Astronomy and Astrophysics – Astrophysics
Scientific paper
May 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006ragc.conf.....p&link_type=abstract
"International Conference "Relativistic Astrophysics, Gravitation and Cosmology" (Kiev, Ukraine)"
Astronomy and Astrophysics
Astrophysics
Snr, Thermal Emission, Nonthermal X-Rays, Nonuniform Ism
Scientific paper
In this report we consider two effects in the thermal and nonthermal spectra of supernova remnants (SNRs) which could be caused by the nonuniform ISM: i) the mimicry of the thermal X-ray spectrum of SNRs under the nonthermal one and ii) artificial broadening of the high-energy end of the nonthermal X-ray spectrum of SNRs. 1.There is possibility that the nonthermal features in the X-ray spectrum of some supernova remnants may be in fact of the thermal origin. Observed spectrum from SNRs is a superposition of ``individual'' spectra from different small volumes along the line of sight. The plasma is under different conditions in different places in SNR. The thermal X-ray spectrum of emission from a volume with high enough gradients of density and temperature may mimic under nonthermal one. This effect is studied with special attention to the case of supernova remnant evolution in the nonuniform interstellar medium like near molecular cloud. The mimicry-effect may be responsible for the nonthermal properties of X-ray spectra in those SNRs where nonthermal flux in photons with energy < 2 keV is expected to be less than thermal one in et least 2 orders of magnitude. Therefore, the effect cannot be a reason of the nonthermal features in X-ray spectra of SN 1006 and other SNRs where nonthermal flux is estimated to be of order or higher than the thermal one. 2.The observed spectrum of SNR is a superposition of many ``local'' spectra emitted by regions of SNR which are under different physical conditions. Does broadening of the high-energy end of the observed nonthermal spectrum of SNRs, like in G347.3-0.5 and SN 1006, may be an artifact of observations or is it a consequence of the microphysics involved in the acceleration process? In this note we study the influence of parameter variations in the volume and over the surface of SNR on the shape of the high-energy end of the synchrotron spectrum. It is shown that gradients of density and magnetic field strength downstream of the shock are ineffective in modification of the shape of the ``artificial'' spectrum, even if SNR evolves in the nonuniform interstellar medium. Time dependence of the maximum energy of electrons accelerated by the shock is also not able to make the observed spectrum considerably broader. The only possibility to produce broadening in the spectrum is the variation of the maximum energy of electrons over the surface of SNR. In such a case, the obliquity dependence of injection efficiency and/or magnetic field strength make also effect on the shape of the spectrum but their role is of the second order.
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