Discovery of a 1247 s pulsar in the Be X-ray binary SAX J2239.3+6116

¹ Astronomical Institute, Utrecht University, PO Box 80000, 3508 TA Utrecht, The Netherlands
² SRON National Institute for Space Research, Sorbonnelaan 2, 3584 CA Utrecht, The Netherlands
³ NASA Goddard Space Flight Center, Code 662, Greenbelt, MD 20771, USA
⁴ Universities Space Research Association, USA
⁵ University of Maryland, Department of Astronomy, College Park, MD, 20742, USA

Corresponding author: J. J. M. in 't Zand jeanz@sron.nl

Received: 5 October 2001
Accepted: 29 October 2001

Abstract

A search for pulsations from the Be X-ray binary SAX J2239.3+6116, through observations with the Narrow Field Instruments on BeppoSAX and the Proportional Counter Array on RXTE, yielded the clear presence of a 1247 s coherent oscillation. Given the fairly high X-ray luminosity on previous occasions (up to a few times 10³⁶ erg s^-1 in 2 to 28 keV), the oscillation must be due to the spin of a neutron star. Assuming that the 262 day recurrence time is the orbital period, SAX J2239.3+6116 has both the longest orbital period and the longest pulse period of 24 Be X-ray binaries with measured orbital periods.