Modelling of the non-thermal flares in the Galactic microquasar GRS 1915+105

Abstract

The microquasars recently discovered in our Galaxy offer a unique opportunity for a deep insight into the physical processes in relativistic jets observed in different source populations. We study the temporal and spectral evolution of the radio flares detected from the relativistic ejecta in the microquasar GRS 1915+105, and propose a model that suggests that these flares are caused by synchrotron radiation of relativistic electrons suffering radiative, adiabatic and energy-dependent escape losses in fast-expanding plasmoids (radio clouds). Analytical solutions to the kinetic equation for relativistic electrons in the expanding magnetized clouds are found, and the synchrotron radiation of these electrons is calculated. Detailed comparison of the calculated radio fluxes with the ones detected from the prominent flare of GRS 1915+105 during 1994 March/April provides conclusive information on the basic parameters in the ejecta, such as the absolute values and temporal evolution of the magnetic field, the speed of expansion, the rates of continuous injection of relativistic electrons into and their energy-dependent escape from the clouds, etc. The data from radio monitoring of the pair of resolved ejecta enable unambiguous determination of the parameters of the bulk motion of the counter-ejecta and the degree of asymmetry between them, and also contain important information on the prime energy source for accelerated electrons. These data allow us, in principle, to distinguish between the scenarios of bow-shock powered and relativistic magnetized wind powered plasmoids. Assuming that the electrons in the ejecta can be accelerated up to very high energies, we also calculate the fluxes of the synchrotron and inverse Compton components of the radiation that could be expected during the flares in the broad band from radio frequencies to very high-energy γ-rays.