2003ApJ...596L..63A

We report on the serendipitous discovery of a new X-ray source, SAX J1802.7-2017, ∼22' away from the bright X-ray source GX 9+1, during a BeppoSAX observation of the latter source on 2001 September 16-20. SAX J1802.7-2017 remained undetected in the first 50 ks of observation; the source count rate in the following ∼300 ks ranged between 0.04 and 0.28 counts/s, corresponding to an averaged 0.1-10 keV flux of 3.6x10^–11 ergs/cm2/s. We performed a timing analysis and found that SAX J1802.7-2017 has a pulse period of 139.612 s, a projected semimajor axis of a_xsini∼70 lt-s, an orbital period of ∼4.6 days, and a mass function f(M)∼17±5 M_☉. The new source is thus an accreting X-ray pulsar in a (possibly eclipsing) high-mass X-ray binary. The source was not detected by previous X-ray astronomy satellites, indicating that it is likely a transient system.