EDP Sciences
Free access
Volume 416, Number 2, March III 2004
Page(s) 699 - 702
Section Stellar structure and evolution
DOI http://dx.doi.org/10.1051/0004-6361:20035680

A&A 416, 699-702 (2004)
DOI: 10.1051/0004-6361:20035680

Two spectral states of the transient X-ray burster SAX J1747.0-2853

L. Natalucci1, A. Bazzano1, M. Cocchi1, P. Ubertini1, R. Cornelisse2, 3, 4, J. Heise2, 3 and J. J. M. in' t Zand2, 3

1  CNR-Istituto di Astrofisica Spaziale e Fisica Cosmica, Area Ricerca Roma 2/Tor Vergata, via del Fosso del Cavaliere 100, 00133 Roma, Italy
2  SRON National Institute for Space Research, Sorbonnelaan 2, 3584 CA Utrecht, The Netherlands
3  Astronomical Institute, Utrecht University, PO Box 80000, 3508 TA Utrecht, The Netherlands
4  Dept. of Physics and Astronomy, University of Southampton, Hampshire SO17 1BJ, UK

(Received 29 October 2003 / Accepted 4 December 2003 )

The neutron star binary SAX J1747.0-2853, located in the Galactic Center region at about 0.5 deg from Sgr A* and at a distance of ~9 kpc, has been observed in outburst four times (1998, 1999, 2000 and 2001) by BeppoSAX and RossiXTE. At the time of its discovery in 1998 the source was observed in a low/hard state, showing a hard tail with a high energy cutoff of ~70 keV. About two years later the source reappeared about one order of magnitude brighter in the X-rays (0.5-10 keV) and with a significantly steeper spectrum. As was the case for the low state, the data could be fitted by an input model based on two continuum primary components: a) a soft thermal excess, which is ~4 times more luminous than the one found in hard state; b) a non-thermal component which is compatible with either a power-law or a comptonization spectrum. The soft component is equally well described by pure blackbody or multi-color disk emission, with significantly higher temperature than observed in low state (~1.3 vs. the ~0.5 keV assuming pure blackbody). For this model, the flux of the non-thermal component below ~10 keV is a significant fraction of the total X-ray flux, i.e. greater than ~50% in the 2-10 keV band.

Key words: stars: binaries: close -- stars: individual: SAX J1747.0-2853 -- X-rays: bursts

Offprint request: L. Natalucci, lorenzo@rm.iasf.cnr.it

SIMBAD Objects

© ESO 2004