Very-high-energy gamma radiation from supernova remnants as seen with H.E.S.S

📝 Abstract

Very-high-energy (VHE, E > 100 GeV) gamma radiation has already been detected from several supernova remnants (SNRs). These objects, which are well-studied in radio, optical and X-ray wavelengths, constitute one of the most intriguing source classes in VHE astronomy. H.E.S.S., an array of four imaging atmospheric Cherenkov telescopes in Namibia, has recorded an extensive dataset of VHE gamma-ray observations covering the central region of the Milky Way, both from pointed observations as well as from the Galactic Plane Survey conducted in the inner region of the Galaxy. From radio observations, several hundred SNRs are known in the Milky Way, but until now only few of them have been identified as VHE gamma-ray emitters. Using the H.E.S.S. dataset and a large ensemble of radio SNRs localized in the inner region of the Galaxy, the standard framework that links the origin of cosmic rays to the gamma-ray visibility of SNRs can now be tested. Here we present the ensemble of investigated SNRs and discuss constraints on the parameter space used within a theoretical model of hadronic VHE gamma-ray production.

💡 Analysis

Very-high-energy (VHE, E > 100 GeV) gamma radiation has already been detected from several supernova remnants (SNRs). These objects, which are well-studied in radio, optical and X-ray wavelengths, constitute one of the most intriguing source classes in VHE astronomy. H.E.S.S., an array of four imaging atmospheric Cherenkov telescopes in Namibia, has recorded an extensive dataset of VHE gamma-ray observations covering the central region of the Milky Way, both from pointed observations as well as from the Galactic Plane Survey conducted in the inner region of the Galaxy. From radio observations, several hundred SNRs are known in the Milky Way, but until now only few of them have been identified as VHE gamma-ray emitters. Using the H.E.S.S. dataset and a large ensemble of radio SNRs localized in the inner region of the Galaxy, the standard framework that links the origin of cosmic rays to the gamma-ray visibility of SNRs can now be tested. Here we present the ensemble of investigated SNRs and discuss constraints on the parameter space used within a theoretical model of hadronic VHE gamma-ray production.

📄 Content

arXiv:1112.4976v1 [astro-ph.HE] 21 Dec 2011 32ND INTERNATIONAL COSMIC RAY CONFERENCE, BEIJING 2011 Very-high-energy gamma radiation from supernova remnants as seen with H.E.S.S. ANNE BOCHOW1, SVENJA CARRIGAN1, HENNING GAST1, VINCENT MARANDON1, MATTHIEU RENAUD2, WERNER HOFMANN1 FOR THE H.E.S.S. COLLABORATION 1Max-Planck-Institut f¨ur Kernphysik, , P.O. Box 103980, D 69029 Heidelberg, Germany 2Laboratoire de Physique Th´eorique et Astroparticules, Universit´e Montpellier 2, CNRS/IN2P3, CC 70, Place Eug`ene Bataillon, F-34095 Montpellier Cedex 5, France anne.bochow@mpi-hd.mpg.de Abstract: Very-high-energy (VHE, E > 100 GeV) γ radiation has already been detected from several supernova remnants (SNRs). These objects, which are well-studied in radio, optical and X-ray wavelengths, constitute one of the most intriguing source classes in VHE astronomy. H.E.S.S., an array of four imaging atmospheric Cherenkov telescopes in Namibia, has recorded an extensive dataset of VHE γ-ray observations covering the central region of the Milky Way, both from pointed observations as well as from the Galactic Plane Survey conducted in the inner region of the Galaxy. From radio observations, several hundred SNRs are known in the Milky Way, but until now only few of them have been identified as VHE γ-ray emitters. Using the H.E.S.S. dataset and a large ensemble of radio SNRs localized in the inner region of the Galaxy, the standard framework that links the origin of cosmic rays to the γ-ray visibility of SNRs can now be tested. Here we present the ensemble of investigated SNRs and discuss constraints on the parameter space used within a theoretical model of hadronic VHE γ-ray production. Keywords: VHE gamma radiation – SNR – Galactic 1 Introduction SNRs are widely believed to be the main sources of Galac- tic Cosmic Rays (CRs) with energies of up to 1015 eV. The amount of energy released during a supernova (SN) explo- sion, the rate of Galactic SNe and the energy density of CRs together with diffusive shock acceleration as a pos- sible acceleration mechanism make SNRs the prime can- didates for the acceleration of CRs. In radio, optical and X-ray wavelengths deep observations on SNRs have been performed and several SNRs have been discovered in the relatively young field of VHE γ-ray astronomy . With H.E.S.S. the shell-type morphology of individual SNRs such as RX J1713.7-3946 [1], SN 1006 [2], Vela Junior [3] and HESS J1731-347 [4] has been resolved. These discov- eries support the hypothesis of particle acceleration in the shell of SNRs. Using the large dataset of H.E.S.S. accumu- lated during the Galactic plane survey (GPS) [5] in recent years we study SNRs in the inner Galactic region, ranging from 275◦to 60◦in Galactic longitude and from -3◦to 3◦ in Galactic latitude. Here, the VHE γ-ray signal of known radio SNRs listed in Green’s radio SNR catalog [6] is investigated. For each SNR within the GPS region, an upper limit on the VHE γ-ray flux has been calculated and can be compared to the model predictions. In this work we test the commonly used model of the hadronic γ-ray emission expected from SNRs presented by Drury et al. [7]. They calculate the integral γ-ray flux from hadronic interactions based on intrinsic SN parameters. VHE γ rays result from the decay of neutral pi- ons generated in proton–proton interactions in the expand- ing shell of the SNR. For the first time, the high sensitivity of H.E.S.S. and the large dataset of the GPS allow us to derive upper limits that are low enough to test model pa- rameters. Using the upper limit on the VHE γ-ray flux represents a conservative test since an additional leptonic component might be present in the flux. 2 Probing the hadronic model Assuming that CRs are accelerated and VHE γ rays pro- duced in SNRs, the flux of VHE γ rays depends on ex- plosion and acceleration parameters, the properties of the ambient medium, and the distance of the SNR. Drury et al. [7] calculate the expected integral flux of VHE γ rays from SNRs generated from hadronic CR interactions above a given energy threshold E: Fγ(> E) ≈ 9 · 10−11θ  E 1 TeV −1.1  ESN 1051erg   d 1 kpc −2  n 1 cm−3  cm−2s−1, (1) ANNE BOCHOW et al.VERY-HIGH-ENERGY γ RADIATION FROM SUPERNOVA REMNANTS AS SEEN WITH H.E.S.S. where θ is the efficiency of the particle acceleration, ESN the total energy released during the supernova explosion, d the distance to the SNR and n the density of the interstellar medium surrounding the SNR. Typical values are θ = 0.1, ESN = 1051 erg and n = 1 cm−3 [7]. For this model the authors assume a power law with a spectral index of Γ = 2.1. 3 SNR sample 203 SNRs listed in Green’s radio SNR catalog are located within the H.E.S.S. GPS region. For these SNRs an up- per limit on the VHE γ-ray flux can be derived based on H.E.S.S. observations. A subsample used for the investi- gation of the hadronic model is chosen following theoret- ical considerations. The essential criterion for VHE γ-ray production is the e

This content is AI-processed based on ArXiv data.