VLA DATA CONSTRAINTS ON THE GALACTIC-CENTER ANNIHILATION LINE SOURCE 1E-1740.7-2942

Recent VLA observations of the annihilation line source 1E 1740.7-2942 impose rather tight restrictions on the parameters of the emitting re gion. We show that the results of radio and hard X-ray observations ar e consistent with a model in which electron-positron pairs, created in the vicinity of a black hole, become trapped in the magnetosphere sup ported by an accretion disk. The trapped relativistic pairs emit the o bserved synchrotron radiation, are cooled and then positrons annihilat e in the dense external regions of the accretion disk, producing a nar row 511 keV line. We also formulate some model-independent constraints on the magnetospheric parameters stemming from radio observations.