A Silver Anniversary Observation of the X-ray Emitting SN1978K in NGC 1313

Abstract

We describe the results of a 2003 Chandra ACIS-I observation of SN1978K. The spectrum shows little flux below 0.6 keV, in contrast to the 2002 ACIS-S observation that showed flux to 0.4 keV. Fitting the ACIS-I spectrum alone leads to two solutions depending upon the value of the column density. A joint fit using a dual thermal plasma model applied to the ACIS-I and a contemporaneous XMM spectrum, which if fit alone also leads to a two-column solution, yields a single column density fit. The fitted temperature of the joint fit for the soft component remains constant with the errors from previous Chandra, XMM, and ASCA data. The hard temperature recovers from its 2000-2002 decline and corresponds to an increase in the column density during that time. The hard (2-10 keV) light curve is confirmed to be declining. The derived number density represents a lower limit of 1e5 depending upon the adopted filling factor of the emitting volume, leading to an estimated mass cooling rate of 0.1-0.15 solar masses per year.