Awakening of the high-redshift blazar CGRaBS J0809+5341

Abstract

CGRaBS J0809+5341, a high-redshift blazar at z = 2.144, underwent a giant optical outburst on 2014 April 19 when it brightened by ~5 mag and reached an unfiltered apparent magnitude of 15.7 mag. This implies an absolute magnitude of −30.5 mag, making it one of the brightest quasars in the universe. This optical flaring triggered us to carry out observations during the decaying part of the flare covering a wide energy range using the Nuclear Spectroscopic Telescope Array, Swift, and ground-based optical facilities. For the first time, the source is detected in γ-rays by the Large Area Telescope on board the Fermi Gamma-Ray Space Telescope. A high optical polarization of ~10% is also observed. Using the Sloan Digital Sky Survey spectrum, the accretion disk luminosity and black hole mass are estimated as 1.5 × 1045 erg s−1 and 108.4 M⊙, respectively. Using a single zone leptonic emission model, we reproduce the spectral energy distribution of the source during the flaring activity. This analysis suggests that the emission region is probably located outside the broad-line region, and the jet becomes radiatively efficient. We also show that the overall properties of CGRaBS J0809+5341 seem to not be in agreement with the general properties observed in high-redshift blazars up to now.