EVIDENCE FOR ELEMENTAL VARIATION IN THE EJECTA OF THE TYCHO-SUPERNOVAREMNANT

We present an X-ray study of the Tycho supernova remnant utilizing arc hival data from the high-resolution imagers (HRIs) on Einstein and ROS AT, the low-energy imaging telescopes (LEITs) on EXOSAT, and spectral data from the Broad Band X-ray Telescope (BBXRT). We have made use of the differing HRI bandpasses to construct images of Tycho in two spect ral bands, 0.7-1.8 keV and 1.8-4.5 keV. We find that the two images di ffer, with the harder image showing enhanced emission along much of th e south, west, and north periphery. There appears to be enhanced soft emission in the interior and in one particular knot of emission in the southeast. Besides continuum (which we model here as thermal bremsstr ahlung emission), we believe the hard image shows primarily the distri bution of high-ionization Si and S K-shell lines which lie in the 1.8- 2.6 keV band, while the softer image has contributions from Si as well as Fe XVII to Fe XXIV L-shell lines in the 0.7-1.4 keV band. Guided b y the results of nonequilibrium ionization modeling of the BBXRT spect ral data, we interpret the observed contrast in hard and soft X-ray em ission in terms of variations in abundance, ionization timescale, and temperature. The most likely explanation for the spectral differences are spatial variations of the relative abundances of Si, S, and Fe.