0FGL J1830.3+0617: A Fermi Blazar Near the Galactic Plane

Abstract

We present a multiwavelength study of the unidentified Fermi gamma-ray source 0FGL J1830.3+0617, which exhibits variability above 200 MeV on timescales of days to weeks. Within the Fermi 95% confidence error contour lies B1827+0617, a radio source with spectral index alpha = 0.09 between 1.4 and 4.85 GHz. The flat spectral index and flux density of 443 mJy at 4.85 GHz are consistent with the bulk of Fermi sources associated with blazars. It is also detected in the 0.3-10 keV band by Swift. Optical imaging in 2009 May identifies B1827+0617 at R ~ 16.9, and shows that it is at least 2 magnitudes brighter than on the Palomar Sky Survey plates. Contemporaneous optical spectroscopy acquired during this high state finds a weak emission line that we attribute to Mg II at redshift z = 0.75, supporting a flat spectrum radio quasar (FSRQ) classification. The variability characteristics and radio properties together indicate that 0FGL J1830.3+0617 at Galactic latitude b = 7.5 degrees is a blazar. Blazar identifications of three additional low-latitude Fermi sources, 0FGL J0643.2+0858, 0FGL J1326.6-5302, and 0FGL J1328.8-5604, are also suggested.

5 pages, 5 figures, accepted for publication in ApJ

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• Optical spectroscopic observations of gamma-ray blazar candidates II. The 2013 KPNO campaign in the Northern Hemisphere
• Optical spectroscopic observations of gamma-ray blazar candidates III. The 2013/2014 campaign in the Southern Hemisphere
• The Gamma-ray Blazar Quest: new optical spectra, state of art and future perspectives
• Optical spectroscopic observations of gamma-ray blazar candidates IV. Results of the 2014 follow-up campaign
• Refining the associations of the Fermi Large Area Telescope Source Catalogs
• Optical spectroscopic observations of low-energy counterparts of Fermi-LAT gamma-ray sources