Further Studies of 1E 1740.7-2942 with ASCA
Abstract
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 spectrum for each period is well fitted with a single power law absorbed by a high column of gas. The X-ray flux changes by a factor of 2 from period to period, but the other spectral parameters show no significant change. The photon index is flat with Γ=0.9-1.3. The column density of hydrogen NH is ~1.0×1023 H cm-2 and that of iron NFe is ~1019 Fe cm-2. These large column densities indicate that 1E 1740.7-2942 is near 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. The equivalent width of the Kα line from a neutral iron is less than 15 eV in 90% confidence. This indicates that the iron column density within several parsecs from 1E 1740.7-2942 is less than 5×1017 Fe cm-2. In addition, the derived hydrogen column density is about one-sixth of that of giant 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 from a companion star like ordinary X-ray binaries.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- July 1999
- DOI:
- 10.1086/307441
- arXiv:
- arXiv:astro-ph/9903376
- Bibcode:
- 1999ApJ...520..316S
- Keywords:
-
- ACCRETION;
- ACCRETION DISKS;
- BLACK HOLE PHYSICS;
- ISM: CLOUDS;
- STARS: INDIVIDUAL (1E 1740.7-2942);
- X-RAYS: STARS;
- Accretion;
- Accretion Disks;
- Black Hole Physics;
- ISM: Clouds;
- stars: individual (1E 1740.7-2942);
- X-Rays: Stars;
- Astrophysics
- E-Print:
- To appear in ApJ July 20, 1999 issue, Vol. 520 #1, 23 pages LaTeX files, uses aasms4.sty and psfig.sty, also available at http://www-cr.scphys.kyoto-u.ac.jp/member/sakano/work/paper/index-e.html