Astronomy and Astrophysics – Astronomy
Scientific paper
Jan 2012
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2012aas...21930506h&link_type=abstract
American Astronomical Society, AAS Meeting #219, #305.06
Astronomy and Astrophysics
Astronomy
Scientific paper
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 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 positionally coincident with any target Seyferts, with possible exceptions of ESO 323-G077 and NGC 6814. The typical value of the 95 % confidence level gamma-ray upper limit for the integrated photon flux above 100 MeV from the analyzed Seyferts is on the order of 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.
Bechtol Keith
Fermi-LAT
Hayashida Masaaki
Madejski Greg
Stawarz Lucasz
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