Discovery of a transient MeV range gamma-ray source

Details Discovery of a transient MeV range gamma-ray source Discovery of a transient MeV range gamma-ray source

Apr 1995

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995apj...442..638b&link_type=abstract

Astrophysical Journal (ISSN 0004-637X), vol. 442, no. 2, Part 1, p. 638-645

Astronomy and Astrophysics

Astronomy

13

Accretion Disks, Black Holes (Astronomy), Galactic Nuclei, Gamma Ray Astronomy, Gamma Ray Bursts, Gamma Ray Spectra, Milky Way Galaxy, X Ray Astronomy, X Ray Binaries, Astrometry, Astronomical Spectroscopy, Data Reduction, Flux Density, Heao 1, Spaceborne Astronomy, Stellar Luminosity

Scientific paper

The University of California, San Diego (UCSD)/MIT hard X-ray and gamma-ray instrument on the HEAO 1 surveyed the region near the Galactic center 3 times during its lifetime in 1977-1979. During the 1977 September-October scan, a gamma-ray source was detected south of the Galactic center. The source was below the threshold sensitivity in the spring and fall of 1978. The source was detected with the medium energy phoswich scintillation counters which operated over the 80 keV-2 MeV range, had an area of 42 sq cm each, and a 17 deg FWHM aperture. The error box for the source is centered on l = 2.4 deg, b = -12.2 deg, with a 90% confidence error circle of approximately 3.5 deg radius. The flux in the 333-635 keV range was (1.89 +/- 0.29) x 10-5 photons/(sq cm s keV) and was constant within statistics during the 1 month period the source was in the field of view. The spectrum can be characterized as a Gaussian in the range 300 less than or = E less than or = 650 keV, with a FWHM of 249 +/- 51 keV centered on 461 +/- 22 keV. The flux of this broad Gaussian is (6.6 +/- 1.1) x 10-3 photons/(sq cm s). The source is tentatively identified with the 5.57 hr period low-mass X-ray-emitting binary system 1H 1822-371. Assuming this is correct, the ratio of gamma-ray to X-ray luminosity during the outburst was about 5; at a distance of 8 kpc, the gamma ray luminosity is 4 x 1037 ergs. The emission may be interpreted as a positron-pair plasma ejected from a compact object, possibly a black hole, and annihilating in a thick accretion disk surrounding the object.

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