High redshift Fermi blazars observed by GROND and Swift

TL;DR

This study presents quasi-simultaneous multiwavelength observations of five high-redshift Fermi blazars, revealing accretion disc properties, jet parameters, and an exceptional IR-optical brightening event, enhancing understanding of their energetic processes.

Contribution

It provides the first comprehensive spectral energy distribution analysis of all z>2 Fermi blazars with X-ray data, linking accretion rates to jet power with new observational insights.

Findings

Detection of accretion discs in 4 blazars and estimation of their black hole masses.

Observation of an extraordinary IR-optical brightening in PKS 1348+007.

Jet physical parameters consistent with those of other gamma-ray loud quasars.

Abstract

We observed 5 gamma-ray loud blazars at redshift greater than 2 with the X-Ray Telescope (XRT) and the UltraViolet and Optical Telescope (UVOT) onboard the Swift satellite, and the Gamma-Ray burst Optical Near-Infrared Detector (GROND) instrument. These observations were quasi simultaneous, usually within a few hours. For 4 of these blazars the near-IR to UV data show the presence of an accretion disc, and we could reliably estimate its accretion rate and black hole mass. One of them, PKS 1348+007, was found in an extraordinarily high IR-optical state, almost two orders of magnitude brighter than at the epoch of the Sloan Digital Sky Survey observations. For all the 5 quasars the physical parameters of the jet emitting zone, derived by applying a one-zone emission model, are similar to that found for the bulk of other gamma-ray loud quasars. With our observations we have X-ray data for the full sample of blazars at z>2 present in the Fermi 2-yrs (2LAC) catalog. This allows to have a rather complete view of the spectral energy distribution of all high-redshift Fermi blazars, and to draw some conclusions about their properties, and especially about the relation between the accretion rate and the jet power.