Abstracts of Interest
Selected by:
Cameron Snoswell
Abstract: 1807.05230
Full Text: [ PostScript, PDF]
Full Text: [ PostScript, PDF]
Title: Studying the Milky Way Pulsar Population with Cosmic-Ray Leptons
(Submitted on 13 Jul 2018)
Abstract: Recent measurements of cosmic-ray electron and positron spectra at energies from a GeV to 5 TeV, as well as radio, X-ray and a wide range of gamma-ray observations of pulsar-wind nebulae, indicate that pulsars are significant sources of high-energy cosmic-ray electrons and positrons. Here we calculate the local cosmic-ray $e^\pm$ energy spectra from pulsars taking into account models for (a) the distribution of the pulsars spin-down properties; (b) the cosmic-ray source spectra; and (c) the physics of cosmic-ray propagation. We then use the measured cosmic-ray fluxes from AMS-02, CALET and DAMPE to constrain the space of pulsar and cosmic-ray-propagation models and in particular, local cosmic-ray diffusion and energy losses, the pulsars' energy-loss time-dependence, and the injected $e^{\pm}$ spectra. We find that the lower estimates for the local $e^{\pm}$ energy losses are inconsistent with the data. We also find that pulsar braking indexes of 2.5 or less for sources with ages more than 10 kyr are strongly disfavored. Moreover, the cosmic-ray data are consistent with a wide range of assumptions on the $e^{\pm}$ injection spectral properties and on the distribution of initial spin-down powers. Above a TeV in energy, we find that pulsars can easily explain the observed change in the $e^{+} + e^{-}$ spectral slope. These conclusions are valid as long as pulsars contribute $\gtrsim10\%$ of the observed cosmic-ray $e^\pm$ at energies $\gtrsim100$ GeV.
Abstract: 1807.05494
Full Text: [ PostScript, PDF]
Full Text: [ PostScript, PDF]
Title: Role of Cosmic Ray Streaming and Turbulent Damping in Driving Galactic Winds
(Submitted on 15 Jul 2018)
Abstract: Large-scale galactic winds driven by stellar feedback are one phenomenon that influences the dynamical and chemical evolution of a galaxy, redistributing material throughout the circumgalatic medium. Non-thermal feedback from galactic cosmic rays (CRs) -high-energy charged particles accelerated in supernovae and young stars - can impact the efficiency of wind driving. The streaming instability limits the speed at which they can escape. However, in the presence of turbulence, the streaming instability is subject to suppression that depends on the magnetization of turbulence given by its Alfv\'en Mach number. While previous simulations that relied on a simplified model of CR transport have shown that super-Alfv\'enic streaming of CRs enhances galactic winds, in the present paper we take into account a realistic model of streaming suppression. We perform three-dimensional magnetohydrodynamic simulations of a section of a galactic disk and find that turbulent damping dependent on local magnetization of turbulent interstellar medium (ISM) leads to more spatially extended gas and CR distributions compared to the earlier streaming calculations, and that scale-heights of these distributions increase for stronger turbulence. Our results indicate that the star formation rate increases with the level of turbulence in the ISM. We also find that the instantaneous wind mass loading is sensitive to local streaming physics with the mass loading dropping significantly as the strength of turbulence increases.
Abstract: 1807.05621
Full Text: [ PostScript, PDF]
Full Text: [ PostScript, PDF]
Title: Constraints on neutrino speed, weak equivalence principle violation, Lorentz invariance violation, and dual lensing from the first high-energy astrophysical neutrino source TXS 0506+056
(Submitted on 15 Jul 2018)
Abstract: We derive some of the most stringent constraints on neutrino speed, weak equivalence principle violation, Lorentz invariance violation, and dual lensing from the first high-energy astrophysical neutrino source: TXS 0506+056. Observation of neutrino (IceCube-170922A) and photons in a similar time frame and from the same direction is used to derive these limits. All of these constraints are stronger than those obtained from the observation of SN 1987A. We describe ways in which these constraints can be further improved by orders of magnitude.
