Abstracts of Interest
Selected by:
Simon
Abstract: 2307.05301
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Title:Signal-background separation and energy reconstruction of gamma rays using pattern spectra and convolutional neural networks for the Small-Sized Telescopes of the Cherenkov Telescope Array
Download PDFAbstract: Imaging Atmospheric Cherenkov Telescopes (IACTs) detect very high-energy gamma rays from ground level by capturing the Cherenkov light of the induced particle showers. Convolutional neural networks (CNNs) can be trained on IACT camera images of such events to differentiate the signal from the background and to reconstruct the energy of the initial gamma ray. Pattern spectra provide a 2-dimensional histogram of the sizes and shapes of features comprising an image and they can be used as an input for a CNN to significantly reduce the computational power required to train it. In this work, we generate pattern spectra from simulated gamma-ray and proton images to train a CNN for signal-background separation and energy reconstruction for the Small-Sized Telescopes (SSTs) of the Cherenkov Telescope Array (CTA). A comparison of our results with a CNN directly trained on CTA images shows that the pattern spectra-based analysis is about a factor of three less computationally expensive but not able to compete with the performance of the CTA images-based analysis. Thus, we conclude that the CTA images must be comprised of additional information not represented by the pattern spectra.
Abstract: 2307.05177
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Title:Development of a SiPM Pixel Prototype for the Large-Sized Telescope of the Cherenkov Telescope Array
Download PDFAbstract: The Cherenkov Telescope Array (CTA) will be the next generation ground-based gamma-ray observatory. CTA consists of different telescope types of which the largest ones (Large-Sized Telescopes, LSTs) cover the lower energy range, between 20 GeV and 200 GeV. The first LST is currently being commissioned at the Roque de los Muchachos Observatory, La Palma, Canary Islands. Its camera has 1855 photomultipliers (PMTs) with 1.5 inch cathodes. Silicon Photomultipliers (SiPMs) are increasingly becoming valid alternatives to PMTs also in gamma-ray astronomy. In the context of the LST project, there is an effort to study a novel Advanced Camera, equipped with SiPMs and a completely redesigned electronics based on a fully digital approach. To study and develop solutions on the sensors of these camera, we built a prototype camera module with a fully re-designed pre-amplifying stage and sensor bias control while re-using the digitizing and triggering stages of the existing LST camera module. We report on the design choices made to achieve the highest performance in terms of timing and charge resolution and the laboratory measurements validating those choices.
Abstract: 2307.04427
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Title:Observation of high-energy neutrinos from the Galactic plane
Download PDFAbstract: The origin of high-energy cosmic rays, atomic nuclei that continuously impact Earth's atmosphere, has been a mystery for over a century. Due to deflection in interstellar magnetic fields, cosmic rays from the Milky Way arrive at Earth from random directions. However, near their sources and during propagation, cosmic rays interact with matter and produce high-energy neutrinos. We search for neutrino emission using machine learning techniques applied to ten years of data from the IceCube Neutrino Observatory. We identify neutrino emission from the Galactic plane at the 4.5$\sigma$ level of significance, by comparing diffuse emission models to a background-only hypothesis. The signal is consistent with modeled diffuse emission from the Galactic plane, but could also arise from a population of unresolved point sources.
Abstract: 2307.03259
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Title:On the Neutrino and Gamma-Ray Emission from NGC 1068
Download PDFAbstract: IceCube has recently reported the detection of $\sim 1-10 \,{\rm TeV}$ neutrinos from the nearby active galaxy, NGC 1068. The lack of TeV-scale emission from this source suggests that these neutrinos are generated in the dense corona that surrounds NGC 1068's supermassive black hole. In this paper, we present a physical model for this source, including the processes of pair production, pion production, synchrotron, and inverse Compton scattering. We have also performed a new analysis of Fermi-LAT data from the direction of NGC 1068, finding that the gamma-ray emission from this source is very soft but bright at energies below $\sim 1 \, {\rm GeV}$. Our model can predict a gamma-ray spectrum that is consistent with Fermi-LAT observations, but only if the magnetic field within the corona of this active galactic nucleus (AGN) is quite high, namely $B\gtrsim 6 \, {\rm kG}$. To explain the observed neutrino emission, this source must accelerate protons with a total power that is comparable to its intrinsic X-ray luminosity. In this context, we consider two additional nearby active galaxies, NGC 4151 and NGC 3079, which have been identified as promising targets for IceCube.
