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Astron. Astrophys. 331, L25-L28 (1998)

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Letter to the Editor

Discovery of the X-ray transient SAX J1808.4-3658, a likely low-mass X-ray binary

J.J.M. in 't Zand 1, J. Heise 1, J.M. Muller 1, 2, A. Bazzano 3, M. Cocchi 3, L. Natalucci 3 and P. Ubertini 3

1 Space Research Organization Netherlands, Sorbonnelaan 2, 3584 TA Utrecht, The Netherlands
2 BeppoSAX Science Data Center, Nuova Telespazio, Via Corcolle 19, I-00131 Roma, Italy
3 Istituto di Astrofisica Spaziale (CNR), Area Ricerca Roma Tor Vergata, Via del Fosso del Cavaliere, I-00133 Roma, Italy

Received 6 November 1997 / Accepted 20 November 1997


We report the discovery of a fairly bright transient during observations with the Wide Field Cameras on board the BeppoSAX satellite in September 1996. It was detected at a peak intensity of 0.1 Crab (2 to 10 keV) and lasted between 6 and 40 days above a detection threshold of 2 mCrab. Two very bright type I X-ray bursts were detected from this transient in the same observations. These almost certainly identify this X-ray transient as a low-mass X-ray binary with a neutron star as compact component. The double-peaked time history of both bursts at high energies suggests a peak luminosity close to the Eddington limit. Assuming this to be true implies a distance to this object of 4 kpc.

Key words: stars: neutron, SAX J1808.4-3658 – X-rays: bursts

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© European Southern Observatory (ESO) 1998

Online publication: February 16, 1998