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C.D. Dermer (NRL), M. Boettcher (Ohio U)
Very-high energy TeV \gamma-rays have recently been detected from the black-hole microquasar LS 5039 with the High Energy Stereoscopic System (HESS) ground-based \gamma-ray telescope array. A leptonic model for microquasar \gamma-ray emission is developed, using the head-on approximation for the Compton cross section and taking into account angular effects from the star's orbital motion. The spectrum of Compton-scattered accretion-disk radiation is included by approximating the accretion disk as a point source of radiation located behind the jet. Calculations are presented for power-law distributions of nonthermal electrons that are assumed to be isotropically distributed in the comoving jet frame. The results are applied to \gamma-ray observations of LS 5039. We conclude that (1) the TeV emission measured with HESS cannot result only from Compton-scattered stellar radiation (CSSR), but can be synchrotron self-Compton (SSC) emission or a combination of SSC and CSSR; (2) fitting both the HESS data and the EGRET data claimed to be associated with LS 5039 requires a very improbable leptonic model with very hard electron spectra; hadronic models face comparable difficulties. We consider various possible resolutions. One possibility is that the EGRET and HESS data are variable, and the nonsimultaneous data are not representative of the broadband spectrum. Another is that the EGRET \gamma-rays originate from another source in the error box that contains LS 5039. A likely model is that the EGRET \gamma-rays have a leptonic jet origin, and the TeV emission has a hadronic origin. The puzzle of the EGRET \gamma rays from LS 5039 will be quickly solved with GLAST.
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Bulletin of the American Astronomical Society, 37 #4
© 2005. The American Astronomical Soceity.