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 asso ciated 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, give s a revised linear spin-down rate of 5.1271 x 10(-14) s s(-1), which is sli ghtly greater than the previously derived value. The narrow pulse shape (FW HM similar to 10% duty cycle) in the ROSAT band resembles those seen in bot h RXTE and ASCA data (greater than or similar to 2 keV), but there is also marginal evidence for an interpulse. This ROSAT detection enables us to loc ate the pulsar at R.A. = 5(h)37(m)47(s).2, decl. = -69 degrees 10'23" (J200 0). With its uncertainty approximate to 3", this position coincides with th e centroid of a compact X-ray source. But the pulsed emission accounts for only similar to 10% of the source luminosity of similar to 2 x 10(36) ergs( -1) in the 0.1-2 keV band. These results support our previous suggestions: (1) the pulsar is moving at a high velocity (similar to 10(3) km s(-1)); (2 ) a bow shock, formed around the pulsar, is responsible for most of the X-r ay emission from the source; and (3) a collimated outflow from the bow shoc k region powers a pulsar wind nebula that accounts for an elongated nonther mal radio and X-ray feature to the northwest of the pulsar.