Unidentified gamma-ray Sources off the Galactic Plane as Low-Mass Microquasars?

GRENIER, I. A.; KAUFMAN BERNADÓ, M. M.; ROMERO, G. E.

ASTROPHYSICS AND SPACE SCIENCE

Springer

Lugar: Dordrecht; Año: 2005 vol. 297 p. 109 - 118

0004-640X

A subset of the unidentified EGRET ã-ray sources with no active galactic nucleus or other conspicuous counterpart appears to be concentrated at medium latitudes. Their long-term variability and their spatial distribution indicate that they are distinct from the more persistent sources associated with the nearby Gould Belt. They exhibit a large scale height of 1.3 ± 0.6 kpc above the Galactic plane. Potential counterparts for these sources include microquasars accreting from a low-mass star and spewing a continuous jet. Detailed calculations have been performed of the jet inverse Compton emission in the radiation fields from the star, the accretion disc, and a hot corona. Different jet Lorentz factors, powers, and aspect angles have been explored. The up-scattered emission from the corona predominates below 100 MeV whereas the disc and stellar contributions are preponderant at higher energies for moderate (˜15∘) and small (˜1∘) aspect angles, respectively. Yet, unlike in the high-mass, brighter versions of these systems, the external Compton emission largely fails to produce the luminosities required for 5 to 10 kpc distant EGRET sources. Synchrotron-self-Compton emission appears as a promising alternative.