Integral SPI Limits on Electron-Positron Annihilation Radiation from the Galactic Plane
Additional authors: A. Bazzano, Y.M. Butt, A. Decourchelle, A.C. Fabian, A. Goldwurm, M. Gudel, D.C. Hannikainen, A. Hornstrup, W.H.G. Lewin, K. Makishima, A. Malzac, J. Miller, A.N. Parmar, S.P. Reynolds, R.E. Rothschild, V. Schoenfelder, J.A. Tomsick, and J. Vink
Copyright for this article is held by American Astronomical Society.
The center of our Galaxy is a known strong source of electron-positron511 keV annihilation radiation.Thus far, however, there have been no reliable detections of annihilation radiation outside of the central radian of our Galaxy.One of the primary objectives of the INTEGRAL(International Gamma-Ray Astrophysics Laboratory) mission, launched in2002 October, is thedetailed study of this radiation. The Spectrometer onINTEGRAL (SPI) is ahigh-resolution, coded-aperture gamma-ray telescope with an unprecedented combinationof sensitivity, angular resolution,and energy resolution. Wereport results from thefirst 10 months of observation. During this perioda significant fraction ofthe observing time wasspent in or nearthe Galactic plane. Nopositive annihilation flux was detected outside of thecentral region ( l > 40) ofour Galaxy. In this paper we describe the observations and data analysis methods and give limits on the 511 keV flux.