The physical properties of $\gamma$-ray quiet flat-spectrum radio quasars: why are they undetected by $Fermi$-LAT?

TL;DR

This study investigates why certain flat-spectrum radio quasars remain undetected in gamma rays by analyzing their physical properties and spectral energy distributions, suggesting that the location of energy dissipation regions influences gamma-ray detectability.

Contribution

It provides new insights into the physical conditions of gamma-ray quiet FSRQs, highlighting the importance of dissipation region location in gamma-ray emission.

Findings

Dissipation regions farther from the black hole may cause gamma-ray quietness.

Contradicts previous smaller bulk Lorentz factor assumptions.

Spectral energy distribution modeling supports the dissipation region hypothesis.

Abstract

During a decade of the $Fermi$-Large Area Telescope (LAT) operation, thousands of blazars have been detected in the $\gamma$-ray band. However, there are still numbers of blazars that have not been detected in the $\gamma$-ray band. In this work, we focus on investigating why some flat-spectrum radio quasars (FSRQs) are undetected by $Fermi$-LAT. By cross-matching the Candidate Gamma-ray Blazars Survey catalog with the Fourth Catalog of Active Galactic Nuclei Detected by the $Fermi$-LAT, we select 11 $\gamma$-ray undetected ($\gamma$-ray quiet) FSRQs as our sample whose quasi-simultaneous multi-wavelength data are collected. In the framework of the conventional one-zone leptonic model, we investigate their underlying physical properties and study the possibility that they are undetected with $\gamma$-ray by modeling their quasi-simultaneous spectral energy distributions. In contrast to a smaller bulk Lorentz factor suggested by previous works, our results suggest that the dissipation region located relatively far away from the central super-massive black hole is more likely to be the cause of some $\gamma$-ray quiet FSRQs being undetected by $Fermi$-LAT.