Production of the large scale superluminal ejections of the microquasar GRS 1915+105 by violent magnetic reconnection

Abstract

We propose here that the large-scale superluminal ejections observed in the galactic microquasar GRS 1915+105 during radio flare events are produced by violent magnetic reconnection episodes in the corona just above the inner edge of the magnetized accretion disk that surrounds the central 10 M black hole. The process occurs when a large-scale magnetic field is established by a turbulent dynamo in the inner disk region with a ratio between the gas+radiation and the magnetic pressures 1, implying a magnetic field intensity of 7 10 8 G. During this process, substantial angular momentum is removed from the disk by the wind generated by the vertical magnetic flux therefore increasing the disk mass accretion to a value near (but below) the critical one ( 10 19 g s -1 ). Part of the magnetic energy released by reconnection heats the coronal gas (T c 5 10 8 K) that produces a steep X-ray spectrum with luminosity L X 10 39 erg s -1 , consistent with observations. The remaining magnetic energy released goes to accelerate the particles to relativistic velocities (v v A c, where v A is the Alfvn speed) in the reconnection site through first-order Fermi processes. In this context, two possible mechanisms have been examined that produce power-law electron distributions N(E) E - E , with E = 5/2, 2, and corresponding synchrotron radio power-law spectra with spectral indices which are compatible with that observed during the flares (S -0.75,-0.5 ).