ROSAT and ASCA Observations of the Crab‐like Supernova Remnant N157B in the Large Magellanic Cloud

Abstract

We report the results of ROSAT and ASCAX-ray observations of the supernova remnant N157B (or 30 Dor B, SNR0539-69.1) in the Large Magellanic Cloud. For comparison, we alsobriefly describe the results on SNR 0540-69.3, the only confirmedCrab-like remnant in the Cloud. The X-ray emission from N157B canbe decomposed into a bright comet-shaped feature, superposed on adiffuse emission region with a dimension of ~20 pc. The flat and nearlyfeatureless spectrum of the remnant is distinctly different from thoseof young shell-like remnants, suggesting a predominantly Crab-likenature of N157B. Characterized by a power law with an energy slope of~1.5, the spectrum of N157B above ~2 keV is, however, considerablysteeper than that of SNR 0540-69.3, which has a slope of ~1.0. Atlower energies, the spectrum of N157B presents marginal evidence foremission lines, which if real most likely arise in hot gas of thediffuse emission region. The hot gas has a characteristic thermaltemperature of 0.4-0.7 keV. No significant periodic signal is detected fromN157B in the period range of 3x10-3-2000 s. The pulsed fraction is