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Register a new userThe Spectral Energy Distributions of Fermi Blazars
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(Abridged) In this paper, multi-wavelength data are compiled for a sample of 1425 Fermi blazars to calculate their spectral energy distributions (SEDs). A parabolic function, $log( u F_{ u}) = P_1(log u - P_2)^2 + P_3,$ is used for SED fitting. Synchrotron peak frequency ($log u_p$), spectral curvature ($P_1$), peak flux ($ u_{rm p}F_{rm u_p}$), and integrated flux ($ u F_{ u}$) are successfully obtained for 1392 blazars (461 flat spectrum radio quasars-FSRQs, 620 BL Lacs-BLs and 311 blazars of uncertain type-BCUs, 999 sources have known redshifts). Monochromatic luminosity at radio 1.4 GHz, optical R band, X-ray at 1 keV and $gamma$-ray at 1 GeV, peak luminosity, integrated luminosity and effective spectral indexes of radio to optical ($alpha_{rm RO}$), and optical to X-ray ($alpha_{rm OX}$) are calculated. The Bayesian classification is employed to log$ u_{rm p}$ in the rest frame for 999 blazars with available redshift and the results show that 3 components are enough to fit the $log u_{rm p}$ distribution, there is no ultra high peaked subclass. Based on the 3 components, the subclasses of blazars using the acronyms of Abdo et al. (2010a) are classified, and some mutual correlations are also studied. Conclusions are finally drawn as follows: (1) SEDs are successfully obtained for 1392 blazars. The fitted peak frequencies are compared with common sources from samples available (Sambruna et al. 1996, Nieppola et al. 2006, 2008, Abdo et al. 2010a). (2) Blazars are classified as low synchrotron peak sources (LSPs) if $log u_{rm p}$(Hz) $leq 14.0$, intermediate synchrotron peak sources (ISPs) if $14.0 < log u_{rm p}$(Hz) $leq 15.3$, and high synchrotron peak sources (HSPs) if $log u_{rm p}$(Hz) $> 15.3$. (3) $gamma$-ray emissions are strongly correlated with radio emissions. (...)
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(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 $ u $ - Log $ u$ F$_ u$ 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 $ u_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. (...)
We present multiwavelength spectral analyses of two Fermi-LAT blazars, OJ 287 and 3C 279, that are part of the Boston University multiwaveband polarization program. The data have been compiled from observations with Fermi, RXTE, the VLBA, and various ground-based optical and radio telescopes. We simulate the dynamic spectral energy distributions (SEDs) within the framework of a multi-slice, time-dependent leptonic jet model for blazars, with radiation feedback, in the internal shock scenario. We use the physical jet parameters obtained from the VLBA monitoring to guide our modeling efforts. We discuss the role of intrinsic parameters and the interplay between synchrotron and inverse Compton radiation processes responsible for producing the resultant SEDs.
We present a determination of the distributions of gamma-ray photon flux -- the so called LogN-LogS relation -- and photon spectral index for blazars, based on the third extragalactic source catalog of the Fermi Gamma-ray Space Telescopes Large Area Telescope, and considering the photon energy range from 100 MeV to 100 GeV. The dataset consists of the 774 blazars in the so-called Clean sample detected with a greater than approximately seven sigma detection threshold and located above $pm$20 deg Galactic latitude. We use non-parametric methods verified in previous works to reconstruct the intrinsic distributions from the observed ones which account for the data truncations introduced by observational bias and includes the effects of the possible correlation between the flux and photon index. The intrinsic flux distribution can be represented by a broken power law with a high flux power-law index of -2.43$pm$0.08 and a low flux power-law index of -1.87$pm$0.10. The intrinsic photon index distribution can be represented by a Gaussian with mean of 2.62$pm$0.05 and width of 0.17$pm$0.02. We also report the intrinsic distributions for the sub-populations of BL Lac and FSRQ type blazars separately and these differ substantially. We then estimate the contribution of FSRQs and BL Lacs to the diffuse extragalactic gamma-ray background radiation. Under the simplistic assumption that the flux distributions probed in this analysis continue to arbitrary low flux, we calculate that the best fit contribution of FSRQs is 35% and BL Lacs 17% of the total gamma-ray output of the Universe in this energy range.
We collect data from the radio to the gamma-ray range for three complete samples of blazars: the Slew Survey and the 1Jy samples of BL Lacs and the 2Jy sample of Flat Spectrum Radio-Loud Quasars (FSRQs). The fraction of objects detected in gamma-rays (E > 100 MeV) is 17%, 26% and 40% in the three samples respectively. Except for the Slew Survey sample, gamma-ray detected sources do not differ either from other sources in each sample, nor from all the gamma-ray detected sources, in terms of the distributions of redshift, radio and X-ray luminosities and of the broad band spectral indices (radio to optical and radio to X-ray). We compute average Spectral Energy Distributions (SEDs) from radio to gamma rays for groups of blazars binned according to radio luminosity, irrespective of the original classification as BL Lac or FSRQ. The resulting SEDs show a remarkable continuity in that: i) the first peak occurs in different frequency ranges for different luminosity classes, with most luminous sources peaking at lower frequencies; ii) the peak frequency of the gamma-ray component correlates with the peak frequency of the lower energy one; iii) the luminosity ratio between the high and low frequency components increases with bolometric luminosity. The continuity of properties among different classes of blazars and the systematic trends of the SEDs as a function of luminosity favor a unified view of the blazar phenomenon: a single parameter, related to luminosity, seems to govern the physical properties and radiation mechanisms in the relativistic jets present in BL Lac objects as well as in FSRQ. The general implications of this unified scheme are discussed.
The GeV break in spectra of the blazar 3C 454.3 is a special observation feature that has been discovered by the {it Fermi}-LAT. The origin of the GeV break in the spectra is still under debate. In order to explore the possible source of GeV spectral break in 3C 454.3, a one-zone homogeneous leptonic jet model, as well as the {it McFit} technique are utilized for fitting the quasi-simultaneous multi-waveband spectral energy distribution (SED) of 3C 454.3. The outside border of the broad-line region (BLR) and inner dust torus are chosen to contribute radiation in the model as external, seed photons to the external-Compton process, considering the observed $gamma$-ray radiation. The combination of two components, namely the Compton-scattered BLR and dust torus radiation, assuming a broken power-law distribution of emitted particles, provides a proper fitting to the multi-waveband SED of 3C 454.3 detected 2008 Aug 3 - Sept 2 and explains the GeV spectral break. We propose that the spectral break of 3C 454.3 may originate from an inherent break in the energy distribution of the emitted particles and the Klein-Nishina effect. A comparison is performed between the energy density of the external photon field for the whole BLR $U_{rm BLR}$ achieved via model fitting and that constrained from the BLR data. The distance from the position of the $gamma$-ray radiation area of 3C 454.3 to the central black hole could be constrained at $sim 0.78$pc ($sim 4.00 R_{rm BLR}$, the size of the BLR).
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