COMPTON-SCATTERING IN JETS - A MECHANISM FOR SIMILAR-TO-0.4 AND LESS-THAN-OR-EQUAL-TO-0.2 MEV LINE PRODUCTION

We show that gamma-ray line emission at approximately 0.4 and less tha n or similar to 0.2 MeV can be produced by Compton scattering of beame d radiation in the jets of Galactic black hole candidates. This mechan ism has the novel feature of not invoking the presence of e+-e- pairs. To produce the two lines, we employ a symmetric double-sided jet with bulk flow velocity of about 0.5c and incident beam radiation with a h ard energy spectrum. We show that the two lines can be seen at viewing -angle cosines relative to the jet ranging from 0.2 to 0.6. This compr ises 40% of the total solid angle. In addition, the line radiation is approximately 10% polarized. Depending on the bulk flow and viewing an gle, the model can produce lines at other energies as well. In particu lar, a broad feature near 1 MeV can be seen by viewing the jet close t o its axis. Our model can also accommodate single-line spectra if the beamed gamma-ray emission or the jets themselves are asymmetric.