Abstract: 1807.06079
Full Text: [ PostScript, PDF]
Full Text: [ PostScript, PDF]
Title: Gamma-ray emission of hot astrophysical plasma
(Submitted on 16 Jul 2018)
Abstract: Very hot plasmas with ion temperature exceeding $10^{10}$~K can be formed in certain astrophysical environments. The distinct radiation signature of such plasmas is the $\gamma$-ray emission dominated by the prompt de-excitation nuclear lines and $\pi^0$-decay $\gamma$-rays. Using a large nuclear reaction network, we compute the time evolution of the chemical composition of such hot plasmas and their $\gamma$-ray line emissivity. At higher energies, we provide simple but accurate analytical presentations for the $\pi^0$-meson production rate and the corresponding $\pi^0\to2\gamma$ emissivity derived for the Maxwellian distribution of protons. We discuss the impact of the possible deviation of the high energy tail of the particle distribution function from the "nominal" Maxwellian distribution on the plasma $\gamma$-ray emissivity.
Abstract: 1807.06504
Full Text: [ PostScript, PDF]
Full Text: [ PostScript, PDF]
Title: Multimessenger Tests of Einstein's Weak Equivalence Principle and Lorentz Invariance with a High-energy Neutrino from a Flaring Blazar
(Submitted on 17 Jul 2018)
Abstract: The detection of the high-energy ($\sim290$ TeV) neutrino coincident with the flaring blazar TXS 0506+056, the first and only $3\sigma$ neutrino-source association to date, provides new, multimessenger tests of the weak equivalence principle (WEP) and Lorentz invariance. Assuming that the flight time difference between the TeV neutrino and gamma-ray photons from the blazar flare is mainly caused by the gravitational potential of the Laniakea supercluster of galaxies, we show that the deviation from the WEP for neutrinos and photons is conservatively constrained to be an accuracy of $10^{-6}-10^{-7}$, which is 3--4 orders of magnitude better than previous results placed by MeV neutrinos from supernova 1987A. In addition, we demonstrate that the association of the TeV neutrino with the blazar flare sets limits on the energy scale of quantum gravity for both linear and quadratic violations of Lorentz invariance (LIV) to $E_{\rm QG, 1}>3.2\times10^{15}-3.7\times10^{16}$ GeV and $E_{\rm QG, 2}>4.0\times10^{10}-1.4\times10^{11}$ GeV. These improve previous limits on both linear and quadratic LIV in neutrino propagation by 5--7 orders of magnitude.
Abstract: 1807.06595
Full Text: [ PostScript, PDF]
Full Text: [ PostScript, PDF]
Title: Evidence for Cosmic-Ray Escape in the Small Magellanic Cloud using Fermi Gamma-rays
(Submitted on 17 Jul 2018)
Abstract: Galaxy formation simulations demonstrate that cosmic-ray (CR) feedback may be important in the launching of galactic-scale winds. CR protons dominate the bulk of the CR population, yet most observational constraints of CR feedback come from synchrotron emission of CR electrons. In this paper, we present an analysis of 105 months of Fermi Gamma-ray Space Telescope observations of the Small Magellanic Cloud (SMC), with the aim of exploring CR feedback and transport in an external galaxy. We produce maps of the 2-300 GeV emission and detect statistically significant, extended emission along the Bar and the Wing, where active star formation is occurring. Gamma-ray emission is not detected above 13 GeV, and we set stringent upper-limits on the flux above this energy. We find the best fit to the gamma-ray spectrum is a single-component model with a power-law of index $\Gamma=-2.11\pm0.06\pm0.06$ and an exponential cutoff energy of $E_{\rm c} =13.1\pm5.1\pm1.6$ GeV. We assess the relative contribution of pulsars and CRs to the emission, and we find that pulsars may produce up to 14$^{+4}_{-2}$% of the flux above 100 MeV. Thus, we attribute most of the gamma-ray emission (based on its spectrum and morphology) to CR interactions with the ISM. We show that the gamma-ray emissivity of the SMC is five times smaller than that of the Milky Way and that the SMC is far below the calorimetric limit, where all CR protons experience pion losses. We interpret these findings as evidence that CRs are escaping the SMC via advection and diffusion.
Abstract: 1807.06798
Full Text: [ PostScript, PDF]
Full Text: [ PostScript, PDF]
Title: Two blobs in a jet model for the gamma-ray emission in radio galaxies
(Submitted on 18 Jul 2018)
Abstract: In the unified scheme FR I type radio galaxies are identified with the blazar type active galaxies which jets are aligned at large angles to the line of sight. A few radio galaxies of this type have been discovered to emit GeV-TeV gamma-rays. We consider a scenario which naturally explains the very high energy gamma-ray emission at large angles to the jet axis. It is proposed that two emission regions are present in the jet at this same moment. The inner region (blob I), moves with the large Lorentz factor, producing radiation strongly collimated along the jet axis, as observed in BL Lac type blazars. On the other hand, the outer region (blob II), which moves with the mild Lorentz factor, contains isotropically distributed relativistic electrons in the blob reference frame. These electrons up-scatter mono-directional soft radiation from the blob I preferentially in the direction opposite to the jet motion. Therefore, gamma-rays, produced in the blob II, can be emitted at a relatively large angles to the jet axis in the observer's reference frame. We analyze the basic emission features of such external blob radiation model. The example modeling of the emission from the FR I type radio galaxy, NGC 1275, is presented.
