Observational constraints on annihilation sites in 1E 1740.7-2942 and Nova Muscae

Details Observational constraints on annihilation sites in 1E 1740.7-2942 and Nova Muscae Observational constraints on annihilation sites in 1E 1740.7-2942 and Nova Muscae

1997-06-27

arxiv.org/abs/astro-ph/9706283v1

AIP Conf.Proc.410:881-885,1997

Astronomy and Astrophysics

Astrophysics

5 pages including 2 figures, latex, aipproc.sty, aipproc.cls, epsfig.sty. To be published in Proc. of 4th Compton Symp., 1997

Scientific paper

10.1063/1.54157

The region of the Galactic center contains several sources which demonstrate their activity at various wavelengths and particularly above several hundred keV. Escape of positrons from such a source or several sources into the interstellar medium, where they slow down and annihilate, can account for the 511 keV narrow line observed from this direction. 1E 1740.7-2942 object has been proposed as the most likely candidate to be responsible for this variable source of positrons. Besides, Nova Muscae shows a spectrum which is consistent with Comptonization by a thermal plasma kT<100 keV in its hard X-ray part, while a relatively narrow annihilation line observed by SIGMA on January 20-21, 1991 implies that positrons annihilate in a much colder medium. We estimate the electron number density and the size of the emitting regions suggesting that annihilation features observed by SIGMA from Nova Muscae and 1E 1740.7-2942 are due to the positron slowing down and annihilation in thermal plasma. We show that in the case of Nova Muscae the observed radiation is coming from a pair plasma stream, N(e+)~N(e-), rather than from a gas cloud. We argue that two models are probably relevant to the 1E source: annihilation in (hydrogen) plasma N(e+)<~N(e-) at rest, and annihilation in the pair plasma stream, which involves matter from the source environment.

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