X-ray spectroscopic diagnosis of a wind-collimated blast wave and metal-rich ejecta from the 2006 explosion of RS Ophiuchi

Chandra HETG observations of RS Ophiuchi at day 13.9 of the 2006 outburst reveal a rich spectrum of emission lines from abundant ions formed over a wide temperature range (3 × 10⁶ to 60 × 10⁶ K) indicative of shock heating of the circumstellar medium by the expanding blast wave. Lines are asymmetric and strongly broadened (v 2400 km s^-1 at zero intensity). Using simple analytical model profiles, we show how the lines are shaped by differential absorption in the red giant wind and explosion ejecta, and that shock heating to multimillion degree temperatures appears to have occurred preferentially in the direction perpendicular to the line of sight. We conclude that the asymmetric nature of the offset 1/r ² density profile and likely equatorial circumstellar density enhancement in which the explosion occurred are responsible for both the shock collimation and broad range in plasma temperature observed. The ejecta mass deduced from X-ray absorption is more easily reconciled with the expected mass accretion rate for material enhanced in metals by up to an order of magnitude.