Fermi/Large Area Telescope Discovery of Gamma-Ray Emission from a Relativistic Jet in the Narrow-Line Quasar PMN J0948+ 0022
Abdo, A. A. AA ; Ackermann, M. ; Ajello, M. ; Cavazzuti, E. ;
Jul - 2009
ISSN : 0004-637X ;
journal : The Astrophysical Journal

Issue : 2
type: Article Journal

Abstract
We report the discovery by the Large Area Telescope (LAT) onboard the Fermi Gamma-Ray Space Telescope of high-energy ³-ray emission from the peculiar quasar PMN J0948+0022 (z = 0.5846). The optical spectrum of this object exhibits rather narrow H² (FWHM(H²) <1500 km s1), weak forbidden lines, and is therefore classified as a narrow-line type I quasar. This class of objects is thought to have relatively small black hole mass and to accrete at a high Eddington ratio. The radio loudness and variability of the compact radio core indicate the presence of a relativistic jet. Quasi-simultaneous radio/optical/X-ray and ³-ray observations are presented. Both radio and ³-ray emissions (observed over five months) are strongly variable. The simultaneous optical and X-ray data from Swift show a blue continuum attributed to the accretion disk and a hard X-ray spectrum attributed to the jet. The resulting broadband spectral energy distribution (SED) and, in particular, the ³-ray spectrum measured by Fermi are similar to those of more powerful Flat-Spectrum Radio Quasars (FSRQs). A comparison of the radio and ³-ray characteristics of PMN J0948+0022 with the other blazars detected by LAT shows that this source has a relatively low radio and ³-ray power with respect to other FSRQs. The physical parameters obtained from modeling the SED also fall at the low power end of the FSRQ parameter region discussed in Celotti \& Ghisellini. We suggest that the similarity of the SED of PMN J0948+0022 to that of more massive and more powerful quasars can be understood in a scenario in which the SED properties depend on the Eddington ratio rather than on the absolute power.

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