Abstracts of Interest
Selected by:
Adila Abdul Halim
Abstract: 2205.10267
Full Text: [ PostScript, PDF]
Full Text: [ PostScript, PDF]
Title:Reproducibility of the First Image of a Black Hole in the Galaxy M87 from the Event Horizon Telescope (EHT) Collaboration
Download PDFAbstract: This paper presents an interdisciplinary effort aiming to develop and share sustainable knowledge necessary to analyze, understand, and use published scientific results to advance reproducibility in multi-messenger astrophysics. Specifically, we target the breakthrough work associated with the generation of the first image of a black hole, called M87. The image was computed by the Event Horizon Telescope Collaboration. Based on the artifacts made available by EHT, we deliver documentation, code, and a computational environment to reproduce the first image of a black hole. Our deliverables support new discovery in multi-messenger astrophysics by providing all the necessary tools for generalizing methods and findings from the EHT use case. Challenges encountered during the reproducibility of EHT results are reported. The result of our effort is an open-source, containerized software package that enables the public to reproduce the first image of a black hole in the galaxy M87.
Abstract: 2205.10384
Full Text: [ PostScript, PDF]
Full Text: [ PostScript, PDF]
Title:Oscillations of High-Energy Cosmic Neutrinos in the Copious MeV Neutrino Background
Download PDFAbstract: The core-collapse of massive stars and merger of neutron star binaries are among the most promising candidate sites for the production of high-energy cosmic neutrinos. We demonstrate that the high-energy neutrinos produced in such extreme environments can experience efficient flavor conversions on scales much shorter than those expected in vacuum, due to their coherent forward scatterings with the bath of decohered low-energy neutrinos emitted from the central engine. These low-energy neutrinos, which exist as mass eigenstates, provide a very special and peculiar dominant background for the propagation of the high-energy ones. We point out that the high-energy neutrino flavor ratio is modified to a value independent of neutrinos energies, which is distinct from the conventional prediction with the matter effect. We also suggest that the signals can be used as a novel probe of new neutrino interactions beyond the Standard Model. This is yet another context where neutrino-neutrino interactions can play a crucial role in their flavor evolution.
Abstract: 2205.10618
Full Text: [ PostScript, PDF]
Full Text: [ PostScript, PDF]
Title:Galactic Kites
Download PDFAbstract: I show that interstellar films of material thinner than a micron, drift away from the Galactic plane as a result of stellar radiation pressure. Such films, whether produced naturally by dust coagulation in proto-planetary disks or artificially by technological civilizations, would accumulate over the age of the Milky-Way and hover above the Galactic disk at a scale-height set gravitationally by the dark matter halo. Limits on scattered starlight imply that this population carries a fraction below 2x10^{-3} of the interstellar medium mass.
Abstract: 2205.10774
Full Text: [ PostScript, PDF]
Full Text: [ PostScript, PDF]
Title:X- and Gamma-ray astrophysics in the era of Multi-messenger astronomy
Download PDFAbstract: Multi-messenger astronomy is becoming a major avenue to explore the Universe. Several well known astrophysical sources are also expected to emit other 'messenger' than photons: namely cosmic rays, gravitational waves and neutrinos. These additional messengers bring complementary pieces of information to the ones carried by electromagnetic radiation and concur to draw a complete phenomenological picture of several astrophysical events as well as to measure key cosmological parameters. Indeed, it is widely believed in the astronomical community that several aspects of fundamental physics and cosmology will be unveiled only within the framework of multi-messenger astronomy. The most recent breakthrough discoveries of a gravitational wave source associated with a short gamma-ray burst, and of a neutrino event found to be spatially consistent with a flaring blazar, have already shown the key role that high-energy sources will play in multi-messenger observations. The first part of this chapter provides a description of the main properties of gamma-ray bursts, blazars, and other high-energy sources from which we expect to detect gravitational waves and/or neutrinos in the next years, and the achievements that will be reached from multi-messenger observations. The second part of the chapter is focused on the major facilities that are playing and that will play a crucial role in multi-messenger observational campaigns. More specifically, we provide an overview of current and next generation ground-based gravitational wave interferometers and neutrino telescopes, as well as the major X-ray and gamma-ray observatories that will be crucial for multi-messenger observations in the coming years.
