Vortical amplification of magnetic field at inward shock of supernova remnant Cassiopeia A

TL;DR

This paper explains the 15-year X-ray flux variability in Cassiopeia A as a result of vortical magnetic field amplification at an inward shock, supported by observed flux changes and synchrotron cooling effects.

Contribution

It provides the first quantitative link between X-ray flux variability and vortical magnetic field amplification at an inward shock in a supernova remnant.

Findings

X-ray flux increased by up to 50% over 15 years.

Magnetic field growth is driven by vortical amplification at the inward shock.

Flux decrease is explained by rapid synchrotron cooling.

Abstract

We present an interpretation of the time variability of the $X$-ray flux recently reported from a multi-epoch campaign of $15$ years observations of the supernova remnant Cassiopeia A by {\it Chandra}. We show for the first time quantitatively that the $[4.2-6]$ keV non-thermal flux increase up to $50\%$ traces the growth of the magnetic field due to vortical amplification mechanism at a reflection inward shock colliding with inner overdensities. The fast synchrotron cooling as compared with shock-acceleration time scale qualitatively supports the flux decrease.