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 years. 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 densities of hydrogen N_H is $\sim$ 1.0 x 10^{23} H cm^{-2} and that of iron N_{Fe} is $\sim$ 10^{19} Fe cm^{-2}. These large column densities indicate that 1E 1740.7-2942 is near at 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 x 10^{17} Fe cm^{-2}. In addition, the derived hydrogen column density is about 1/6 of that of giant molecular clouds in the line of sight. All these facts support 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.

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

References in corpus (3)

• The Pulsar Kick Velocity Distribution
• The radio-jet X-ray binaries
• Properties Of The Hard X-ray Radiation From The Black Hole Candidates: Cygnus X-1 And 1E1740.7-2942

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• The Zoo of X-ray sources in the Galactic Center Region: Observations with BeppoSAX
• ASCA Discovery of Diffuse 6.4 keV Emission Near the Sgr C Complex: A New X-ray Reflection Nebula
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• 1E 1740.7-2942: temporal and spectral evolution from INTEGRAL and RXTE observations
• NuSTAR and INTEGRAL observations of a low/hard state of 1E1740.7-2942
• Chandra imaging spectroscopy of 1E 1740.7 - 2942
• Broadband X-ray analysis of 1E 1740.7-2942: constraints on spin, inclination and a tentative black hole mass
• Confirming the thermal Comptonization model for black hole X-ray emission in the low-hard state
• Peculiar Extended X-ray Emission around the "Radio-Loud" Black Hole Candidate 1E1740.7-2942
• Suzaku Observations of the Galactic Center Microquasar 1E 1740.7-2942
• Suzaku Observations of the Great Annihilator and the Surrounding Diffuse Emissions