2005/12/31 by C. D. Dermer, Charles D. Dermer, M. Böttcher +1 · 1 citation
Physics and Astronomy · #Astrophysical Phenomena and Observations #Astrophysics and Cosmic Phenomena #Gamma-ray bursts and supernovae #astro-ph
paper · pdf · doi:10.1086/502966
published as Astrophys.J.643:1081-1097,2006 · 17 pages, 11 figures, ApJ, in press, June 1, 2006, corrected eq. 3
arxiv created 2006/05/16 · openalex publication_date 2006/06/01 · arxiv updated 2009/12/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/31
Recent High Energy Stereoscopic System (HESS) observations show that microquasars in high-mass systems are sources of very high energy γ-rays. A leptonic jet model for microquasar γ-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, we derive expressions to calculate the spectrum of γ-rays when nonthermal jet electrons Compton scatter photons of the stellar radiation field. The spectrum of Compton scattered accretion disk radiation is also derived by approximating the accretion disk as a point source of radiation located behind the jet. Numerical results are compared with simpler expressions obtained using δ-function approximations for the cross sections, from which beaming factors are derived. Calculations are presented for power-law distributions of nonthermal electrons that are assumed to be isotropically distributed in the comoving jet frame and applied to γ-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 could be synchrotron self-Compton (SSC) emission or a combination of CSSR and SSC; and (2) fitting both the HESS data and the EGRET data claimed to be associated with LS 5039 requires a very improbable leptonic model with a very hard electron energy distribution. Because the γ-rays would be variable in a leptonic jet model, the data sets are unlikely to be representative of a simultaneously measured γ-ray spectrum. We therefore attribute EGRET γ-rays primarily to CSSR emission and HESS γ-rays to SSC emission. Detection of periodic modulation of the TeV emission from LS 5039 would favor a leptonic SSC or cascade hadron origin of the emission in the inner jet, whereas stochastic variability alone would support a more extended leptonic model. The puzzle of the EGRET γ-rays from LS 5039 will be quickly solved with GLAST .