Abstract: 2205.11288
Full Text: [ PostScript, PDF]
Full Text: [ PostScript, PDF]
Title:Subarcsecond view on the high-redshift blazar GB 1508+5714 by the International LOFAR Telescope
Download PDFAbstract: Studies of the most distant AGNs allow us to test our current understanding of the physics present in radio-jetted AGNs across a range of environments. The decrease in apparent luminosity with distance is the primary difficulty to overcome in the study of these distant AGNs, which requires highly sensitive instruments. Our goal is to employ new long wavelength radio data to better parametrise the broad-band SED of GB 1508+5714, a high-redshift (z=4.30) AGN. Its high redshift, high intrinsic luminosity, and classification as a blazar allow us to test emission models that consider the efficient cooling of jet electrons via inverse Compton losses in interactions with the dense CMB photon field at high redshifts. A significant detection of this effect in GB 1508+5714 may partly explain the apparent sparsity of high-redshift radio galaxies in wide-field surveys; detections of this kind are only becoming possible with the current generation of SKA precursors. We used international LOFAR telescope to image the long wavelength radio emission around the high-redshift blazar GB 1508+5714 on arcsecond scales at frequencies between 128 MHz and 160 MHz. This allowed us to compare the spatially resolved structure with higher frequency observations, and to construct spectral index maps. The LOFAR image shows a compact unresolved core and two resolved emission regions around 2 arcsec to the east and to the west of the radio core. We find structure consistent with previous VLA observations, as well as a previously unreported emission region to the east. We interpret the arcsecond-scale radio structure of GB 1508+5714 as a FR II-like radio galaxy at a small viewing angle. Our SED modelling shows that a scenario featuring significant quenching effects caused by interaction with the CMB provides a good description of the data, and notably explains the suppressed radio emission.
Abstract: 2205.11329
Full Text: [ PostScript, PDF]
Full Text: [ PostScript, PDF]
Title:Validation of high voltage power supplies for the 1-inch photomultipliers of AugerPrime, the Pierre Auger Observatory upgrade
Download PDFAbstract: In the framework of the upgrade of the Pierre Auger Observatory, a new high voltage module is being employed for the power supply of the 1-inch photomultiplier added to each water-Cherenkov detector of the surface array with the aim of increasing the dynamic range of the measurements. This module is located in a dedicated box near the electronics and comprises a low consumption DC-DC converter hosted inside an aluminum box. All the modules have undergone specific tests to verify their reliability in the extreme environmental conditions of the Argentinian pampa. In this paper, we describe the validation procedure and the facility developed to this aim. The successful results of the tests on the HVPS modules are presented and discussed.
Abstract: 2205.11410
Full Text: [ PostScript, PDF]
Full Text: [ PostScript, PDF]
Title:Searches for Neutrinos from Gamma-Ray Bursts using the IceCube Neutrino Observatory
Download PDFAbstract: Gamma-ray bursts (GRBs) are considered as promising sources of ultra-high-energy cosmic rays (UHECRs) due to their large power output. Observing a neutrino flux from GRBs would offer evidence that GRBs are hadronic accelerators of UHECRs. Previous IceCube analyses, which primarily focused on neutrinos arriving in temporal coincidence with the prompt gamma rays, found no significant neutrino excess. The four analyses presented in this paper extend the region of interest to 14 days before and after the prompt phase, including generic extended time windows and targeted precursor searches. GRBs were selected between May 2011 and October 2018 to align with the data set of candidate muon-neutrino events observed by IceCube. No evidence of correlation between neutrino events and GRBs was found in these analyses. Limits are set to constrain the contribution of the cosmic GRB population to the diffuse astrophysical neutrino flux observed by IceCube. Prompt neutrino emission from GRBs is limited to $\lesssim$1% of the observed diffuse neutrino flux, and emission on timescales up to $10^4$ s is constrained to 24% of the total diffuse flux.
Abstract: 2205.12037
Full Text: [ PostScript, PDF]
Full Text: [ PostScript, PDF]
Title:Discovery of a 584.65 Hz Burst Oscillation in the Low Mass X-Ray Binary 4U 1730$-$22
Download PDFAbstract: Type-I X-ray burst oscillations are powered by thermonuclear released on the neutron star (NS) surface in low mass X-ray binaries (LMXBs), where the burst oscillation frequencies are close to the NS spin rates. In this work, we report the detection of oscillation at 584.65 Hz during the cooling tail of a type-I X-ray bursts observed from the accreting NS LMXB 4U~1730--22 in 2022 March 20, by the \textit{ Neutron star Interior Composition Explorer} (\textit{NICER}) telescope. The oscillation signal showed a strong Leahy power, $P_{\rm m}\sim54.04$, around 584.65 Hz, which has single trial and multiple trials confidence levels of $7.05\sigma$ and $4.78\sigma$, respectively. The folded pulse profile of the oscillation in the 0.2--10 keV band showed a sinusoidal shape with the fraction amplitude rms of $(12.5\pm1.8)\%$. We found the oscillation frequency showed insignificant upward drifting, i.e., less than 0.3 Hz, during the cooling tail, similar as the behavior appearing in accreting millisecond X-ray pulsars (AMXP), and indicate the source could be an AMXP spinning at 1.71 ms.
Abstract: 2205.12146
Full Text: [ PostScript, PDF]
Full Text: [ PostScript, PDF]
Title:Gamma-ray bursts afterglow physics and the VHE domain
Download PDFAbstract: Afterglow radiation in gamma-ray bursts (GRB), extending from the radio band to GeV energies, is produced as a result of the interaction between the relativistic jet and the ambient medium. Although in general the origin of the emission is robustly identified as synchrotron radiation from the shock-accelerated electrons, many aspects remain poorly constrained, such as the role of inverse Compton emission, the particle acceleration mechanism, the properties of the environment and of the GRB jet itself. The extension of the afterglow emission into the TeV band has been discussed and theorized for years, but has eluded for a long time the observations. Recently the Cherenkov telescopes MAGIC and H.E.S.S. have unequivocally proven that afterglow radiation is produced also above $100$\,GeV, up to at least a few TeV. The accessibility of the TeV spectral window will largely improve with the upcoming facility CTA ({the} Cherenkov Telescope Array). In this review article, we first revise the current model for afterglow emission in GRBs, its limitations and open issues. Then we describe the recent detections of very high energy emission from GRBs and the origin of this radiation. Implications on the understanding of afterglow radiation and constraints on the physics of the involved processes will be deeply investigated, showing how future observations, especially {by} the CTA Observatory, are expected to give a key contribution in improving our comprehension of such elusive sources.
