Search for Gamma-ray Emission from X-ray Selected Seyfert Galaxies with Fermi-LAT

TL;DR

This study systematically searched for gamma-ray emission from 120 radio-quiet Seyfert galaxies using Fermi-LAT data but found no significant gamma-ray signals, setting upper limits that constrain models of high-energy emission in these galaxies.

Contribution

First comprehensive gamma-ray search for X-ray selected radio-quiet Seyfert galaxies with Fermi-LAT, establishing upper limits and constraining emission models.

Findings

No significant gamma-ray excess detected in the sample.

Upper limits on gamma-ray flux constrain the gamma-ray to X-ray luminosity ratio.

Results impose new constraints on high-energy emission models for Seyfert galaxies.

Abstract

We report on a systematic investigation of the gamma-ray properties of 120 hard X-ray-selected Seyfert galaxies classified as `radio-quiet' objects, utilizing the three-year accumulation of Fermi-LAT data. Our sample of Seyfert galaxies is selected using the Swift-BAT 58-month catalog, restricting the analysis to the bright sources with average hard X-ray fluxes F(14-195 keV) > 2.5x10-11 erg cm-2 s-1 at high Galactic latitudes (|b|>10 deg). In order to remove `radio-loud' objects from the sample, we use the `hard X-ray radio loudness parameter', Rrx, defined as the ratio of the total 1.4 GHz radio to 14-195 keV hard X-ray energy fluxes. Among 120 X-ray bright Seyfert galaxies with Rrx <10-4, we did not find a statistically significant gamma-ray excess (TS>25) positionally coincident with any target Seyferts, with possible exceptions of ESO 323-G077 and NGC 6814. The mean value of the 95 % confidence level gamma-ray upper limit for the integrated photon flux above 100 MeV from the analyzed Seyferts is ~ 4 x 10-9 ph cm-2 s-1 and the upper limits derived for several objects reach ~ 1 x 10-9 ph cm-2 s-1. Our results indicate that no prominent gamma-ray emission component related to active galactic nucleus activity is present in the spectra of Seyferts around GeV energies. The Fermi-LAT upper limits derived for our sample probe the ratio of gamma-ray to X-ray luminosities Lg/LX < 0.1, and even <0.01 in some cases. The obtained results impose novel constraints on the models for high energy radiation of `radio-quiet' Seyfert galaxies.