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The first detection of a gamma ray line with an energy of about 500 keV fromthe center our Galaxy dates back to the early seventies. Thanks to theastrophysical application of high spectral resolution detectors, it was soonclear that this radiation was due to the 511 keV photons generated byelectron-positron annihilation. Even though the physical process are known, theastrophysical origin of this radiation is still a mystery. The spectrometer SPIaboard the INTEGRAL gamma-ray satellite has been used to produce the firstall-sky map in light of the 511 keV annihilation, but no direct evidence for511 keV galactic compact objects has been found [...] We present the first deepIBIS 511 keV all-sky map, obtained by applying standard analysis to about 5years of data. Possible 511 keV signals are also searched over hour-day-monthtimescales. The IBIS sensitivity at 511 keV depends on the detector quantumefficiency at this energy and on the background. Both these quantities wereestimated in this work. We find no evidence of Galactic 511 keV point sources.With an exposure of 10 Ms in the center of the Galaxy, we estimate a $1.6\times 10^{-4}\,ph\,cm^{-2}\,s^{-1}$ flux 2 sigma upper limit. A similar limitis given in a wide area in the Galactic center region with similar exposures.The IBIS 511 keV flux upper limits for microquasars and supernova remnantsdetected in the hard X domain ($E > 20\, keV$) are also reported. Our resultsare consistent with a diffuse $e^{+}e^{-}$ annihilation scenario. If positronsare generated in compact objects, we expect that a significant fraction of thempropagate in the interstellar medium before there are annihilated away fromtheir birth places.

Searching for the 511 keV annihilation line from galactic compact objects with the IBIS gamma ray telescope