THE REDDENING TOWARD CASSIOPEIA A's SUPERNOVA: CONSTRAINING THE56Ni YIELD

Abstract

We present new reddening measurements towards the young supernova remnant Cassiopeia A, using two techniques not previously applied to this object. Our observations of the near-infrared [Fe II] 1.257 micron and 1.644 micron lines show the extinction to be highly variable across the remnant, increasing towards the west and the south, consistent with previous radio and X-ray observations. While the absolute value of AV as determined by the [Fe II] lines is uncertain due to conflicting calculations and observations of their intrinsic flux ratio, parts of the remnant without previous optical measurements show comparatively higher reddening. We find AV = 6.2 +/- 0.6 from the broadband shape of the infrared synchrotron emission of a knot within 13" of the expansion center. Given this reddening, the apparent faintness of the nascent supernova, and iron mass constraints from X-ray observations, we estimate an ejected mass of 56Ni of 0.058 - 0.16 MSun. Taken with gamma-ray observations of the 44Ti decay chain, this nickel mass is broadly consistent with the solar 44Ca/56Fe ratio.