FAST RADIATION MEDIATED SHOCKS AND SUPERNOVA SHOCK BREAKOUTS

Abstract

We present a simple analytic model for the structure of non-relativistic and\nrelativistic radiation mediated shocks. At shock velocities \\beta_s\\equiv\nv_s/c\\gtrsim 0.1, the shock transition region is far from thermal equilibrium,\nsince the transition crossing time is too short for the production of a\nblack-body photon density (by Bremsstrahlung emission). In this region,\nelectrons and photons (and positrons) are in Compton (pair) equilibrium at\ntemperatures T_s significantly exceeding the far downstream temperature, T_s\\gg\nT_d\\approx 2(\\varepsilon n_u \\hbar^3c^3)^{1/4}. T_s\\gtrsim 10 keV is reached at\nshock velocities \\beta_s\\approx 0.2. At higher velocities, \\beta_s\\gtrsim0.6,\nthe plasma is dominated in the transition region by e^\\pm pairs and 60\nkeV\\lesssim T_s \\lesssim 200 keV. We argue that the spectrum emitted during the\nbreaking out of supernova shocks from the stellar envelopes (or the surrounding\nwinds) of Blue Super Giants and Wolf-Rayet stars, which reach \\beta_s>0.1 for\nreasonable stellar parameters, may include a hard component with photon\nenergies reaching tens or even hundreds of keV. This may account for the X-ray\noutburst associated with SN2008D, and possibly for other SN-associated\noutbursts with spectra not extending beyond few 100 keV (e.g.\nXRF060218/SN2006aj).\n