The Kinematics of Kepler's Supernova Remnant as revealed by Chandra

TL;DR

This paper analyzes Chandra X-ray observations of Kepler's supernova remnant to measure its expansion, revealing variable expansion rates across different regions and implications for explosion energy and shock velocities.

Contribution

It provides detailed expansion measurements of Kepler's supernova remnant using Chandra data, highlighting regional differences and refining explosion energy estimates.

Findings

Remnant expands as r ∝ t^{0.5} on average

Northwestern part expands as r ∝ t^{0.35}

Eastern filament shows faster expansion r ∝ t^{0.7}

Abstract

I determine the expansion of the supernova remnant of SN1604 (Kepler's supernova) based on archival Chandra ACIS-S observations made in 2000 and 2006. The measurements were done in several distinct energy bands, and were made for the remnant as a whole, and for six individual sectors. The average expansion parameter indicates that the remnant expands as $r \propto t^{0.5}$, but there are significant differences in different parts of the remnant: the bright northwestern part expands as $r \propto t^{0.35}$, whereas the rest of the remnant's expansion shows an expansion $r \propto t^{0.6}$. The latter is consistent with an explosion in which the outer part of the ejecta has a negative power law slope for density ($\rho \propto v^{-n}$) of $n=7$, or with an exponential density profile($\rho \propto \exp(-v/v_e)$). The expansion parameter in the southern region, in conjunction with the shock radius, indicate a rather low value (<5E50 erg) for the explosion energy of SN1604 for a distance of 4 kpc. An higher explosion energy is consistent with the results, if the distance is larger. The filament in the eastern part of the remnant, which is dominated by X-ray synchrotron radiation seems to mark a region with a fast shock speed $r \propto t^{0.7}$, corresponding to a shock velocity of v= 4200 km/s, for a distance to SN1604 of 4 kpc. This is consistent with the idea that X-ray synchrotron emission requires shock velocities in excess of ~2000 km/s. The X-ray based expansion measurements reported are consistent with results based on optical and radio measurements, but disagree with previous X-ray measurements based on ROSAT and Einstein observations.