Three spectral states of 1E 1740.7 - 2942 - From standard Cygnus X-1 type spectrum to the evidence of electron-positron annihilation feature

Details Three spectral states of 1E 1740.7 - 2942 - From standard Cygnus X-1 type spectrum to the evidence of electron-positron annihilation feature Three spectral states of 1E 1740.7 - 2942 - From standard Cygnus X-1 type spectrum to the evidence of electron-positron annihilation feature

Dec 1991

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1991apj...383l..49s&link_type=abstract

Astrophysical Journal, Part 2 - Letters (ISSN 0004-637X), vol. 383, Dec. 20, 1991, p. L49-L52.

Astronomy and Astrophysics

Astronomy

149

Black Holes (Astronomy), Gamma Rays, Milky Way Galaxy, Positron Annihilation, X Ray Sources, Emission Spectra, Energy Spectra, Galactic Nuclei, Spaceborne Astronomy, X Ray Astronomy

Scientific paper

The source 1E 1740.7 - 2942 is known to be the brightest hard X-ray source close to the dynamic center of the Galaxy. Three apparently different spectral states of this source were detected by the GRANAT observatory during 1990-1991 observations of the Galactic Center region. In almost all 1990 observations the source had Cyg X-1 - like spectrum with nearly constant flux. The hardest of the states (observed on October 13-14, 1990) exhibits a prominent high-energy bump on the spectrum at 300-600 keV, probably related to the annihilation processes in relatively cold electron-positron plasma. In the most recent measurements in February-March 1991 a long-term low state of 1E 1740.7 - 2942 was discovered with the source flux on the level of 15-20 percent of its 1990 value.

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