Fast γ-Ray Variability in Blazars beyond Redshift 3

Abstract

High-redshift blazars are one of the most powerful sources in the universe and γ -ray variability carries crucial information about their relativistic jets. In this work we present results of the first systematical temporal analysis of Fermi -LAT data of all known seven γ -ray blazars beyond redshift 3. Significant long-term γ -ray variability is found from five sources in monthly γ -ray light curves, in which three of them are reported for the first time. Furthermore, intraday γ -ray variations are detected from NVSS J053954−283956 and NVSS J080518+614423. The doubling variability timescale of the former source is limited as short as ≲1 hr (at the source frame). Together with variability amplitude over one order of magnitude, NVSS J053954−283956 is the most distant γ -ray flaring blazar so far. Meanwhile, intraday optical variability of NVSS J163547+362930 is found based on an archival PTF/iPTF light curve. Benefiting from the multi-wavelength activity of these sources, constraints on their Doppler factors, as well as the locations of the γ -ray radiation region and indications for the SDSS high redshift jetted active galactic nuclei deficit are discussed.