1 research outputs found
ROSAT and ASCA observations of the Crab-Like Supernova Remnant N157B in the Large Magellanic Cloud
We report the results of ROSAT and ASCA X-ray observations of the supernova
remnant N157B (or 30 Dor B, SNR 0539-69.1) in the Large Magellanic Cloud. For
comparison, we also briefly describe the results on SNR 0540-69.3, the only
confirmed Crab-like remnant in the Cloud. The X-ray emission from N157B can be
decomposed into a bright comet-shaped feature, superimposed on a diffuse
emission region of a dimension pc. The flat and nearly featureless
spectrum of the remnant is distinctly different from those of young shell-like
remnants, suggesting a predominantly Crab-like nature of N157B. Characterized
by a power law with an energy slope , the spectrum of N157B above
keV is, however, considerably steeper than that of SNR 0540-69.3,
which has a slope of . At lower energies, the spectrum of N157B
presents marginal evidence for emission lines, which if real most likely arise
in hot gas of the diffuse emission region. The hot gas has a characteristic
thermal temperature of 0.4-0.7 keV. No significant periodic signal is detected
from N157B in the period range of s. The pulsed
fraction is (99% confidence) in the keV range. We discuss
the nature of the individual X-ray components. In particular, we suggest that
the synchrotron radiation of relativistic particles from a fast-moving () pulsar explains the size, morphology, spectrum, and energetics
of the comet-shaped X-ray feature. We infer the age of the remnant as yrs. The lack of radio polarization of the remnant may be due to
Faraday dispersion by foreground \ion{H}{2} gas.Comment: To be published in The Astrophysical Journal, 21 pages, plus 11
images in the PS, GIF, or jpeg format. Postscript files of images are
available at http://www.astro.nwu.edu/astro/wqd/paper/n157b