Astron. Astrophys. 357, 520-526 (2000)

BeppoSAX observations of the nearby low-mass X-ray binary and fast transient SAX J1819.3-2525

J.J.M. in 't Zand ¹, E. Kuulkers ^1,2, A. Bazzano ³, R. Cornelisse ^1,2, M. Cocchi ³, J. Heise ¹, J.M. Muller ^1,4, L. Natalucci ³, M.J.S. Smith ^1,5 and P. Ubertini <sup>3

1</sup> Space Research Organization Netherlands, Sorbonnelaan 2, 3584 CA Utrecht, the Netherlands
² Astronomical Institute, Utrecht University, P.O. Box 80000, 3508 TA Utrecht, the Netherlands
³ Istituto di Astrofisica Spaziale (CNR), Area Ricerca Roma Tor Vergata, Via del Fosso del Cavaliere, 00133 Roma, Italy
⁴ BeppoSAX Science Data Center, Nuova Telespazio, Via Corcolle 19, 00131 Roma, Italy
⁵ BeppoSAX Science Operation Center, Nuova Telespazio, Via Corcolle 19, 00131 Roma, Italy

Received 17 November 1999 / Accepted 13 January 2000

Abstract

SAX J1819.3-2525 is a nearby X-ray transient which exhibited a fast and large X-ray outburst on Sep. 15, 1999 (Smith et al. 1999). The Wide Field Cameras and the Narrow Field Instruments (NFI) on board BeppoSAX observed SAX J1819.3-2525 at various stages of its activity before that, in the spring and fall of 1999. The fluxes range between 0.012 and 0.3 Crab units (2-10 keV). The NFI observation is unique because it is the longest semi-continuous observation of SAX J1819.3-2525 so far, and it offers a study of the spectrum at a relatively high resolution of 8% full width at half maximum at 6 keV. We discuss the observations with emphasis on the X-ray spectrum. A strong Fe-K emission line was detected in SAX J1819.3-2525 with an equivalent width between 0.3 and 1 keV. The line energy is up to 6.850.02 keV and suggests the presence of highly ionized iron. We identify this as fluorescent emission from a photo-ionized plasma. The continuum spectrum is typical for a low-mass X-ray binary in which emission from an accretion disk corona plays an important role. There is no sign of an eclipse or periodic signal due to the binary orbit in this exposure, despite the fact that the twin jets seen at radio wavelengths suggest a high inclination angle.

Key words: accretion, accretion disks stars: binaries: close stars: individual: SAX J1819.3 2525, XTE J1819 254, V4641 Sgr X-rays: stars

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

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Contents

• 1. Introduction
• 2. Observations
• 3. Light curves
• 4. Spectrum of calm emission
• 5. Spectrum of flare
• 6. Discussion
• Acknowledgements
• References

© European Southern Observatory (ESO) 2000

Online publication: June 5, 2000
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