Gamma-Ray Spectral Characteristics of Thermal and Non-Thermal Emission from Three Black Holes

Abstract

Cygnus X-1 and the gamma-ray transients GRO J0422+32 and GRO J1719 − 24 displayed similar spectral properties when they underwent transitions between the high and low gamma-ray (30 keV to few MeV) intensity states. When these sources were in the high γ-ray intensity state (γ 2 , for Cygnus X-1), their spectra 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. When the sources were in the low-intensity state (γ 0 , for Cygnus X-1), the Comptonized spectral shape below 200 keVtypically 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. Consequently the high-and low-intensity gammaray spectra intersect, generally in the ∼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), by 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, from the database produced by EBOP, JPL's BATSE earth occultation analysis system.

Spectral properties of shocked accretion flows— a self-consistent study

“…However, unlike CT95 cases, where there was only one so-called 'pivoting' point at around a few keV, here we have an extra 'pivoting' point at a few hundred keV because of the inclusion of the synchrotron radiation. This is what is observed in black hole candidates (McConnell et al 2000(McConnell et al , 2002Ling and Wheaton 2005b;Mandal and Chakrabarti 2007).…”

Spectral fit of Cygnus X-1 in high energy— a self-consistent study

“…In the present case, however, the high energy photons are produced due to Comptonization of the non-thermal photons. We have been able to fit high energy data of several black hole candidates which were presented in Ling and Wheaton (2003, 2005a, 2005b. Details will be presented elsewhere.…”

FIRST RESULTS FROMFERMIGAMMA-RAY BURST MONITOR EARTH OCCULTATION MONITORING: OBSERVATIONS OF SOFT GAMMA-RAY SOURCES ABOVE 100 keV

“…It has been observed to emit significant emission above 100 keV including a power law tail extending out to greater than 2005b). Based on BATSE occultation analysis, Ling & Wheaton (2005b) have shown that in the high gamma-ray intensity (hard) state, the spectrum consists of a Comptonized shape below 200-300 keV with a soft (Γ > 3) power-law tail extending to at least 1 MeV. In the low-intensity (soft) state, however, the spectrum takes on a different shape: In this case, the entire spectrum from 30 keV to 1 MeV is characterized by a single power law with a harder index Γ ∼ 2 − 2.7.…”