Wind Porosity Model for Gamma Ray Fluctuations in High-Mass X-ray Binary Systems
From MassiveWiki
A recent joint paper with Gustavo Romero and colleagues, submitted to the recent Potsdam Conference on Clumping in Hot-Star Winds, presents an analysis of the effect of wind clumping on gamma-ray emission in high-mass X-ray binary systems. The background model assumes a collimated jet of relativistic particles powered by accretion of stellar wind material onto a black hole, which then interacts with the wind protons to produce pions that quickly decay and emit gamma rays. The Potsdam paper applied the concept of wind porosity to derive a scaling for the relative fluctuation in this gamma ray emission due the clumped (or porous) nature of the wind. Specifically a key finding is that the relative fluctuation in gamma ray scales with the square root of the ratio of the wind porosity length h to binary separation a.
A simplifying assumption of this analysis is that the jet is so highly collimated that at any given distance it interacts with at most one clump, what we might call the thin beam limit.
I've since worked out a generalization of this analysis to account for the effects of a finite cone solid angle Ω for opening of the jet, including in the thick beam limit when the local area of of this finite jet cone becomes larger that the areal cross-section of individual wind clumps. The following describes this analysis, building directly on arguments and equations given in section 3 of the Potsdam paper.