Abstract: 1807.07160
Full Text: [ PostScript, PDF]
Full Text: [ PostScript, PDF]
Title: Possible GeV counterpart at the ground level associated with Fermi LAT gamma-ray bursts
(Submitted on 18 Jul 2018)
Abstract: From June 2014 to February 2017, the Fermi LAT detected 46 gamma-ray bursts (GRBs) with photon energies above 20 MeV, and the trigger coordinates of seven of them were within the FoV of New-Tupi detector located in the central region of the South Atlantic Anomaly (SAA). We show in this paper that two of these seven GRBs have a probable GeV counterpart observed at ground level by New-Tupi detector. The first is GRB 160609A, a short duration GRB with a bright emission of photons over a broad energy range extending up to GeV energies. The second is GRB 160625B, a very long duration GRB, for which the Fermi LAT detected more than 300 photons with energies above 100 MeV in the $\sim$ 1 ks interval after the GBM trigger. In the first case, the signal at New-Tupi has a nominal significance of $3.5\sigma$ in the counting rate time profiles, within the T90($=5.6$ s) duration on Fermi GBM. However, the effective significance is only $3.0\sigma$. In the second case, New-Tupi detector registered at least two excess (peaks) with a nominal statistical significance of $4.8\sigma$ and $5.0\sigma$ at 438 s and 558 s after the trigger. The first is within the $T90(=460$ s) on Fermi GBM. Even so, the effective significance is only $\sim 2.0\sigma$. In addition, from a Monte Carlo analysis, we show that the expected signal-to-noise ratio is compatible with the observation of GRB 160709A, only if the differential index of the GRB energy spectrum be equal or higher than -2.2 (a non-steep spectrum).
Abstract: 1807.07462
Full Text: [ PostScript, PDF]
Full Text: [ PostScript, PDF]
Title: Mid-infrared variability of the neutrino source blazar TXS 0506$+$056
(Submitted on 19 Jul 2018)
Abstract: The IceCube instrument detected a high-energy cosmic neutrino event on 2017 September 22 (IceCube_170922A, IceCube Collaboration 2018), which the electromagnetic follow-up campaigns associated with the flaring $\gamma$-ray blazar TXS 0506$+$056 (e.g., Padovani et al., 2018). We investigated the mid-infrared variability of the source by using the available single exposure data of the WISE satellite at $3.4$ and $4.6\mu$m. TXS 0506$+$056 experienced a $\sim 30$% brightening in both of these bands a few days prior to the neutrino event. Additional intraday infrared variability can be detected in 2010. Similar behaviour seen previously in $\gamma$-ray bright radio-loud AGN has been explained by their jet emission (e.g., Jiang et al. 2012).
Abstract: 1807.07938
Full Text: [ PostScript, PDF]
Full Text: [ PostScript, PDF]
Title: Sterile Neutrino Dark Matter
(Submitted on 20 Jul 2018)
Abstract: We review sterile neutrinos as possible Dark Matter candidates. After a short summary on the role of neutrinos in cosmology and particle physics, we give a comprehensive overview of the current status of the research on sterile neutrino Dark Matter. First we discuss the motivation and limits obtained through astrophysical observations. Second, we review different mechanisms of how sterile neutrino Dark Matter could have been produced in the early universe. Finally, we outline a selection of future laboratory searches for keV-scale sterile neutrinos, highlighting their experimental challenges and discovery potential.
Abstract: 1807.07944
Full Text: [ PostScript, PDF]
Full Text: [ PostScript, PDF]
Title: The Maxwell's demon of star clusters
(Submitted on 20 Jul 2018)
Abstract: Stellar binaries are the most important energy reservoir of star clusters. Via three-body encounters, binaries can reverse the core collapse and prevent a star cluster from reaching equipartition. Moreover, binaries are essential for the formation of stellar exotica, such as blue straggler stars, intermediate-mass black holes and massive ($\gtrsim{}30$ M$_\odot$) black hole binaries.
