Using gamma-rays to probe the clumped structure of stellar winds

TL;DR

Gamma-ray observations of microquasars can reveal the clumped structure of stellar winds by analyzing variability caused by jet-wind interactions, offering a new method to probe stellar wind inhomogeneities.

Contribution

This paper demonstrates how gamma-ray variability can be used to measure the clumped structure of stellar winds in microquasars, linking gamma-ray fluctuations to wind porosity.

Findings

Gamma-ray variability scales with the square root of wind porosity to binary separation ratio.

Approximately 10% gamma-ray variation expected for moderate wind porosity.

Rapid gamma-ray variability can serve as a diagnostic for wind clumping in microquasars.

Abstract

Gamma-rays can be produced by the interaction of a relativistic jet and the matter of the stellar wind in the subclass of massive X-ray binaries known as "microquasars". The relativistic jet is ejected from the surroundings of the compact object and interacts with cold protons from the stellar wind, producing pions that then quickly decay into gamma-rays. Since the resulting gamma-ray emissivity depends on the target density, the detection of rapid variability in microquasars with GLAST and the new generation of Cherenkov imaging arrays could be used to probe the clumped structure of the stellar wind. In particular, we show here that the relative fluctuation in gamma rays may scale with the square root of the ratio of porosity length to binary separation, \sqrt{h/a}, implying for example a ca. 10 % variation in gamma ray emission for a quite moderate porosity, h/a ~ 0.01.