Discovery of the Galactic High-Mass Gamma-ray Binary 4FGL J1405.1-6119

R.H.D. Corbet , L. Chomiuk , M.J. Coe , J.B. Coley , G. Dubus (1) , P.G. Edwards , P. Martin (2) , V.A. Mcbride , J. Stevens , J. Strader , L.J. Townsend

1 IPAG - Institut de Planétologie et d'Astrophysique de Grenoble
2 IRAP - Institut de recherche en astrophysique et planétologie

We report the identification from multi-wavelength observations of the Fermi Large Area Telescope (LAT) source 4FGL J1405.1-6119 (= 3FGL J1405.4-6119) as a high-mass gamma-ray binary. Observations with the LAT show that gamma-ray emission from the system is modulated at a period of 13.7135 +/- 0.0019 days, with the presence of two maxima per orbit with different spectral properties. X-ray observations using the Neil Gehrels Swift Observatory X-ray Telescope (XRT) show that X-ray emission is also modulated at this period, but with a single maximum that is closer to the secondary lower-energy gamma-ray maximum. A radio source, coincident with the X-ray source, is also found from Australia Telescope Compact Array (ATCA) observations, and the radio emission is modulated on the gamma-ray period with similar phasing to the X-ray emission. A large degree of interstellar obscuration severely hampers optical observations, but a near-infrared counterpart is found. Near-infrared spectroscopy indicates an O6 III spectral classification. This is the third gamma-ray binary to be discovered with the Fermi LAT from periodic modulation of the gamma-ray emission, the other two sources also have early O star, rather than Be star, counterparts. We consider at what distances we can detect such modulated gamma-ray emission with the LAT, and examine constraints on the gamma-ray binary population of the Milky Way.

Domaines: Astrophysique [astro-ph]

R.H.D. Corbet, L. Chomiuk, M.J. Coe, J.B. Coley, G. Dubus, et al.. Discovery of the Galactic High-Mass Gamma-ray Binary 4FGL J1405.1-6119. Astrophys.J., 2019, 884 (1), pp.93. ⟨10.3847/1538-4357/ab3e32⟩. ⟨hal-02350180⟩