Is 1E 1740.7–2942 Inside the Dense Molecular Cloud? Constraints from ASCA Data

The discovery of the molecular cloud (Bally & Leventhal; Mirabel et al.) in the direction of bright and hard X-ray source 1E 1740.7-2942 raised the hypothesis that the unique properties of this object are related to the presence of a dense gas near the compact source. In particular, Bondi-Hoyle accretion onto a single black hole (Bally & Leventhal; Mirabel et al.) or onto a black hole in a binary system (Chen, Gehrels, & Leventhal) has been discussed.

We have shown below that the weakness of the 6.4 keV line in the Advanced Satellite for Cosmology and Astrophysics (ASCA) data strongly constrains averaged column density of the gas surrounding the source to the values N_H ≤ 2 × 10²² cm^-2. If most of the low-energy absorption in the direction of the source (N_H ~ 10²³ cm^-2) is due to the dense molecular cloud, then the compact source must be located behind the cloud. This would imply that Bondi-Hoyle accretion is unlikely the mechanism responsible for feeding the compact source.