ASCA Discovery of an X-Ray Pulsar in the Error Box of SGR 1900+14

We present a 2-10 keV ASCA observation of the field around the soft gamma repeater SGR 1900+14. One quiescent X-ray source was detected in this observation, and it was in the SGR error box. In 2-10 keV X-rays, its spectrum may be fitted by a power law with index -2.2, and its unabsorbed flux is 9.6 × 10-12 ergs cm-2 s-1. We also find a clear 5.16 s period. The properties of the three well-studied soft gamma repeaters are remarkably similar to one another, and they provide evidence that all of them are associated with young, strongly magnetized neutron stars in supernova remnants.