Long term studies of Z sources with HEXTE/RXTE

Abstract We have analyzed the long pointed observations of the Z sources in the Rossi X-Ray Timing Explorer (RXTE) public archive to study the high energy emission in those sources. Our analysis is concentrated on the High Energy X-Ray Timing Experiment (HEXTE) waveband, since we are primarily interested in studying the hard X-ray (i.e., E >20 keV) production in those sources. We give here the preliminary results of this ongoing study. We have found no hard X-ray tails (besides ScoX-1) in our database from any of the Z sources, i.e., GX 349+2 ( −5 photons cm −2 s −1 , 3 σ , 50–150 keV), Cyg X-2 ( −5 photons cm −2 s −1 , 3 σ , 50–150 keV), GX 17+2 ( −5 photons cm −2 s −1 , 3 σ , 50–150 keV), GX5-1 ( −5 photons cm −2 s −1 , 3 σ , 50–150 keV), and GX 340+0 ( −5 photons cm −2 s −1 3 σ , 50–150 keV). From the point of view of HEXTE/ RXTE observations shown here, the production of hard X-ray tails in Z sources is a process triggered when special conditions are fulfilled. One of these conditions, as derived from our analysis, is a threshold of ∼4 × 10 36 erg s −1 for the luminosity of the source’s thermal component.