ROSAT HRI Detection of the 16 ms Pulsar PSR J0537-6910 Inside Supernova Remnant N157B

Based on a deep ROSAT HRI observation, we have detected a pulsed signal in the 0.1-2 keV band from PSR J0537-6910, the recently discovered pulsar associated with the supernova remnant N157B in the Large Magellanic Cloud. The measured pulse period 0.01611548182 s+/-0.02 ns, epoch MJD 50,540.5, gives a revised linear spin-down rate of 5.1271×10^-14 s s^-1, which is slightly greater than the previously derived value. The narrow pulse shape (FWHM ~ 10% duty cycle) in the ROSAT band resembles those seen in both RXTE and ASCA data (>~2 keV), but there is also marginal evidence for an interpulse. This ROSAT detection enables us to locate the pulsar at R.A.=5^h37^m47.2s, decl.=-69^deg10^'23^'' (J2000). With its uncertainty ~3", this position coincides with the centroid of a compact X-ray source. But the pulsed emission accounts for only ~10% of the source luminosity of ~2×10³⁶ ergs^-1 in the 0.1-2 keV band. These results support our previous suggestions: (1) the pulsar is moving at a high velocity (~10³ km s^-1) (2) a bow shock, formed around the pulsar, is responsible for most of the X-ray emission from the source; and (3) a collimated outflow from the bow shock region powers a pulsar wind nebula that accounts for an elongated nonthermal radio and X-ray feature to the northwest of the pulsar.