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Astron. Astrophys. 361, 85-91 (2000)

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The transient X-ray source SAX J2239.3+6116 and its optical counterpart

J.J.M. in 't Zand 1, J. Halpern 2, M. Eracleous *  3, M. McCollough 4, T. Augusteijn 5, R.A. Remillard 6 and J. Heise 1

1 Space Research Organization Netherlands, Sorbonnelaan 2, 3584 CA Utrecht, The Netherlands
2 Columbia Astrophysics Laboratory, Columbia University, New York, NY 10027, USA
3 Department of Astronomy and Astrophysics, Pensylvania State University, 525 Davey Lab, University Park, PA 16802, USA
4 Universities Space Research Association, Huntsville, AL 35805, USA
5 Isaac Newton Group of Telescopes, Apartado 321, 38700 Santa Cruz de La Palma, Canary Islands, Spain
6 Center for Space Research, Massachusetts Institute of Technology, Room 37-595, Cambridge, MA 02139, USA

Received 14 April 2000 / Accepted 7 July 2000

Abstract

We have discovered with the Wide Field Cameras on board BeppoSAX the weak transient X-ray source SAX J2239.3+6116 whose position coincides with that of 4U 2238+60/3A 2237+608 and is close to that of the fast transient AT 2238+60 and the unidentified EGRET source 3EG 2227+6122. The data suggest that the source exhibits outbursts that last for a few weeks and peak to a flux of [FORMULA] erg cm-2 s-1 (2-10 keV) at maximum. During the peak the X-ray spectrum is hard with a photon index of [FORMULA]. Follow-up observations with the Narrow-Field Instruments on the same platform revealed a quiescent emission level that is 103 times less. Searches through the data archive of the All-Sky Monitor on RXTE result in the recognition of five outbursts in total from this source during 1996-1999, with a regular interval time of 262 days. Optical observations with the KPNO 2.1 m telescope provide a likely optical counterpart. It is a B0 V to B2 III star with broadened emission lines at an approximate distance of 4.4 kpc. The distance implies a 2-10 keV luminosity in the range from [FORMULA] to [FORMULA] erg s-1. The evidence suggests that SAX J2239.3+6116 is a Be X-ray binary with an orbital period of 262 days.

Key words: stars: individual: SAX J2239.3+6116, 4U 2238+60, M 2233+595, 3A 2237+608

* Visiting Astronomer, Kitt Peak National Observatory, National Optical Astronomy Observatories, which is operated by AURA, Inc., under a cooperative agreement with the National Science Foundation.

Send offprint requests to: J.J.M. in 't Zand (jeanz@sron.nl)

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© European Southern Observatory (ESO) 2000

Online publication: September 5, 2000
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