High-velocity, nonradiative shock emission in Kepler's supernova remnant

Abstract

Optical spectra of faint emission seen along the northern limb of Kepler's supernova remnant (SN 1604) show only Ha and Hß line emissions over the spectral range 4700-7000 A. The detected Ha emission consists of a broad (FWHM = 40 Â) component and a narrow, unresolved component which, together with the lack of other strong emission lines, indicates the presence of Balmer-dominated or " nonradiative " emission associated with the remnant's high-velocity shocks. This is the first report of nonradiative shock emission in this remnant. Using nonradiative shock models to interpret the width of the broad component and the flux ratio of the broad to narrow components, we estimate a shock velocity of 1670-2800 km s" 1. New CCD interference-filter images of the remnant suggest that nonradiative emission is probably present along most of the remnant's northern rim.