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

TL;DR

This study identifies 0FGL J1830.3+0617 as a blazar near the Galactic plane through multiwavelength observations, confirming its variability, radio properties, and optical spectrum, and suggests similar identifications for other low-latitude Fermi sources.

Contribution

First multiwavelength characterization of 0FGL J1830.3+0617 as a blazar, including optical spectroscopy and radio analysis, confirming its classification and proposing identifications for other sources.

Findings

0FGL J1830.3+0617 is a blazar with flat radio spectrum and variability.

Optical spectroscopy shows Mg II emission line at z=0.75.

Additional low-latitude Fermi sources are likely blazars.

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.