Fermi Gamma-ray Space Telescope

Flaring gamma-ray emission from high redshift blazars

Monica Orienti
F. D'Ammando, M. Giroletti, J. Finke, M. Ajello on behalf of the Fermi LAT Collaboration

Abstract:

High redshift blazars are among the most powerful objects in the Universe. Although they represent a significant fraction of the extragalactic hard X-ray sky, they are not commonly detected in gamma-rays. High redshift (z>2) objects represent less than 10 per cent of the AGN population observed by Fermi so far, and gamma-ray flaring activity from these sources is even more uncommon. The characterization of the radio-to-gamma-ray properties of high redshift blazars represent a powerful tool for the study of the energetics of such extreme objects and the Extragalactic Background Light. In this contribution I will present results of a multi-band campaign on TXS 0536+145, which is the highest redshift flaring gamma-ray blazar detected so far. At the peak of the flare the source reached an apparent isotropic gamma-ray luminosity of about 7x10^49 erg/s, which is comparable with the luminosity observed from the most powerful blazars. The physical properties derived from the multi-wavelength observations are then compared with those shown by the high redshift population. In addition preliminary results from the other high redshift flaring blazar PKS 2149-306 will be discussed.