Search for compton-backscattered annihilation radiation from the galactic center with the OSSE

D. M. Smith*, M. Leventhal, N. Gehrels, J. Tueller, W. N. Johnson, R. L. Kinzer, J. D. Kurfess, M. S. Strickman, D. A. Grabelsky, W. R. Purcell, M. P. Ulmer, G. V. Jung

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

2 Scopus citations


An emission feature near 170 keV, interpreted as Compton-backscattered 511 keV positron-annihilation radiation has been reported twice by balloon-borne germanium spectrometers from within ∼15° of the Galactic center (Leventhal, MacCallum, & Stang 1978; Smith et al. 1993). Upper limits on this feature set by HEAO 3 (Mahoney, Ling, & Wheaton 1993) and other instruments indicate that it must be transient. We have searched data from the Oriented Scintillation Spectrometer Experiment (OSSE) on the Compton Gamma Ray Observatory (CGRO) for this feature, using daily spectral accumulations from all pointings near the Galactic center up to 1993 August, and covering most of the region viewed by the balloon instruments. We find no evidence for backscatter emission. Under the hypothesis that the source is 1E 1740.7-2942 the OSSE data set (186 days) disagrees with the balloon measurements with 99.3% confidence. The average daily 3 σ OSSE upper limit on backscatter flux from 1E 1740.7-2942 is 6.8 × 10-4 photons cm-2 s-1, compared to the 1.3 × 10-3 photons cm-2 reported by the balloon observations. We also saw no evidence in 186 days for linelike emission from the point source EXS 1737.9-2952 recently discovered by Grindlay, Covault & Manandhar (1993). This source exhibited bright emission from 83-111 keV, which has been interpreted as doubly backscattered 511 keV radiation. The average daily 3 σ upper limit from OSSE for this line is 9.8 × 10-4 photons cm-2 s-1, or ∼8% of the reported flux.

Original languageEnglish (US)
Pages (from-to)117-123
Number of pages7
JournalAstrophysical Journal
Issue number1
StatePublished - Apr 10 1995


  • Galaxy: center
  • Gamma-rays: observations

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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