High-cadence Dispersed Spectral Analysis of Supernova Remnant 1987A

Abstract

We present an analysis of the dispersed spectral data from 11 epochs (March 2011 to September 2018) of supernova remnant (SNR) 1987A observations performed with Chandra. These observations were performed with the High Energy Transmission Grating (HETG) as part of our ongoing Chandra monitoring campaign of SNR 1987A, whose 1st-order dispersed spectrum provides a significantly greater energy resolution than the previously-published 0th-order spectrum. Our data sets with moderate exposure times of ~50-70ks per epoch cover the time period between deep Chandra HETG observations (with individual exposures >200ks) taken in March 2011 and March 2018. These data have a much higher cadence than the widely-spaced deep high-resolution spectra, at the expense of total exposure time. While statistical uncertainties are large due to low photon count statistics in the observed 1st-order spectra, we find that spectral model parameters are generally in line with the shock wave propagating into the medium beyond the dense inner ring, as suggested by Frank et al. 2016. As the reverse shock begins ionizing the heavier elements of the supernova ejecta interior to the equatorial ring, spectral fit parameters are expected to change as the chemical makeup and physical properties of the shocked gas evolve. Based on our broadband spectral model fits, we find that abundance values appear to be constant in this time period. While our results are somewhat limited due to photon statistics, we demonstrate the utility of the dispersed HETG spectral analysis that can be performed with our regular Chandra monitoring observations of SNR 1987A.