The possible evidence of the non-linear particle acceleration in Cas A from Planck data

Abstract

Arnaud et al. (2014, arXiv:1409.5746) have recently published their microwave survey Of Galactic supernova remnants by using results of observations made by Planck telescope. The high frequency radio data obtained by Planck reveal obvious concave up form of spectrum of Galactic supernova remnant (SNR) Cas A. It is expected form of spectrum if non-linear diffuse shock acceleration (DSA) process is active. The radio spectral index (the flux density Sν ∼ ν -α ) of Cas A at low and middle frequencies (< 30 GHz) has value α = 0.77. At higher frequencies (between 30 GHz and 353 GHz) this spectral index becomes flatter, α ∼ 0.6. Under assumption of the test particle DSA, as the first approximation, the corresponding compression ratio should increase from 3 (α = 0.77) to 3.5 (α = 0.6). This represents a possible observational evidence for the existence of a modified shock wave.