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

摘要

We examine theoretically the behaviour of the inner accretion disk in GRS1915+105 when soft X-ray dips are present in the X-ray light curve. We assumethe presence of a radial shock in the accretion disk, as in some of the TwoComponent Advective Flow (TCAF) solutions. We discuss the behaviour of the fluxtubes 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, wefind that the magnetic tension is the strongest force in a hot plasma oftemperature $\gsim 10^{10}$K and as a result, magnetic flux tubes entering inthis region collapse catastrophically, thereby occasionally evacuating theinner disk. We postulate that this magnetic `rubber-band' effect inducedevacuated disk matter produces the blobby components of outflows and IR/radiojets. We derive the size of the post-shock region by equating the time scale ofthe Quasi-Periodic Oscillations to the infall time of accreting matter in thepost-shock region and found the shock location to be $\sim 45-66 r_g$. Wecalculate the transition radius $r_{tr}$, where the Keplerian disk deviatesinto a sub-Keplerian flow, to be $\sim 320r_g$. Based on the derived X-rayspectral parameters, we calculate the mass of this region to be $\sim10^{18}$g.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.