academic community
View PDFAbstract:This report summarizes what has happened in the mini-workshops entitled ''My Earth in 180 minutes'' organized during the lunch break at the SF2A 2024 conference in Marseille. The project showcased an innovative serious game designed to raise awareness of greenhouse gas (GHG) emissions in astronomical research laboratories. Participants, organized into teams, simulate strategies to reduce their carbon footprints by 50\%, focusing on key astronomical activities such as space instrumentation, data analysis, and laboratory work. The sessions highlight the challenges of achieving significant emissions reductions without disrupting core research activities, such as telescope observations. While the serious game facilitates important discussions on sustainable practices, the results point to the need for broader engagement, adaptation to different cultural contexts, and institutional support. The project highlights the importance of integrating climate action into the academic environment and suggests potential future directions for expanding its impact.
Abstract: 2410.11958
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Title:Pair production with capture by energetic cosmic ray nuclei in a photon background
View PDF HTML (experimental)Abstract:We investigate the ionization state of very energetic cosmic ray nuclei in photon fields, such as the cosmic microwave background (CMB) in extragalactic propagation and the environment surrounding the acceleration site in astrophysical sources. We focus on the process of pair production with electron capture (PPC), where the interaction of a single photon with a nucleus produces an $e^\pm$ pair (similar to Bethe-Heitler process) with the subsequent capture of electron by the nucleus. This process effectively reduces the nucleus charge by one unit and counteracts the photo-ionization process. We show that during cosmological propagation, where the ultra-high energy cosmic rays interact predominantly with the CMB, ionization dominates over PPC for all the cases of practical interest. However, within the source environment and at sufficiently high energies, ionization and PPC processes can reach an equilibrium, leading to a significant fraction of dressed heavy nuclei. This provides a further limitation to the acceleration of high-$Z$ nuclei to very high energies in environments with hot and dense photon fields.
Abstract: 2410.11984
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Title:Data-driven core collapse supernova multilateration with first neutrino events
View PDF HTML (experimental)Abstract:A Galactic core-collapse supernova (CCSN) is likely to be observed in neutrino detectors around the world minutes to hours before the electromagnetic radiation arrives. The SNEWS2.0 network of neutrino and dark matter detectors aims to use the relative arrival times of the neutrinos at the different experiments to point back to the supernova. One of the simplest methods to calculate the CCSN direction is to use the first neutrino events detected through the inverse beta decay (IBD) process, $\overline{\nu}_e p\rightarrow e^+n$. We will consider neutrino detectors sensitive to IBD interactions with low backgrounds. The difference in signal arrival times between a large and a small detector will be biased, however, with the first event at the smaller detector, on average, arriving later than that at the larger detector. This bias can be mitigated by using these first events in a data-driven approach without recourse to simulations or models. In this article, we demonstrate this method and its uncertainty estimate using pairs of detectors of different sizes and with different supernova distances. Finally, we use this method to calculate probability skymaps using four detectors (Super-Kamiokande, JUNO, LVD, and SNO+) and show that the calculated probabilities yield appropriate confidence intervals. The resulting skymaps should be useful for the multi-messenger community to follow up on the SNEWS2.0 Galactic CCSN neutrino alert.
Abstract: 2410.13071
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Title:Particle Acceleration Time due to Turbulent-Induced Magnetic Reconnection
View PDF HTML (experimental)Abstract:We numerically investigate a crucial parameter for understanding particle acceleration theory via turbulence-induced magnetic reconnection: the particle acceleration time. We examine particles accelerated either during the jet's dynamic evolution or in a post-processing, nearly stationary regime. We derive the particle acceleration time and compare it with theoretical predictions for both the Fermi and drift regimes identified in the simulations. In the Fermi regime, the acceleration time is expected to be independent of the particles' energy, for constant reconnection velocity, as energy increases exponentially with time. Conversely, we expect the reconnection acceleration time to depend on the current sheet's thickness and the reconnection velocity, a dependence recently revisited by xu and lazarian 2023. They identified three conditions for \(t_{acc}\). We tested these relations using statistical distributions of the current sheets' thickness and reconnection velocities in the turbulent jet over time. The resulting average value of \(t_{acc}\) was found to be nearly constant with particle energy. We compared this acceleration time with the average acceleration time derived directly from 50,000 particles accelerated in situ in the same relativistic jet. When considering a longer time interval for particle acceleration in a nearly stationary snapshot of the turbulent jet, we find that the acceleration time during the Fermi regime remains nearly independent of particle energy and aligns with the acceleration time theoretical relations up to the threshold energy, attained when the particles Larmor radius becomes as large as the thickness of the largest current sheets. Beyond this threshold, the acceleration regime shifts to the slower drift regime, showing strong energy dependence, as predicted. The results also indicate a clear dominance of the Fermi regime of acceleration.
