V.H.E. Gamma Rays From Microquasars

Abstract

This thesis is concerned with the detection of very high energy (VHE) 7-rays from microquasars, a recently discovered subclass of x-ray binaries that display jets of relativistic particles. A general introduction to ground based 7-ray astronomy is presented, which discusses the production of Cherenkov radiation and how VHE 7-rays are detected via extended air showers in the atmosphere. The important processes involved in the production and absorption of 7-rays are detailed, before the design of The High Energy Stereoscopic System (H.E.S.S.) Phase I telescope array, based in Namibia, is briefly described. There follows a general section on microquasars, describing x-ray binaries and the morphological analogy between microquasars and active galactic nuclei (AGN). Some important properties of jets are detailed before the spectral states of x-ray binaries and their importance in relation to jets are discussed. A synchrotron self-Compton (SSC) model designed for AGN is reviewed in some detail and is applied to the blazar 3C 279, showing a good fit to data. This SSC model is then applied to the microquasars GRS 1915+105, V4641 Sgr and GX 339-4 using a scale-invariant method to investigate if the jets from microquasars can be considered simply as scaled down AGN jets. Conclusions are drawn from the results. Data taken with H.E.S.S. on four microquasars are presented. The techniques used to take and analyse this data are described in some detail using data taken on the Crab nebula as an example of a VHE 7-ray emitter, before the analysis results for observations of GRS 1915+105, Circinus X-1, GX 339-4 and V4641 Sgr are presented. A novel method for manufacturing aluminum mirrors suitable for use on ground based 7-ray telescopes is described in detail along with the testing techniques used. The next generation telescope, H.E.S.S. Phase II is then described briefly. The thesis concludes with a brief outline of future work to be conducted, based on the SSC model, as applied to microquasars. A proposal for observations of IGR J19140+0951, which was tentatively detected in the field of GRS 1915+105, is outlined.