Abstract: 2307.02372
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Title:Multi-messenger observations support cosmic ray interactions surrounding acceleration sources
Download PDFAbstract: The observations of the energy spectra of cosmic-ray have revealed complicated structures. Especially, spectral hardenings in the boron-to-carbon and boron-to-oxygen ratios above $\sim 200$ GV has been revealed by AMS-02 and DAMPE experiments. One scenario to account for the hardenings of secondary-to-primary ratios is the nuclear fragmentation of freshly accelerated particles around sources. In this work, we further study this scenario based on new observations of Galactic diffuse gamma rays by LHAASO and neutrinos by IceCube. We find that the spectra of cosmic ray nuclei, the diffuse ultra-high-energy gamma rays, and the Galactic component of neutrinos can be simultaneously explained, given an average confinement and interaction time of $\sim 0.25$ Myr around sources. These multi-messenger data thus provide evidence of non-negligible grammage of Galactic cosmic rays surrounding sources besides the traditional one during the propagation.
Abstract: 2307.02538
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Title:Searches for dark matter decay with ultra-high-energy neutrinos endure backgrounds
Download PDFAbstract: Next-generation ultra-high-energy (UHE) neutrino telescopes, presently under planning, will have the potential to probe the decay of heavy dark matter (DM) into UHE neutrinos, with energies in excess of $10^7$~GeV. Yet, this potential may be deteriorated by the presence of an unknown background of UHE neutrinos, cosmogenic or from astrophysical sources, not of DM origin and seemingly large enough to obscure the DM signature. We show that leveraging the angular and energy distributions of detected events safeguards future searches for DM decay against such backgrounds. We focus on the radio-detection of UHE neutrinos in the planned IceCube-Gen2 neutrino telescope, which we model in state-of-the-art detail. We report promising prospects for the discovery potential of DM decay into UHE neutrinos, the measurement of DM mass and lifetime, and limits on the DM lifetime, despite the presence of a large background, without prior knowledge of its size and shape.
Abstract: 2307.04194
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Title:A Search for AGN sources of the IceCube Diffuse Neutrino Flux
Download PDFAbstract: The origin of the diffuse astrophysical neutrino flux measured by the IceCube Observatory remains largely unknown. Although NGC 1068 and TXS 0506+056 have been identified as potential neutrino sources, the diffuse flux of neutrinos must have additional sources that have not yet been identified. Here we investigate potential correlations between IceCube's neutrino events and the Fermi and MOJAVE source catalogs, using the publicly-available IceCube data set. We perform three separate spatially-dependent, energy-dependent, and time-dependent searches, and find no statistically significant sources outside of NGC 1068. We find that no more than 13% of IceCube's neutrino flux originates from blazars over the whole sky. Then, using an energy-dependent likelihood analysis, the limit on neutrinos originating from blazars reduces to 9% in the Northern hemisphere. Finally, we set limits on individual sources from the MOJAVE radio catalog after finding no statistically significant time-flaring sources.
Abstract: 2307.02905
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Title:Decomposing the Origin of TeV-PeV Emission from the Galactic Plane: Implications of Multi-messenger Observations
Download PDFAbstract: High-energy neutrino and $\gamma$-ray emission has been observed from the Galactic plane, which may come from individual sources and/or diffuse cosmic rays. We evaluate the contribution of these two components through the multi-messenger connection between neutrinos and $\gamma$ rays in hadronic interactions. We derive maximum fluxes of neutrino emission from the Galactic plane using $\gamma$-ray catalogs, including 4FGL, HGPS, 3HWC, and 1LHAASO, and measurements of the Galactic diffuse emission by Tibet AS$\gamma$ and LHAASO. We find that depending on model templates, the diffuse emission is brighter than the sum of resolved sources when excluding promising leptonic sources such as pulsars, pulsar wind nebulae, and TeV halos. Our result indicates that the Galactic neutrino emission observed by the IceCube Collaboration may be dominated by the Galactic diffuse emission or unresolved $\gamma$-ray sources. Future observations of neutrino telescopes and air-shower $\gamma$-ray experiments in the Southern hemisphere are needed to accurately disentangle the source and diffuse emission of the Milky Way.
