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F. D'Amico (CASS/UCSD and INPE/Brazil), W. Heindl, R. E. Rothschild, D. Gruber (CASS/UCSD)
We report the detection of a non-thermal hard X-ray component from Sco X--1 based upon the analysis of 20-220 keV spectra obtained with the HEXTE experiment onboard the RXTE satellite. We find that that the addition of a power-law component to a thermal bremmstrahlung model is required to achieve a good fit in some observations. Using PCA data we were able to track the movement of the source along the Z diagram, and we found that the presence of the hard X-ray tail is not confined to a specific Z position. This may imply that separate and independent emission regions are required, such as the inner accretion disk for the thermal component and the gap between the disk and the neutron star for the non-thermal flux. These observations provide firm evidence for non-thermal X--ray activity in a Z source.
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