2002ApJ...571..866U -
Astrophys. J., 571, 866-875 (2002/June-1)
ASCA view of the supernova remnant γ Cygni (G78.2+2.1): bremsstrahlung X-ray spectrum from loss-flattened electron distribution.
UCHIYAMA Y., TAKAHASHI T., AHARONIAN F.A. and MATTOX J.R.
Abstract (from CDS):
With the ASCA X-ray satellite, we perform spatial and spectral studies of the shell-type supernova remnant (SNR) γ Cygni that is associated with the brightest EGRET unidentified source 3EG J2020+4017. At energies below 3 keV, the bulk of the X-ray flux from the remnant is well described by the emission of thermal plasma with characteristic temperature kTe≃0.5-0.9 keV. In addition to this thermal emission, we found an extremely hard X-ray component from several clumps localized in the northern part of the remnant. This component, which dominates the X-ray emission from the remnant above 4 keV, is described by a power law with a photon index of Γ≃0.8-1.5. Both the absolute flux and the spectral shape of the nonthermal X-rays cannot be explained by the synchrotron or inverse-Compton mechanisms. We argue that the unusually hard X-ray spectrum can be interpreted naturally in terms of nonthermal bremsstrahlung from Coulomb-loss-flattened electron distribution in dense environs with the gas density about 10-100 cm–3. For a given spectrum of the electron population, the ratio of the bremsstrahlung X- and γ-ray fluxes depends on the position of the ``Coulomb break'' in the electron spectrum. Formally, the entire high-energy γ-ray flux detected by EGRET from γ Cygni could originate in the hard X-ray regions. However, it is more likely that the bulk of γ-rays detected by EGRET comes from the radio-bright and X-ray-dim cloud at the southeast, where the very dense gas and strong magnetic field would illuminate the cloud in the radio and γ-ray bands but suppress the bremsstrahlung X-ray emission due to the shift of the Coulomb break in the electron spectrum toward higher energies.
Abstract Copyright:
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Journal keyword(s):
Acceleration of Particles - ISM: Cosmic Rays - Radiation Mechanisms: Nonthermal - Shock Waves - ISM: Supernova Remnants
Nomenclature:
Fig.1: [UTA2002] CN (Nos C1-C3).
CDS comments:
Fig.1: R1 to R3 are regions, not objects.
Simbad objects:
13
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