Radio variability of a Fermi large area telescope bright source 0FGL J1847.8+3223

Radio variability was detected at 1.42GHz from an area at the center of which a Fermi Large Area Telescope (LAT) bright source 0FGL J1847.8+3223 (B2 1846+32A) was located. The flux was detected using a two-element interferometer setup at the Waseda Nasu Observatory; the flux was at least 1200mJy in 2004 and at least 1600mJy in 2005. The flux of B2 1846+32A was 532mJy in the 1980s, as observed by the Greenbank 300 telescope, and 516mJy in the 1990s, as observed by the Very Large Array. Thus, the flux tripled from the mid-1990s to the mid-2000s in the 1.4GHz band. In the 1980s and 1990s, a few observations of B2 1846+32A were carried out; however, variability in flux was not detected. In 2008, 8.800e-08 photon(100 MeV-1 GeV) cm^-2 s^-1 and 6.400e-09 photon(1 GeV-100 GeV) cm^-2 s^-1 gamma rays were detected from B2 1846+32A by the LAT. Gamma rays had not been detected from this source by EGRET in 1991-2000. The gamma-ray flux strengthened at least twice in about 10 years. The upper limit around this source by EGRET is approximately 4.9e-08 photon(>100 MeV) cm^-2 s^-1. The flux of B2 1846+32A strengthened in the 2000s, as indicated by both radio and gamma-ray measurements. These results suggest that there exists a strong correlation between the radio radiation and the gamma-ray emission. In this Letter, we present the analytical results of a strong fringe in the area including B2 1846+32A.