An X‐Ray Study of the Supernova Remnant G18.95−1.1

Abstract

We present an analysis of data from both the Rontgen Satellite (ROSAT) and the Advanced Satellite for Cosmology and Astrophysics (ASCA) of the supernova remnant G18.95-1.1. We find that the X-ray emission from G18.95-1.1 is predominantly thermal, heavily absorbed with a column density around 1022 atoms cm-2, and can be best described by an nonequilibrium ionization (NEI) model with a temperature around 0.9 keV and an ionization timescale of 1.1 × 1010 cm-3 s-1. We find only marginal evidence for nonsolar abundances. Comparisons between 21 cm H I absorption data and derived parameters from our spectral analysis strongly suggest a relatively nearby remnant (a distance of about 2 kpc). Above 4 keV, we identify a small region of emission located at the tip of the central, flat-spectrum barlike feature in the radio image. We examine two possibilities for this emission region: a temperature variation within the remnant or a pulsar wind nebula (PWN). The current data do not allow us to distinguish between these possible explanations. In the scenario where this high-energy emission region corresponds to a PWN, our analysis suggests a rotational loss rate for the unseen pulsar of about 7 × 1035 ergs s-1 and a ratio Lr/LX of about 3.6 for the entire PWN, slightly above the maximum ratio (3.4 for Vela) measured in known PWNe.