Abstract: 2307.03191
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Title:Where shadows lie: reconstruction of anisotropies in the neutrino sky
Download PDFAbstract: The Cosmic Neutrino Background (CNB) encodes a wealth of information, but has not yet been observed directly. To determine the prospects of detection and to study its information content, we reconstruct the phase-space distribution of local relic neutrinos from the three-dimensional distribution of matter within 200 Mpc/h of the Milky Way. Our analysis relies on constrained realization simulations and forward modelling of the 2M++ galaxy catalogue. We find that the angular distribution of neutrinos is anti-correlated with the projected matter density, due to the capture and deflection of neutrinos by massive structures along the line of sight. Of relevance to tritium capture experiments, we find that the gravitational clustering effect of the large-scale structure on the local number density of neutrinos is more important than that of the Milky Way for neutrino masses less than 0.1 eV. Nevertheless, we predict that the density of relic neutrinos is close to the cosmic average, with a suppression or enhancement over the mean of (-0.3%, +7%, +27%) for masses of (0.01, 0.05, 0.1) eV. This implies no more than a marginal increase in the event rate for tritium capture experiments like PTOLEMY. We also predict that the CNB and CMB rest frames coincide for 0.01 eV neutrinos, but that neutrino velocities are significantly perturbed for masses larger than 0.05 eV. Regardless of mass, we find that the angle between the neutrino dipole and the ecliptic plane is small, implying a near-maximal annual modulation in the bulk velocity. Along with this paper, we publicly release our simulation data, comprising more than 100 simulations for six different neutrino masses.
Abstract: 2307.02976
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Title:Future developments in ground-based gamma-ray astronomy
Download PDFAbstract: Ground-based gamma-ray astronomy is a powerful tool to study cosmic-ray physics, providing a diagnostic of the high-energy processes at work in the most extreme astrophysical accelerators of the universe. Ground-based gamma-ray detectors apply a number of experimental techniques to measure the products of air showers induced by the primary gamma-rays over a wide energy range, from about 30 GeV to few PeV. These are based either on the measurement of the atmospheric Cherenkov light induced by the air showers, or the direct detection of the shower's secondary particles at ground level. Thanks to the recent development of new and highly sensitive ground-based gamma-ray detectors, important scientific results are emerging which motivate new experimental proposals, at various stages of implementation. In this chapter we will present the current expectations for future experiments in the field.
Abstract: 2307.01596
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Title:Cosmic rays from star clusters
Download PDFAbstract: Massive stars blow powerful winds and eventually explode as supernovae. By doing so, they inject energy and momentum in the circumstellar medium, which is pushed away from the star and piles up to form a dense and expanding shell of gas. The effect is larger when many massive stars are grouped together in bound clusters or associations. Large cavities form around clusters as a result of the stellar feedback on the ambient medium. They are called superbubbles and are characterised by the presence of turbulent and supersonic gas motions. This makes star clusters ideal environments for particle acceleration, and potential contributors to the observed Galactic cosmic ray intensity.
Abstract: 2307.03477
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Title:Probing star clusters as cosmic ray factories
Download PDFAbstract: Stellar clusters (SC) are fundamental building blocks of galaxies and are among the most studied astronomical objects in the Cosmos. The recent association of diffuse $\gamma$-ray emission detected by different experiments with a dozen young SCs suggests the presence of some process able to accelerate particles at least up to hundreds of TeV. In this Ph.D. thesis, we investigate the capability of young massive stellar clusters (YMSC) to produce cosmic rays under the assumption that particles are accelerated at the cluster wind termination shock. The study is divided into three parts. First, we focus on the specific case of Cygnus OB2. We model the observed $\gamma$-ray emission (in a pure hadronic scenario) assuming different models for particle propagation in the neighborhood of the cluster. We found that particles accelerated by Cygnus OB2 can account for both the $\gamma$-ray spectrum and the radial morphology at very high energy. In the second part, we compute the diffuse $\gamma$-ray emission expected by the unresolved population of Galactic YMSC. For this purpose, we build a synthetic population of YMSC based on the properties of local SC. Under the assumption of a pure hadronic emission, we found that YMSCs can significantly contribute to the observed diffuse $\gamma$-ray emission at a few TeV. The final part of the work is dedicated to understand the impact of CRs produced by SCs on the ionization rate of molecular clouds close to those SCs. We found that the ionization rate can significantly differ from the expected value in clouds located in the unperturbed interstellar medium. We show that the measured value of ionization rate, paired with $\gamma$-ray observations, can be used to constrain particle diffusion in the vicinity of the stellar cluster.
