A Model for a Thin Magnetised Disc in LMC X-3
Abstract
Dynamo action in turbulent accretion discs will generate randomly oriented magnetic fields. The mean field <! !B ! !> can be assumed to be zero. We have determined the radial distribution of the r.m.s. magnetic field (i.e. the six quantities < ! !B theta 2 ! !>, < ! !B theta Br ! !>, etc.). The disc structure is determined with the help of the standard thin disc equations by allowing for the influence of the magnetic field on temperature and angular momentum. This work is an extension of that of Schramkowski et al. (1996) who considered only vertical turbulent transport of magnetic energy. We include also radial transport, energetically unimportant, but essential in that it fixes the radial distribution of the r.m.s. field. Our approach is still kinematic. It is found that a magnetic disc is thinner and hotter than its non-magnetised counterpart. If the escaping magnetic energy heats a disc corona, the radial distribution of the r.m.s. magnetic field may be inferred from the `ratio' of the thermal emission of the disc and the nonthermal emission of the corona. From the X-ray spectrum of black hole candidate LMC X-3 we confirm values in the range of 106 - 107G found by Schramkowski et al. (1996). Schramkowski G.P. et al.: 1996, A&A 315, 638.
- Publication:
-
The Hot Universe
- Pub Date:
- 1998
- Bibcode:
- 1998IAUS..188..379H