A gamma-ray flare from TXS 1508+572: characterizing the jet of a $z=4.31$ blazar in the early Universe

TL;DR

This paper reports the first detection of a gamma-ray flare from the high-redshift blazar TXS 1508+572 at z=4.31, using multiwavelength observations to analyze its jet properties and emission mechanisms in the early Universe.

Contribution

It presents the first gamma-ray flare detection from a z>4 blazar and provides a detailed multiwavelength analysis of its jet emission during this event.

Findings

Detected a gamma-ray flare from TXS 1508+572 at z=4.31.

The flare reached luminosity comparable to the most luminous Fermi-LAT flares.

The spectral energy distribution is explained by a one-zone leptonic model with external Compton emission.

Abstract

Blazars can be detected from very large distances due to their high luminosity. However, the detection of $\gamma$-ray emission of blazars beyond $z=3$ has only been confirmed for a small number of sources. Such observations probe the growth of supermassive black holes close to the peak of star formation in the history of galaxy evolution. As a result from a continuous monitoring of a sample of 80 $z>3$ blazars with Fermi-LAT, we present the first detection of a $\gamma$-ray flare from the $z=4.31$ blazar TXS 1508+572. This source showed high $\gamma$-ray activity from February to August 2022, reaching a peak luminosity comparable to the most luminous flares ever detected with Fermi -LAT. We conducted a multiwavelength observing campaign involving XMM-Newton, Swift, the Effelsberg 100-m radio telescope and the Very Long Baseline Array. In addition, we make use of the monitoring programs by the Zwicky Transient Facility and NEOWISE at optical and infrared wavelengths, respectively. We find that the source is particularly variable in the infrared band on daily time scales. The spectral energy distribution collected during our campaign is well described by a one-zone leptonic model, with the $\gamma$-ray flare originating from an increase of external Compton emission as a result of a fresh injection of accelerated electrons.