A New Evolutionary Phase of Supernova Remnant 1987A

TL;DR

Since 1999, Chandra observations of supernova remnant 1987A reveal a significant flattening in the soft X-ray light curve, indicating the shock is interacting with a decreasing density structure, which impacts understanding of the remnant's evolution.

Contribution

This study provides the first detailed long-term X-ray light curve analysis showing a transition in the shock interaction phase of SNR 1987A.

Findings

Soft X-ray flux has flattened over the last 1.5 years.

The forward shock is likely moving beyond a density peak of the inner ring.

The flux stabilization suggests a change in the shock's environment.

Abstract

We have been monitoring the supernova remnant (SNR) 1987A with {\it Chandra} observations since 1999. Here we report on the latest change in the soft X-ray light curve of SNR 1987A. For the last $\sim$1.5 yr (since day $\sim$8000), the soft X-ray flux has significantly flattened, staying (within uncertainties) at $f_{\rm X}$ $\sim$ 5.7 $\times$ 10$^{-12}$ erg cm$^{-2}$ s$^{-1}$ (corresponding to $L_{\rm X}$ $\sim$ 3.6 $\times$ 10$^{36}$ erg s$^{-1}$) in the 0.5--2 keV band. This remarkable change in the recent soft X-ray light curve suggests that the forward shock is now interacting with a decreasing density structure, after interacting with an increasing density gradient over $\sim$10 yr prior to day $\sim$8000. Possibilities may include the case that the shock is now propagating beyond a density peak of the inner ring. We briefly discuss some possible implications on the nature of the progenitor and the future prospects of our {\it Chandra} monitoring observations.