8th HEAD Meeting, 8-11 September, 2004
Session 15 Black Holes Binaries and Intermediate Mass Black Holes
Poster, Thursday, September 9, 2004, 9:00am-10:00pm

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[15.06] Similar Gamma-Ray Spectral Characteristics of Thermal and Non-Thermal Emission Observed in Cygnus X-1, GROJ0422+32 and GROJ1719-24

J.C. Ling (JPL/Caltech), Wm. A. Wheaton (IPAC/Caltech)

BATSE-EBOP (Enhanced BATSE Occultation Package; Ling et al. 2000) gamma-ray (30 keV - 1 MeV) observations of Cygnus X-1, GROJ0422+32 and GROJ1719-24 showed that these sources displayed similar spectral characteristics when undergoing transitions between the high and low gamma-ray intensity states. The high gamma-ray state spectra (gamma-2 , for Cygnus X-1) featured two components: a Comptonized shape below 200-300 keV with a soft power-law tail (photon index > 3) that extended to ~1 MeV or beyond. For the low gamma-ray state (gamma-0, for Cygnus X-1) spectra, however, the Comptonized spectral shape below 300 keV vanished and the entire spectrum from 30 keV to ~1 MeV can be characterized by a single power law with a relatively harder photon index ~2-2.7. The high and low-intensity gamma-ray spectra therefore intersect at ~400 KeV-1 MeV range, in contrast to the spectral pivoting seen previously at lower (~10 keV) energies.

The presence of the power-law component in both the high- and low-intensity gamma-ray spectra strongly suggests that the non-thermal process is likely to be at work in both the high and the low-intensity situations. We have suggested a possible scenario (Ling & Wheaton, 2003,), combining the ADAF model of Esin et al. (1998) with a separate jet region that produces the non-thermal gamma-ray emission, and which explains the state transitions. Such a scenario will be discussed in the context of the observational evidence, summarized above. This work was carried out by the Jet Propulsion Laboratory, under the contract to the National Aeronautics and Space Administration.


Esin et al., 1998, ApJ, 505, 854.

Ling et al.,2000, ApJS , 127, 70.

Ling & Wheaton. 2003, ApJ, 584, 399.

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