IGR J22517+2218=MG3 J225155+2217: a new gamma-ray lighthouse in the distant Universe

TL;DR

This paper reports the discovery and detailed multiwavelength analysis of a distant gamma-ray emitting quasar, IGR J22517+2218, revealing its unique spectral properties and variability, making it a significant new gamma-ray lighthouse in the distant Universe.

Contribution

It presents the identification and characterization of a new distant gamma-ray source with unusual spectral energy distribution and variability, expanding our understanding of high-redshift blazars.

Findings

Detected a new gamma-ray source at z=3.668 with flux ~4 x10^-11 erg cm^-2 s^-1

Observed spectral curvature and variability indicating complex emission processes

Identified as the second most distant blazar detected above 20 keV

Abstract

We report on the identification of a new soft gamma ray source, namely IGR J22517+2218, detected with IBIS/INTEGRAL. The source, which has an observed 20-100 keV flux of ~4 x10^-11 erg cm-2 s-1, is spatially coincident with MG3 J225155+2217, a quasar at z=3.668. The Swift/XRT 0.5-10 keV continuum is flat (Gamma=1.5) with evidence for a spectral curvature below 1-2 keV either due to intrinsic absorption (NH=3 +/- 2 x 10^22 cm-2) or to a change in slope (Delta Gamma= 0.5). X-ray observations indicate flux variability over a 6 days period which is further supported by a flux mismatch between Swift and INTEGRAL spectra. IGR J22517+2218 is radio loud and has a flat radio spectrum; optically it is a broad line emitting quasar with the atypical property of hosting a narrow line absorption system. The Source Spectral Energy Distribution is unusual compared to blazars of similar type: either it has the synchrotron peak in the X/gamma-ray band (i.e. much higher than generally observed) or the Compton peak in the MeV range (i.e. lower than typically measured). IGR J22517+2218=MG3 J225155+2217 is the second most distant blazar detected above 20 keV and a gamma-ray lighthouse shining from the edge of our Universe.