This research has been supported in part by the Spanish DGICYT research grants PB 93-0030 and PB 94-1275. Part of this research was carried out by JMM at the Joint Institute for VLBI in Europe under EU contract number ERBCIPDCT950012. The National Radio Astronomy Observatory is operated by Associated Universities Inc., under cooperative agreement with the National Science Foundation of the USA. Support by the staff of the MPIfR correlator at Bonn, Germany, is warmly acknowledged. We thank R. Narayan and R. Mahadevan for providing us with flux density estimates from their advection-dominated accretion flow model and for letting us know of their results in advance.
© European Southern Observatory (ESO) 1999
Online publication: March 1, 1999