Abstract:
Massive stars shape their surroundings with mass loss from winds during their lifetimes. Fast ejecta from
supernovae (SNe), from these massive stars, shock this circumstellar medium. Emission generated by this
interaction provides a window into the final stages of stellar evolution, by probing the history of mass loss from the
progenitor. Here we use Chandra and Swift X-ray observations of the type II-P/L SN 2013ej to probe the history
of mass loss from its progenitor. We model the observed X-rays as emission from both heated circumstellar matter
and SN ejecta. The circumstellar density profile probed by the SN shock reveals a history of steady mass loss
during the final 400 years. The inferred mass loss rate of 3 ´ 10 yr - - 6 1 M points back to a 14 Mprogenitor.
Soon after the explosion we find significant absorption of reverse shock emission by a cooling shell. The column
depth of this shell observed in absorption provides an independent and consistent measurement of the circumstellar
density seen in emission. We also determine the efficiency of cosmic ray acceleration from X-rays produced by
Inverse Compton scattering of optical photons by relativistic electrons. Only about 1% of the thermal energy is
used to accelerate electrons. Our X-ray observations and modeling provide stringent tests for models of massive
stellar evolution and micro-physics of shocks.