Abstract: 2410.13148
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Title:Learning Efficient Representations of Neutrino Telescope Events
View PDF HTML (experimental)Abstract:Neutrino telescopes detect rare interactions of particles produced in some of the most extreme environments in the Universe. This is accomplished by instrumenting a cubic-kilometer volume of naturally occurring transparent medium with light sensors. Given their substantial size and the high frequency of background interactions, these telescopes amass an enormous quantity of large variance, high-dimensional data. These attributes create substantial challenges for analyzing and reconstructing interactions, particularly when utilizing machine learning (ML) techniques. In this paper, we present a novel approach, called om2vec, that employs transformer-based variational autoencoders to efficiently represent neutrino telescope events by learning compact and descriptive latent representations. We demonstrate that these latent representations offer enhanced flexibility and improved computational efficiency, thereby facilitating downstream tasks in data analysis.
Abstract: 2410.13484
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Title:Exploring the supernova remnant contribution to the first LHAASO source catalog via passively illuminated interstellar clouds
View PDF HTML (experimental)Abstract:Supernova remnants (SNRs) are considered as the most promising source class to account for the bulk of the Galactic cosmic-ray flux. Yet amongst the population of ultra-high energy (UHE) sources that has recently emerged, due to high-altitude particle detector experiments such as LHAASO and HAWC, remarkably few are associated with known SNRs. These observations might well indicate that the highest energy particles would escape the remnant early during the shock evolution as a result of its reduced confinement capabilities. This flux of escaping particles may then encounter dense targets (gas and dust) for hadronic interactions in the form of both atomic and molecular material such as interstellar clouds, thereby generating a UHE gamma-ray flux. We explore such a scenario here, considering known SNRs in a physically driven model for particle escape, and as coupled to molecular clouds in the Galaxy. Our analysis allows the investigation of SNR-illuminated clouds in coincidence with sources detected in the first LHAASO catalogue. Indeed, the illuminated interstellar clouds may contribute to the total gamma-ray flux from several unidentified sources, as we discuss here. Yet we nevertheless find that further detailed studies will be necessary to verify or refute this scenario of passive UHE gamma-ray sources in future.
Abstract: 2410.14079
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Title:PKS 2254+074: A Blazar in Likely Association with the Neutrino Event IceCube-190619A
View PDF HTML (experimental)Abstract:We report our study of the field of a $\simeq$0.2 PeV neutrino event IC-190619A. This neutrino belongs to Gold events, which more likely have an astrophysical origin. Among the two $\gamma$-ray sources within the neutrino's positional uncertainty region, we find that one of them, the BL-Lac--type blazar PKS~2254+074, had a $\gamma$-ray flare at the arrival time of the neutrino. The flare is determined to have lasted $\sim$2.5 yr in a 180-day binned light curve, constructed from the data collected with the Large Area Telescope (LAT) onboard {\it the Fermi Gamma-ray Space Telescope (Fermi)}. Accompanying the flare, optical and mid-infrared brightening is also seen. In addition, $\geq$10 GeV high energy photons from the source have been detected, suggesting a hardening of the emission during the flare. Given both the positional and temporal coincidence of PKS~2254+074 with IC-190619A, we suggest that this blazar is likely another member of a few recently identified (candidate) neutrino-emitting blazars.
Abstract: 2410.13173
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Title:Measurement of attenuation length of the muon content in extensive air showers from 0.3 to 30 PeV with LHAASO
View PDF HTML (experimental)Abstract:The attenuation length of the muon content in extensive air showers provides important information regarding the generation and development of air showers. This information can be used not only to improve the description of such showers but also to test fundamental models of hadronic interactions. Using data from the LHAASO-KM2A experiment, the development of the muon content in high-energy air showers was studied. The attenuation length of muon content in the air showers was measured from experimental data in the energy range from 0.3 to 30 PeV using the constant intensity cut method. By comparing the attenuation length of the muon content with predictions from high-energy hadronic interaction models (QGSJET-II-04, SIBYLL 2.3d, and EPOS-LHC), it is evident that LHAASO results are significantly shorter than those predicted by the first two models (QGSJET-II-04 and SIBYLL 2.3d) but relatively close to those predicted by the third model (EPOS-LHC). Thus, the LHAASO data favor the EPOS-LHC model over the other two models. The three interaction models confirmed an increasing trend in the attenuation length as the cosmic-ray energy increases.
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