Fast $\gamma$-ray variability in blazars beyond redsift 3

TL;DR

This study presents the first systematic analysis of gamma-ray variability in all known high-redshift (z>3) blazars, revealing significant long-term and intraday variability, including the discovery of the most distant gamma-ray flaring blazar.

Contribution

It provides the first comprehensive temporal analysis of gamma-ray variability in high-redshift blazars, including new detections of intraday variations and constraints on their emission regions.

Findings

Five out of seven high-redshift blazars show significant long-term gamma-ray variability.

Intraday gamma-ray variations detected in two sources, with one showing a doubling timescale as short as 1 hour.

NVSS J053954-283956 is identified as the most distant gamma-ray flaring blazar.

Abstract

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