X-ray line emission from supernova ejecta fragments

Abstract

We show that fast moving isolated fragments of a supernova ejecta composed of heavy elements should be sources of Kα X-ray line emission of the SN nuclear-processed products. Supersonic motion of the knots in the intercloud medium will result in a bow-shock/knot-shock structure creation. Fast nonthermal particles accelerated by Fermi mechanism in the MHD collisionless shocks diffuse through a cold metallic knot, suffering from Coulomb losses and producing the X-ray emission. We modeled the X-ray emission from a fast moving knot of mass , containing about ~10 of any metal impurities like Si, S, Ar, Ca, Fe. The accelerated electron distribution was simulated using the kinetic description of charged particles interacting with a strong MHD shock. We accounted for nonlinear effects of shock modification by the nonthermal particle pressure. The Kα line emission is most prominent for the knots propagating through dense molecular clouds. The bow shock should be a radiative wave with a prominent infrared and optical emission. In that case the X-ray line spectrum of an ejecta fragment is dominated by the low ionization states of the ions with the metal line luminosities reaching 10. High resolution XMM-Newton and Chandra observations are able to detect the K\alpha and K\beta line emission from the knots at distances up to a few kpcs. The knots propagating through tenuous interstellar matter are of much fainter surface brightness but long-lived. The line spectra with higher ionization states of the ions are expected in that case. Compact dense knots could be opaque for some X-ray lines and that is important for their abundances interpretation. The ensemble of unresolved knots of galactic supernovae can contribute substantially to the iron line emission observed from the Galactic Center region and the Galactic ridge.