The discovery of the serendipitous X-ray pulsar SAX J1802.7-2017 from a BeppoSAX observation of GX 9+1

We have discovered a new X-ray source, SAX J1802.7-2017, similar to 22' away from the bright X-ray source GX 9+1, during a BeppoSAX observation of this latter one on 2001 September 16-20. The count rate of SAX J1802.7 2017 is comparable to the background (similar to 0.04 c/s) during the first 50 ks of the observation, then the count rate shows a large variability increasing up to similar to 0.28 c/s. We have performed a temporal analysis finding that SAX J1802.7-2017 has a pulse period of similar to 139.61 s, a projected orbital separation a(x)sin i of 48 +/- 5 lt-s and an orbital period of 3.7(-0.2)(+0.4) days, allowing to classify the new object as an X-ray pulsar