Further studies of 1E 1740.7-2942 with ASCA

We report the ASCA results of the Great Annihilator 1E 1740.7-2942 obtained with five pointing observations in a time span of 3.5 yr. The X-ray spectr um for each period is well fitted with a single power law absorbed by a hig h column of gas. The X-ray flux changes by a factor of 2 from period to per iod, but the other spectral parameters show no significant change. The phot on index is hat with Gamma = 0.9-1.3. The column density of hydrogen N-H is similar to 1.0 x 10(23) H cm(-2) and that of iron N-Fe is similar to 10(19 ) Fe cm-2. These large column densities indicate that 1E 1740.7-2942 is nea r the Galactic center. The column density ratio leads the iron abundance to be 2 times larger than the other elements in a unit of the solar ratio. Th e equivalent width of the K alpha line from a neutral iron is less than 15 eV in 90% confidence. This indicates that the iron column density within se veral parsecs from 1E 1740.7-2942 is less than 5 x 10(17) Fe cm(-2). In add ition, the derived hydrogen column density is about one-sixth of that of gi ant molecular clouds in the line of sight. All these facts support the fact that 1E 1740.7-2942 is not in a molecular cloud, but possibly in front of it; the X-rays are not powered by accretion from a molecular cloud, but fro m a companion star like ordinary X-ray binaries.