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Abstract : 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) × 10-11 erg cm-2 s-1. HB 21 is well modeled by a uniform disk centered at l = 88fdg75 ± 0fdg04, b = +4fdg65 ± 0fdg06 with a radius of 1fdg19 ± 0fdg06. 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 requires lower interstellar densities than are inferred for HB 21. In the hadronic-dominated scenarios, accelerated nuclei contribute a total energy of ~3 × 1049 erg, while, in a two-zone bremsstrahlung-dominated scenario, the total energy in accelerated particles is ~1 × 1049 erg.
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Contributor : Nathalie Martin Connect in order to contact the contributor
Submitted on : Thursday, January 23, 2014 - 11:30:24 AM
Last modification on : Wednesday, October 27, 2021 - 3:07:37 PM

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G. Pivato, J. W. Hewitt, L. Tibaldo, Fabio Acero, Jean Ballet, et al.. FERMI LAT AND WMAP OBSERVATIONS OF THE SUPERNOVA REMNANT HB 21. The Astrophysical Journal, American Astronomical Society, 2013, 779, pp.2. ⟨10.1088/0004-637X/779/2/179⟩. ⟨in2p3-00935224⟩



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