RXTE Broad Band X-ray Spectrum of the Burster 1E1724-3045

Abstract

The X-ray burster 1E1724-3045 located in the globular cluster Terzan 2 is known as one of the persistent (though variable) hard X-ray sources as shown by the SIGMA observations of the Galactic Center region. 1E1724-3045 was observed with the PCA and HEXTE experiments onboard the RXTE on November 1996 for about 100 ksec. The broad band spectral capability and sensitivity of RXTE enables us to study simultaneously the X-ray (2-20 keV) and hard X-ray components (E>20 keV) of this source. During the observation, this ``Atoll'' source was in its ``Island'' state characterized by a hard Comptomized spectrum with an electron temperature kTe~29 keV, an optical depth of 2.9 (spherical geometry) and a temperature for the ``seed'' photons of 1.2 keV. Below 5 keV, there is a soft excess which we fit with a blackbody of kTbb=0.7 keV. The Comptonization temperature is significantly lower those observed for black holes candidates in their low luminosity states (kTe >~ 50 keV). Finally, our observation allows us to associate the presence of an hard tail with a low luminosity X-ray state (1-20 keV luminosity of 10^37 erg/s at 7.7 kpc).