The Reddening Towards Cassiopeia A's Supernova: Constraining the 56Ni Yield

TL;DR

This study measures the variable reddening towards Cassiopeia A using novel infrared techniques, constraining the supernova's nickel-56 yield and linking it to gamma-ray observations and nucleosynthesis.

Contribution

It introduces two new methods for reddening measurement towards Cassiopeia A and estimates the nickel-56 mass based on these measurements and multi-wavelength data.

Findings

Reddening varies across the remnant, increasing towards the west and south.

Estimated AV = 6.2 +/- 0.6 from infrared synchrotron emission.

Nickel-56 mass estimated between 0.058 and 0.16 solar masses.

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.