The X-ray Source SLX 1732-304 in the Globular Cluster Terzan 1: The Spectral States and an X-ray Burst

Abstract

The results of ART-P/Granat observations of the X-ray burster SLX1732-304 in the globular cluster Terzan 1 are presented. The X-ray (3-20 keV) fluxes from the source differed by more than a factor of 4 during the observing sessions on September 8 ($F_{\mathrm{X}}\simeq 6.95\times 10^{-10}$ erg cm${}^{-2}$ s${}^{-1}$) and October 6, 1990 ($F_{\mathrm{X}}\simeq 1.64\times 10^{-10}$ erg cm${}^{-2}$ s${}^{-1}$). The intensity variations of SLX1732-304 were apparently accompanied by variations in its hardness: whereas the source in its high state had the spectrum with a distinct exponential cutoff typical of bright low-mass X-ray binaries, its low-state spectrum could be satisfactorily described by a simple power law with a photon index $\hat{I}\pm \simeq 1.7$. During the ART-P observation on September 8, a type I X-ray burst was detected from SLX1732-304.

17 pages, 8 figures, 3 tables. Accepted to publication in Astronomy Letters