Modelling of the nonthermal flares in the galactic microquasar GRS 1915+105

Abstract

We study the temporal and spectral evolution of the radio flares detected from the relativistic ejecta in the microquasar GRS 1915+105, and develop a model which suggests that these flares are due to synchrotron radiation of relativistic electrons suffering adiabatic and radiative energy losses in fastly expanding plasmoids (radio clouds). Analytical solutions to the kinetic equation for the electrons in expanding magnetized clouds are found. Detailed comparison of the calculated radio fluxes with the ones detected from the prominent flare of GRS 1915+105 during March/April 1994 provides conclusive information on the basic parameters in the ejecta, such as the absolute values and temporal evolution of the magnetic field, speed of expansion, the rate of continuous injection of radio electrons into and their energy-dependent escape from the clouds, etc. The data of radio monitoring of the pair of resolved ejecta enable determination of parameters of the bulk motion of counter ejecta and the degree of asymmetry between them, and contain important information on the prime energy source for the accelerated electrons. Assuming that the electrons might be accelerated up to very high energies, we calculate the fluxes of synchrotron radiation up to hard X-rays/soft gamma-rays, and of the inverse Compton GeV/TeV gamma-rays expected during radio flares, and discuss the implications which could follow from either positive detection or flux upper limits of these energetic photons.