Fermi/LAT Observations of Swift/BAT Seyferts: on the Contribution of Radio-quiet AGN to the Extragalactic Gamma-ray Background

TL;DR

This study analyzes Fermi/LAT data on Swift/BAT Seyfert galaxies, finding only radio-loud ones are detected and setting upper limits on gamma-ray fluxes, while also identifying new Fermi sources near Seyferts.

Contribution

It introduces a new radio-loudness parameter for Seyferts and provides constraints on their gamma-ray emission, highlighting the rarity of gamma-ray detected Seyferts and discovering new Fermi sources.

Findings

Only radio-loud Seyferts are detected in gamma rays.

Upper limits on gamma-ray flux for undetected Seyferts are established.

120 new Fermi/LAT sources are identified near Seyfert galaxies.

Abstract

We present the analysis of 2.1 years of Fermi/LAT data on 491 Seyfert galaxies detected by the Swift/BAT survey. Only the two nearest objects, NGC 1068 and NGC 4945, which were identified in the Fermi First-year Catalog, are detected. Using the Swift/BAT and radio 20 cm fluxes, we define a new radio-loudness parameter $R_{X, BAT}$ where radio loud objects have $\log R_{X, BAT} > - 4.7$. Based on this parameter, only radio loud sources are detected by Fermi/LAT. An upper limit to the flux of the undetected sources is derived to be $\sim 2 \times 10^{-11}$ photons cm$^{-2}$ s$^{-1}$, approximately seven times lower than the observed flux of NGC 1068. Assuming a median redshift of 0.031, this implies an upper limit to the $\gamma$-ray (1--100 GeV) luminosity of $\lesssim 3 \times 10^{41}$ erg s$^{-1}$. In addition, we identified 120 new Fermi/LAT sources near the Swift/BAT Seyferts with significant Fermi/LAT detections. A majority of these objects do not have \bat counterparts, but their possible optical counterparts include blazars, FSRQs, and quasars.