X-Ray Pulsar in Large Magellanic Cloud

F. D. Seward and F. R. Harnden, Jr., Harvard-Smithsonian Center for Astrophysics; and D. Helfand, Columbia Astrophysical Laboratory, report the discovery of an x-ray pulsar within or close to the Crab-like supernova remnant 0540-69.3 in the LMC. Pulsations were detected in four separate observations with the Einstein Observatory IPC. On 1979 Sept. 8.01 UT the barycentric period was 50.206102 +/- 0.000040 ms, and the period derivative measured during 1979 Apr. 11-Nov. 11 was 41.8 +/- 0.2 ns/day. Comparison with the Crab and Vela pulsars suggests that radio detection should be possible and that optical pulsations may also be observable.