Fermi Gamma-ray Space Telescope

Discovery of a Galactic Gamma-ray Binary

Robin Corbet
(L. Chomiuk, M.J. Coe, J.B. Coley, G. Dubus, P. Edwards, P. martin, V.A. McBride, J. Stevens, J. Strader, L.J. Townsend)


We are searching for gamma-ray binaries using a combination of techniques. We construct high signal-to-noise gamma-ray light curves for all sources in LAT catalogs and source lists, and search these for periodic variability that would be the sign of a binary system. We then employ a multiwavelength approach to identify counterparts, and search for periodic variability at other wavelengths. From this, we have identified a new Galactic gamma-ray binary with a period near 14 days. Similar to the two other systems discovered from this search (1FGL J1018.6-5856 and LMC P3) near-infrared spectroscopy reveals an O star counterpart. The gamma-ray flux folded on the 14 day period shows a double-peaked profile with different spectral properties for the two peaks. The X-ray and radio fluxes are also modulated on this period, but with folded profiles that exhibit single maxima close to the softer of the two gamma-ray peaks. We consider the distance limits on detection of orbitally modulated gamma-ray flux, and implications for the overall Galactic population of gamma-ray binaries.