Seyfert 2 galaxies in the GeV band: jets and starburst
  The Fermi/LAT collaboration recently reported the detection of starburt
galaxies in the high energy gamma-ray domain, as well as radio-loud narrow-line
Seyfert 1 objects, which were previously unusual extragalactic suspects for
high energy emission. Motivated by the presence of sources close to the
location of composite starburst/Seyfert 2 galaxies in the first year Fermi/LAT
catalogue, we studied high energy gamma-ray emission from such objects, aiming
at disentangling the emission of starburst and Seyfert activity. We analysed
1.6 years of Fermi/LAT data from NGC 1068 and NGC 4945, which count among the
brightest Seyfert 2 galaxies. We found an excess of high energy gamma-rays of
8.3 sigmas and 9.2 sigmas for 1FGL J0242.7+0007 and 1FGL J1305.4-4928, which
are found to be consistent with the position of the Seyfert 2 galaxies NGC 1068
and NGC 4945, respectively. While the high energy flux of NGC 4945 is
consistent with starburst activity, that of NGC 1068 is an order of magnitude
above expectations, suggesting dominant emission from the active nucleus. We
show that a leptonic scenario can account for the multi-wavelength spectral
energy distribution of NGC 1068. High energy gamma-ray emission is thus
revealed for the first time in a Seyfert 2 galaxy. If this result is confirmed
in other objects, new perspectives would be opened up into the GeV band, with
the discovery of a new class of high energy gamma-ray emitters.