Abstract: 1807.08010
Full Text: [ PostScript, PDF]
Full Text: [ PostScript, PDF]
Title: Measurement of the Iron Spectrum in Cosmic Rays by VERITAS
(Submitted on 20 Jul 2018)
Abstract: We present a new measurement of the energy spectrum of iron nuclei in cosmic rays from 20 to 500 TeV. The measurement makes use of a template-based analysis method, which, for the first time, is applied to the energy reconstruction of iron-induced air showers recorded by the VERITAS array of imaging atmospheric Cherenkov telescopes. The event selection makes use of the direct Cherenkov light which is emitted by charged particles before the first interaction, as well as other parameters related to the shape of the recorded air shower images. The measured spectrum is well described by a power law $\frac{\mathrm{d} F}{\mathrm{d} E}=f_0\cdot \left(\frac{E}{E_0}\right)^{-\gamma}$ over the full energy range, with $\gamma = 2.82 \pm 0.30 \mathrm{(stat.)} ^{+0.24}_{-0.27} \mathrm{(syst.)}$ and $f_0 = \left( 4.82 \pm 0.98 \mathrm{(stat.)}^{+2.12}_{-2.70} \mathrm{(syst.)} \right)\cdot 10^{-7}$m$^{-2}$s$^{-1}$sr$^{-1}$TeV$^{-1}$ at $E_0=50$TeV, with no indication of a cutoff or spectral break. The measured differential flux is compatible with previous results, with improved statistical uncertainty at the highest energies.
Abstract: 1807.08231
Full Text: [ PostScript, PDF]
Full Text: [ PostScript, PDF]
Title: Computational Challenges and Opportunities of Simulating Cosmic Ray Showers at Global Scale
(Submitted on 22 Jul 2018)
Abstract: Galactic cosmic rays are the high-energy particles that stream into our solar system from distant corners of our Galaxy and some low energy particles are from the Sun which are associated with solar flares. The Earth atmosphere serves as an ideal detector for the high energy cosmic rays which interact with the air molecule nuclei causing propagation of extensive air showers. In recent years, there are growing interests in the applications of the cosmic ray measurements which range from the space/earth weather monitoring, homeland security based on the cosmic ray muon tomography, radiation effects on health via air travel, etc. A simulation program (based on the GEANT4 software package developed at CERN) has been developed at Georgia State University for studying the cosmic ray showers in atmosphere. The results of this simulation study will provide unprecedented knowledge of the geo-position-dependent cosmic ray shower profiles and significantly enhance the applicability of the cosmic ray applications. In the paper, we present the computational challenges and the opportunities for carrying out the cosmic ray shower simulations at the global scale using various computing resources including XSEDE.
Abstract: 1807.08726
Full Text: [ PostScript, PDF]
Full Text: [ PostScript, PDF]
Title: Universal Afterglow Of Supernova-Less Gamma Ray Bursts
(Submitted on 23 Jul 2018)
Abstract: The well-sampled afterglows of gamma ray bursts (GRBs) not associated with a supernova (SN) explosion, can be scaled down to a simple dimensionless universal formula, which describes well their temporal behavior. Such SN-less GRBs include short hard bursts (SHBs) and long SN-less GRBs. The universal temporal behavior of their afterglows is that expected from a pulsar wind nebula powered by the rotational energy loss of the newly born milli second pulsar.
Abstract: 1807.08734
Full Text: [ PostScript, PDF]
Full Text: [ PostScript, PDF]
Title: Origins of Extragalactic Cosmic Ray Nuclei by Contracting Alignment Patterns induced in the Galactic Magnetic Field
(Submitted on 23 Jul 2018)
Abstract: We present a novel approach to search for origins of ultra-high energy cosmic rays. These particles are likely nuclei that initiate extensive air showers in the Earth's atmosphere. In large-area observatories, the particle arrival directions are measured together with their energies and the atmospheric depth at which their showers maximize. The depths provide rough measures of the nuclear charges. In a simultaneous fit to all observed cosmic rays we use the galactic magnetic field as a mass spectrometer and adapt the nuclear charges such that their extragalactic arrival directions are concentrated in as few directions as possible. Using different simulated examples we show that, with the measurements on Earth, reconstruction of extragalactic source directions is possible. In particular, we show in an astrophysical scenario that source directions can be reconstructed even within a substantial isotropic background.
This page created: Tue Jul 24 11:03:11 ACST 2018 by Cameron Snoswell
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