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Title: Fermi LAT and WMAP observations of the supernova remnant HB 21

We present the analysis of Fermi Large Area Telescope γ-ray observations of HB 21 (G89.0+4.7). We detect significant γ-ray emission associated with the remnant: the flux >100 MeV is 9.4 ± 0.8 (stat) ± 1.6 (syst) × 10{sup –11} erg cm{sup –2} s{sup –1}. HB 21 is well modeled by a uniform disk centered at l = 88.°75 ± 0.°04, b = +4.°65 ± 0.°06 with a radius of 1.°19 ± 0.°06. The γ-ray spectrum shows clear evidence of curvature, suggesting a cutoff or break in the underlying particle population at an energy of a few GeV. We complement γ-ray observations with the analysis of the WMAP 7 yr data from 23 to 93 GHz, achieving the first detection of HB 21 at these frequencies. In combination with archival radio data, the radio spectrum shows a spectral break, which helps to constrain the relativistic electron spectrum, and, in turn, parameters of simple non-thermal radiation models. In one-zone models multiwavelength data favor the origin of γ rays from nucleon-nucleon collisions. A single population of electrons cannot produce both γ rays through bremsstrahlung and radio emission through synchrotron radiation. A predominantly inverse-Compton origin of the γ-ray emission is disfavored because it requiresmore » lower interstellar densities than are inferred for HB 21. In the hadronic-dominated scenarios, accelerated nuclei contribute a total energy of ∼3 × 10{sup 49} erg, while, in a two-zone bremsstrahlung-dominated scenario, the total energy in accelerated particles is ∼1 × 10{sup 49} erg.« less
Authors:
 [1] ;  [2] ;  [3] ; ;  [4] ;  [5] ; ;  [6] ;  [7] ;  [8] ;  [9]
  1. Dipartimento di Fisica e Astronomia "G. Galilei," Università di Padova, I-35131 Padova (Italy)
  2. CRESST, University of Maryland, Baltimore County, Baltimore, MD 21250 (United States)
  3. W. W. Hansen Experimental Physics Laboratory, Kavli Institute for Particle Astrophysics and Cosmology, Department of Physics and SLAC National Accelerator Laboratory, Stanford University, Stanford, CA 94305 (United States)
  4. NASA Goddard Space Flight Center, Greenbelt, MD 20771 (United States)
  5. Laboratoire AIM, CEA-IRFU/CNRS/Université Paris Diderot, Service d'Astrophysique, CEA Saclay, F-91191 Gif sur Yvette (France)
  6. Dipartimento di Fisica "M. Merlin" dell'Università e del Politecnico di Bari, I-70126 Bari (Italy)
  7. University of Manchester, Manchester, M13 9PL (United Kingdom)
  8. Science Institute, University of Iceland, IS-107 Reykjavik (Iceland)
  9. Centre d'Études Nucléaires de Bordeaux Gradignan, IN2P3/CNRS, Université Bordeaux 1, BP120, F-33175 Gradignan Cedex (France)
Publication Date:
OSTI Identifier:
22348393
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 779; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ACCELERATION; BREMSSTRAHLUNG; COSMIC GAMMA SOURCES; COSMIC RADIATION; DENSITY; DETECTION; ELECTRON SPECTRA; ELECTRONS; EMISSION; GEV RANGE; GHZ RANGE; MEV RANGE; RELATIVISTIC RANGE; SUPERNOVA REMNANTS; SYNCHROTRON RADIATION; TELESCOPES; THERMAL RADIATION