ASCA observations of the crab-like supernova remnant 3C 58

Abstract

We present here X-ray observation of a Crab-like supernova remnant (SNR) 3C 58 with ASCA. We find that the integrated energy spectrum over the nebula is consistent with previous results, showing a power-law spectrum with the photon index of γ = 2.2-2.4, modified by interstellar absorption of about (3-4) × 1021 cm-2. The inclusion of a blackbody component, which is attributable to the central compact source, significantly improves the spectral fit. Stringent upper limits for any line emitting thin hot plasma are established. We find for the first time that the nebular spectrum is harder in the central part of the SNR, becoming softer toward the periphery, while the absorption column is uniform across the nebula. Correspondingly, the nebular size decreases with increasing photon energy, which is a steeper function of the radius than that of the Crab nebula. The results are compared with synchrotron energy-loss models, and the nature of the putative pulsar is discussed. A timing analysis was performed to search for pulsed X-ray emission from the central compact source. No significant pulsations were observed; and we present the upper limit for the pulsed fraction.