Ejection of the inner accretion disk in GRS 1915+105: The magnetic rubber-band effect

¹ S.N. Bose National Center for Basic Sciences, Salt Lake, 700 098, Kolkata, India
² Centre for Space Physics, 114/v/1A Raja S.C. Mullick Rd., 700047, Kolkata, India
³ Tata Institute of Fundamental Research, Homi Bhabha Road, 400 005, Mumbai (Bombay), India

Corresponding author: A. Nandi, anuj@boson.bose.res.in

Received: 19 April 2001
Accepted: 4 October 2001

Abstract

We examine theoretically the behaviour of the inner accretion disk in GRS 1915+105 when soft X-ray dips are present in the X-ray light curve. We assume the presence of a radial shock in the accretion disk, as in some of the Two Component Advective Flow (TCAF) solutions. We discuss the behaviour of the flux tubes inside a TCAF (which we name Magnetized TCAF or MTCAF model for brevity) and compare various competing forces on the flux tubes. In this MTCAF model, we find that the magnetic tension is the strongest force in a hot plasma of temperature K and as a result, magnetic flux tubes entering in this region collapse catastrophically, thereby occasionally evacuating the inner disk. We postulate that this magnetic "rubber-band" effect induced evacuated disk matter produces the blobby components of outflows and IR/radio jets. We derive the size of the post-shock region by equating the time scale of the Quasi-Periodic Oscillations to the infall time of accreting matter in the post-shock region and found the shock location to be . We calculate the transition radius r_tr, where the Keplerian disk deviates into a sub-Keplerian flow, to be . Based on the derived X-ray spectral parameters, we calculate the mass of this region to be ~10¹⁸g. We conclude that during the X-ray dips the matter in the post-shock region, which manifests itself as the thermal-Compton component in the X-ray spectrum, is ejected, along with some sub-Keplerian matter in the pre-shock region.