Discovery of a 220 Second X‐Ray Pulsar, AX J1749.2−2725

Abstract

We report here the discovery of a faint 220 s X-ray pulsar, AX J1749.2-2725, with ASCA. In the analysis, we used a method that can detect a pulsating source in a field of view contaminated by stray light. The source was observed on four occasions between 1995 March and 1997 September. The observed source flux was ~3.0 × 10-11 ergs s-1 cm-2 (2-10 keV) in 1995 March and became an order of magnitude fainter during the 2.5 yr interval. We cannot rule out the possibility that AX J1749.2-2725 is a nearby (d ≲ 1.3 kpc) DQ Her-type white dwarf binary, while the hard X-ray spectrum and the transient behavior suggest that it is a distant (d ~ 8.5 kpc) binary system containing a neutron star.