Fermi LAT detection of a GeV gamma-ray flare from blazar CGRaBS J0809+5341 (87GB 080551.6+535010)

The Large Area Telescope (LAT), one of two instruments on the Fermi Gamma-ray Space Telescope, has observed increasing gamma-ray emission from a source positionally consistent with the flat spectrum radio quasar CGRaBS J0809+5341 (also known as 87GB 080551.6+535010, BZQ J0809+5341 and 3FGL J0809.5+5342) with radio coordinates (J2000) R.A. 122.4238862 deg, Dec. 53.6903033 deg (Petrov et al. 2011, AJ, 142, 89). This blazar has a redshift z = 2.133 (Healey et al. 2008, ApJS, 175, 97). Preliminary analysis indicates that on 2017 October 26, CGRaBS J0809+5341 was in a high state with a daily averaged gamma-ray flux (E > 100 MeV) of (0.23+/-0.15) X 10^-6 photons cm^-2 s^-1 (statistical uncertainty only), about 20 times greater than its four-year average flux reported in the third Fermi-LAT source catalog (3FGL, Acero et al. 2015, ApJS, 218, 23). Because Fermi operates in an all-sky scanning mode, regular gamma-ray monitoring of this source will continue.