Abstract: 2307.02907
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Title:Constraining the cosmic-ray mass composition by measuring the shower length with SKA
Download PDFAbstract: The current generation of air shower radio arrays has demonstrated that the atmospheric depth of the shower maximum Xmax can be reconstructed with high accuracy. These experiments are now contributing to mass composition studies in the energy range where a transition from galactic to extragalactic cosmic-ray sources is expected. However, we are still far away from an unambiguous interpretation of the data. Here we propose to use radio measurements to derive a new type of constraint on the mass composition, by reconstructing the shower length L. The low-frequency part of the Square Kilometer Array will have an extremely high antenna density of roughly 60.000 antennas within one square kilometer, and is the perfect site for high-resolution studies of air showers. In this contribution, we discuss the impact of being able to reconstruct L, and the unique contribution that SKA can make to cosmic-ray science.
Abstract: 2307.02068
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Title:Properties of secondary components in extensive air shower of cosmic rays in knee energy region
Download PDFAbstract: The knee of cosmic ray spectra reflects the maximum energy accelerated by galactic cosmic ray sources or the limit to the ability of galaxy to bind cosmic rays. The measuring of individual energy spectra is a crucial tool to ascertain the origin of the knee. The Extensive Air Shower of cosmic rays in the knee energy region is simulated via CORSIKA software. The energy resolution for different secondary components and primary nuclei identification capability are studied. The energy reconstruction by using electromagnetic particles in the energy around knee is better than by using other secondary particles. The resolution is 10-19 percent for proton, and 4-8 percent for iron. For the case of primary nuclei identification capability, the discriminability of density of muons is best both at low (around 100 TeV) and high (around 10 PeV) energy, the discriminability of the shape of lateral distribution of electron and gamma-rays are good at low energy and the discriminability of density of neutrons is good at high energy. The differences between the lateral distributions of secondary particles simulated by EPOS-LHC and QGSJet-II-04 hadronic model are also studied. The results in this work can provide important information for selecting the secondary components and detector type during energy reconstruction and identifying the primary nuclei of cosmic rays in the knee region.
Abstract: 2307.02125
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Title:3HWC J0631+107/LHAASO J0631+1040: a TeV halo powered by the pulsar J0631+1036?
Download PDFAbstract: PSR~J0631+1036 is a middle-aged pulsar with properties similar to those of the nearby Geminga pulsar. It is bright in $\gamma$-rays, and has been noted as the only source possibly associated with the TeV source 3HWC J0631+107 (also the LHAASO J0631+1040). For understanding the nature of the TeV source, we analyze the GeV $\gamma$-ray data obtained with the Large Area Telescope (LAT) onboard {\it the Fermi Gamma-ray Space Telescope} for the source region. We are able to remove the pulsar's emission from the region from timing analysis, and find that the region is rather clean without possible GeV $\gamma$-ray emission present as the counterpart to the TeV source. By comparing this pulsar to Geminga and considering the spectral feature of the TeV source, we argue that it is likely the TeV halo powered by the pulsar.
Abstract: 2307.02098
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Title:JWST detection of heavy neutron capture elements in a compact object merger
Download PDFAbstract: The mergers of binary compact objects such as neutron stars and black holes are of central interest to several areas of astrophysics, including as the progenitors of gamma-ray bursts (GRBs), sources of high-frequency gravitational waves and likely production sites for heavy element nucleosynthesis via rapid neutron capture (the r-process). These heavy elements include some of great geophysical, biological and cultural importance, such as thorium, iodine and gold. Here we present observations of the exceptionally bright gamma-ray burst GRB 230307A. We show that GRB 230307A belongs to the class of long-duration gamma-ray bursts associated with compact object mergers, and contains a kilonova similar to AT2017gfo, associated with the gravitational-wave merger GW170817. We obtained James Webb Space Telescope mid-infrared (mid-IR) imaging and spectroscopy 29 and 61 days after the burst. The spectroscopy shows an emission line at 2.15 microns which we interpret as tellurium (atomic mass A=130), and a very red source, emitting most of its light in the mid-IR due to the production of lanthanides. These observations demonstrate that nucleosynthesis in GRBs can create r-process elements across a broad atomic mass range and play a central role in heavy element nucleosynthesis across the Universe.
