RXTE broad band X-ray spectrum of the burster 1E1724-3045 Original Research Article

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 Rossi X-ray Timing Explorer (RXTE) on November 1996 for about 100 ksec. The broad band spectral capability and sensitivity of RXTE enables to study simultaneously the X-ray (3–20 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 Comptonized spectrum with an electron temperature kTe∼ 29keV, an optical depth τ ∼ 2.9 (spherical geometry) and a temperature of the “seed” photons of kTW∼ 1.2keV. Below 5 keV, there is a soft excess which we fit with a blackbody of kTBB∼ 0.67 keV. The Comptonization temperature is significantly lower those observed for black holes candidates in their low luminosity state (kTe ≳ 50keV). 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 1.0×1037 ergs s−1 at 7.7 kpc).