Gamma Ray binaries
Dr Brian Van Soelen, University of the Free State, South Africa
Gamma -Ray binaries are a new class of binary systems discovered in the last few decades with the progress made in gamma-ray astronomy. These sources are characterized by having spectral energy distributions that are dominated by emissions at gamma-ray energies, distinguishing them from X-ray binaries and other binaries that have been detected in gamma rays. There are currently only six known gamma-ray binary systems with a few candidate sources identified. The most often used model to explain these sources is that they consist of a non-accreting pulsar and that the non-thermal emission results from the shock which forms the pulsar and stellar winds. However the exact nature of the some of the emission is still unclear and a number of questions still remain regarding the exact location and production mechanism in the binary, in particular the production of the GeV emission detected by Fermi-LAT. the optical star in three of these sources are also Be type stars raising the further challenge of addressing the presence of the circumstellar disc influences the emission mechanisms. Here I present a review of the gamma-ray binaries, highlighting the recent achievements made as well as the challenges that still need to be addressed, especially in the era of CTA.