Unidentified γ-ray Sources off the Galactic Plane as Low-Mass Microquasars? |
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Authors: | I. A. Grenier M. M. Kaufman Bernadó G. E. Romero |
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Affiliation: | (1) CEA Saclay, Université Paris VII & Service d’Astrophysique, Gif/Yvette, France;(2) Instituto Argentino de Radioastronomía, C.C. 5, Villa Elisa, Argentina |
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Abstract: | A subset of the unidentified EGRET γ-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. |
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Keywords: | X-rays binaries gamma rays observations theory gamma-ray sources unidentified microquasars |
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