WU, M (reprint author), CHINESE ACAD SCI,INST HIGH ENERGY PHYS,HIGH ENERGY ASTROPHYS LAB,POB 9183,BEIJING,PEOPLES R CHINA.
Positron annihilation radiation from the direction of the Galactic center (GC) has been observed for over two decades. A detailed analysis of the observations has shown that the GC annihilation source consists of both a ''steady state'' diffuse component plus one or more highly variable point sources (see, e.g., Lingenfelter & Ramaty 1989 and references therein). As to the annihilation radiation directly from binary systems, discussions are few to date. In this paper we make a detailed investigation of the electron-positron annihilation process around X-ray binary systems, typically the Cygnus X-3 system, by a Monte Carlo calculation. Our results show that there exists a narrow 511 keV annihilation line emitted from some kind of X-ray binary systems, for example, from an accreting neutron star X-ray source which contains an optically thick accretion disk corona. The significance and width of radiation lines depend on the corona electron density and the size, status, and temperature distribution of the X-ray halo around the binary system. For a typical accreting neutron star X-ray binary source, the annihilation radiation is detectable by the CGRO/OSSE detector. Since some researchers believe that the point source candidates of the GC annihilation radiation may be 1E 1740.7-2942 and GX 1+4 and/or others, which would be X-ray binaries, this work may give a hint for understanding the emission mechanism of the GC annihilation radiation.