THE SPECTRAL ENERGY DISTRIBUTION OF<i>FERMI</i>BRIGHT BLAZARS

TLDR

High‑quality, quasi‑simultaneous spectral energy distributions for 48 Fermi LAT bright AGN were assembled by combining accurately estimated Fermi γ‑ray spectra with contemporaneous Swift, radio, infrared, optical, and hard X‑ray/gamma‑ray data. The SEDs reveal synchrotron peak frequencies ranging from 10^12.5 to 10^14.5 Hz in flat‑spectrum radio quasars and 10^13 to 10^17 Hz in BL Lac objects, with the γ‑ray spectral slope tightly correlated with the synchrotron peak and X‑ray index, while simple one‑zone SSC models fail to explain most sources. Full details are presented in the complete publication.

Abstract

(Abridged) We have conducted a detailed investigation of the broad-band spectral properties of the \gamma-ray selected blazars of the Fermi LAT Bright AGN Sample (LBAS). By combining our accurately estimated Fermi gamma-ray spectra with Swift, radio, infra-red, optical and other hard X-ray/gamma-ray data, collected within three months of the LBAS data taking period, we were able to assemble high-quality and quasi-simultaneous Spectral Energy Distributions (SED) for 48 LBAS blazars.The SED of these gamma-ray sources is similar to that of blazars discovered at other wavelengths, clearly showing, in the usual Log $\nu $ - Log $\nu$ F$_\nu$ representation, the typical broad-band spectral signatures normally attributed to a combination of low-energy synchrotron radiation followed by inverse Compton emission of one or more components. We have used these SEDs to characterize the peak intensity of both the low and the high-energy components. The results have been used to derive empirical relationships that estimate the position of the two peaks from the broad-band colors (i.e. the radio to optical and optical to X-ray spectral slopes) and from the gamma-ray spectral index. Our data show that the synchrotron peak frequency $\nu_p^S$ is positioned between 10$^{12.5}$ and 10$^{14.5}$ Hz in broad-lined FSRQs and between $10^{13}$ and $10^{17}$ Hz in featureless BL Lacertae objects.We find that the gamma-ray spectral slope is strongly correlated with the synchrotron peak energy and with the X-ray spectral index, as expected at first order in synchrotron - inverse Compton scenarios. However, simple homogeneous, one-zone, Synchrotron Self Compton (SSC) models cannot explain most of our SEDs, especially in the case of FSRQs and low energy peaked (LBL) BL Lacs. (...)