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

We present new reddening measurements toward 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 μm and 1.644 μm lines show the extinction to be highly variable across the remnant, increasing toward the west and the south, consistent with previous radio and X-ray observations. While the absolute value of A V 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 A V = 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 56 Ni of 0.058–0.16 M ☉ . Taken with γ-ray observations of the 44 Ti decay chain, this nickel mass is broadly consistent with the solar 44 Ca/ 56 Fe ratio.