Effects of wind on radiation spectra from magnetized accretion discs

The effects of a wind on the emerging spectrum from an inefficiently radiating accretion flow in a global magnetic field are examined, based on the analytic solution obtained recently by one of the present authors. The results exhibit the steepening of the negative slope appearing in the intermediate frequency range of bremsstrahlung spectrum and the decrease in the luminosity ratio of thermal synchrotron to bremsstrahlung radiation, in accordance with the increasing wind strength. Both effects are caused by a suppressed mass accretion rate in the inner disc, caused by a mass loss in terms of wind. In order to demonstrate the reliability of this model, Sagittarius A* (Sgr A*) and the nucleus of M31, both of which have been resolved in the X-ray band by Chandra, are taken up as the best candidates for the broad-band spectral fittings. Although the observed X-ray data are reproduced for these objects by both of the inverse-Compton and the bremsstrahlung fittings, some evidence of a preference for the latter is recognized. The wind effects are clearly seen in the latter fitting case, in which we can conclude that a widely extending accretion disc is present in each nucleus, with no or only weak wind in Sgr A* and with a considerably strong wind in the nuclear region of M31. Especially in Sgr A*, the inferred mass accretion rates are much smaller than the Bondi rate, the estimate of which has become reliable because of Chandra. This fact strongly suggests that the accretion in this object does not proceed in accordance with Bondi's prediction, though its extent almost reaches the Bondi radius.