Abstract: 2307.01919
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Title:Black Holes as a Collider of High Energy Particles
Download PDFAbstract: According to the Banados-Silk-West (BSW) process, rotating black holes can act as particle colliders capable of achieving arbitrarily high center-of-mass energy (CME), provided that a specific angular momentum of one of the particles is present. In this discussion, we demonstrate that both Kerr black holes and Schwarzschild black holes could serve as potential sources of high-energy particles in the polar region.
Abstract: 2307.03097
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Title:Close Encounters of Star - Black Hole Binaries with Single Stars
Download PDFAbstract: Multi-body dynamical interactions of binaries with other objects are one of the main driving mechanisms for the evolution of star clusters. It is thus important to bring our understanding of three-body interactions beyond the commonly employed point-particle approximation. To this end we here investigate the hydrodynamics of three-body encounters between star-black hole (BH) binaries and single stars, focusing on the identification of final outcomes and their long-term evolution and observational properties, using the moving-mesh hydrodynamics code AREPO. This type of encounters produces five types of outcomes: stellar disruption, stellar collision, weak perturbation of the original binary, binary member exchange, and triple formation. The two decisive parameters are the binary phase angle, which determines which two objects meet at the first closest approach, and the impact parameter, which sets the boundary between violent and non-violent interactions. When the impact parameter is smaller than the semimajor axis of the binary, tidal disruptions and star-BH collisions frequently occur when the BH and the incoming star first meet, while the two stars mostly merge when the two stars meet first instead. In both cases, the BHs accrete from an accretion disk at super-Eddington rates, possibly generating flares luminous enough to be observed. The stellar collision products either form a binary with the BH or remain unbound to the BH. Upon collision, the merged stars are hotter and larger than main sequence stars of the same mass at similar age. Even after recovering their thermal equilibrium state, stellar collision products, if isolated, would remain hotter and brighter than main sequence stars until becoming giants.
Abstract: 2307.01277
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Title:X-ray metal line emission from the hot circumgalactic medium: probing the effects of supermassive black hole feedback
Download PDFAbstract: We derive predictions from state-of-the-art cosmological galaxy simulations for the spatial distribution of the hot circumgalactic medium (CGM, ${\rm [0.1-1]R_{200c}}$) through its emission lines in the X-ray soft band ($[0.3-1.3]$ keV). In particular, we compare IllustrisTNG, EAGLE, and SIMBA and focus on galaxies with stellar mass $10^{10-11.6}\, \MSUN$ at $z=0$. The three simulation models return significantly different surface brightness radial profiles of prominent emission lines from ionized metals such as OVII(f), OVIII, and FeXVII as a function of galaxy mass. Likewise, the three simulations predict varying azimuthal distributions of line emission with respect to the galactic stellar planes, with IllustrisTNG predicting the strongest angular modulation of CGM physical properties at radial range ${\gtrsim0.3-0.5\,R_{200c}}$. This anisotropic signal is more prominent for higher-energy lines, where it can manifest as X-ray eROSITA-like bubbles. Despite different models of stellar and supermassive black hole (SMBH) feedback, the three simulations consistently predict a dichotomy between star-forming and quiescent galaxies at the Milky-Way and Andromeda mass range, where the former are X-ray brighter than the latter. This is a signature of SMBH-driven outflows, which are responsible for quenching star formation. Finally, we explore the prospect of testing these predictions with a microcalorimeter-based X-ray mission concept with a large field-of-view. Such a mission would probe the extended hot CGM via soft X-ray line emission, determine the physical properties of the CGM, including temperature, from the measurement of line ratios, and provide critical constraints on the efficiency and impact of SMBH feedback on the CGM.
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