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

¹ Universidade de São Paulo, IAG, Rua do Matão 1226, Cidade Universitária, São Paulo 05508-900, Brazil e-mail: dalpino@astro.iag.usp.br
² Department of Astronomy, University of Wisconsin, Madison, USA e-mail: lazarian@astro.wisc.edu

Received: 21 December 2004
Accepted: 13 June 2005

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 ~ 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 , implying a magnetic field intensity of ~ 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 ( g s^-1). Part of the magnetic energy released by reconnection heats the coronal gas ( K) that produces a steep X-ray spectrum with luminosity erg s^{- 1}, consistent with observations. The remaining magnetic energy released goes to accelerate the particles to relativistic velocities (, where v_A is the Alfvén 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 , with , and corresponding synchrotron radio power-law spectra with spectral indices which are compatible with that observed during the flares ().