Ejecta Photoionization, Clumping, and Fe Mass in SN 1006

Abstract We revisit observations of Fe absorption lines along lines of sight to background stars and quasars through the interior of SN 1006. Previous such studies of Fe II absorption lines have revealed a lower-than-expected mass of Fe for a Type Ia supernova remnant. We give a more detailed treatment of the photoionization, including the effect of UV–X-ray synchrotron radiation emitted by cosmic-ray electrons at the forward shock, and find that most of the Fe ejecta is photoionized to higher charge states, leading to higher Fe masses inferred from the Fe II absorption lines than in previous work. While the problem of lower-than-expected Fe mass is resolved, a precise determination of the Fe mass in order to understand the progenitor and the nature of the explosion depends sensitively on the time dependence of the synchrotron luminosity and, when inferred from existing X-ray observations, the degree of ejecta clumping. Plausible assumptions suggest a Chandrasekhar mass white dwarf progenitor, but other scenarios cannot so far be ruled out.