Abstract: 2205.12188
Full Text: [ PostScript, PDF]
Full Text: [ PostScript, PDF]
Title:Gamma/Hadron Separation with the HAWC Observatory
Download PDFAbstract: The High Altitude Water Cherenkov (HAWC) gamma-ray observatory observes atmospheric showers produced by incident gamma rays and cosmic rays with energy from 300 GeV to more than 100 TeV. A crucial phase in analyzing gamma-ray sources using ground-based gamma-ray detectors like HAWC is to identify the showers produced by gamma rays or hadrons. The HAWC observatory records roughly 25,000 events per second, with hadrons representing the vast majority ($>99.9\%$) of these events. The standard gamma/hadron separation technique in HAWC uses a simple rectangular cut involving only two parameters. This work describes the implementation of more sophisticated gamma/hadron separation techniques, via machine learning methods (boosted decision trees and neural networks), and summarizes the resulting improvements in gamma/hadron separation obtained in HAWC.
Abstract: 2205.12276
Full Text: [ PostScript, PDF]
Full Text: [ PostScript, PDF]
Title:The Gamma-Ray Emission from the Supernova Remnant RX J1713.7-3946 Interacting with Two-phase Medium
Download PDFAbstract: We study the origin of the gamma rays from the supernova remnant (SNR) RX J1713.7-3946. Using an analytical model, we calculate the distribution of cosmic rays (CRs) around the SNRs. Motivated by the results of previous studies, we assume that the SNR is interacting with two-phase interstellar medium (ISM), where dense clumps are surrounded by tenuous interclump medium. We also assume that only higher-energy protons ~>TeV) can penetrate the dense clumps. We find that pi^0-decay gamma rays produced by protons reproduce the observed gamma-ray spectrum peaked at ~TeV. On the other hand, it has recently been indicated that the observed ISM column density (N_p), the X-ray surface brightness (I_X), and the gamma-ray surface brightness (I_g) at grid points across the SNR form a plane in the three-dimensional (3D) space of (N_p, I_X, I_g). We find that the planar configuration is naturally reproduced if the ISM or the CR electron-to-proton ratio is not spherically uniform. We show that the shift of the observed data in the 3D space could be used to identify which of the quantities, the ISM density, the CR electron-to-proton ratio, or the magnetic field, varies in the azimuthal direction of the SNR.
Abstract: 2205.12950
Full Text: [ PostScript, PDF]
Full Text: [ PostScript, PDF]
Title:Searches for Connections between Dark Matter and High-Energy Neutrinos with IceCube
Download PDFAbstract: In this work, we present the results of searches for signatures of dark matter decay or annihilation into Standard Model particles, and secret neutrino interactions with dark matter. Neutrinos could be produced in the decay or annihilation of galactic or extragalactic dark matter. Additionally, if an interaction between dark matter and neutrinos exists then dark matter will interact with extragalactic neutrinos. In particular galactic dark matter will induce an anisotropy in the neutrino sky if this interaction is present. We use seven and a half years of the High-Energy Starting Event (HESE) sample data, which measures neutrinos in the energy range of approximately 60 TeV to 10 PeV, to study these phenomena. This all-sky event selection is dominated by extragalactic neutrinos. For dark matter of $\sim$ 1 PeV in mass, we constrain the velocity-averaged annihilation cross section to be smaller than $10^{-23}$cm$^3$/s for the exclusive $\mu^+\mu^-$ channel and $10^{-22}$ cm$^3$/s for the $b\bar b$ channel. For the same mass, we constrain the lifetime of dark matter to be larger than $10^{28}$ s for all channels studied, except for decaying exclusively to $b\bar b$ where it is bounded to be larger than $10^{27}$ s. Finally, we also search for evidence of astrophysical neutrinos scattering on galactic dark matter in two scenarios. For fermionic dark matter with a vector mediator, we constrain the dimensionless coupling associated with this interaction to be less than 0.1 for dark matter mass of 0.1 GeV and a mediator mass of $10^{-4}~$ GeV. In the case of scalar dark matter with a fermionic mediator, we constrain the coupling to be less than 0.1 for dark matter and mediator masses below 1 MeV.
This page created: Mon May 30 13:03:57 ACST 2022 by Adila Abdul Halim
For a printable title listing click here
For details on generating this page see the instructions. If there are problems with this page (and I expect there will be from time to time) contact Jose.
For previous lists of abstracts of interest click Previous abstracts of interest