The Fermi-LAT Collaboration
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.
View original:
http://arxiv.org/abs/1109.4678
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