The great annihilator 1E 1740.7-2942: Molecular cloud connection and coronal structure

Using (12)CO and (13)CO observations, column density maps of the molecular cloud in the direction of 1E 1740.7-2942 are presented. Hydrogen column densities of the cloud vary between N(sub H) = 3.5 x 10(exp 22)/cu cm and 11 x 10(exp 22)/cu cm, depending on the method employed. From this, it is concluded that, despite the weakness of the iron fluorescent 6.4 keV line, the source may lie inside the cloud, or at least close to its edge. The combined spectra from the Advanced Satellite for Cosmology and Astrophysics (ASCA) and the burst and transient source experiment (BATSE) can be modeled with a two phase accretion disk corona model, where the hot region is detached from the cold disk. Geometrically, the hot phase can be interpreted as a number of active regions above the disk, or as a spherical hot cloud about the central object.