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We use the complete MOJAVE 1.5 Jy sample of active galactic nuclei (AGN) to examine the gamma-ray detection statistics of the brightest radio-loud blazars in the northern sky. We find that 23% of these AGN were not detected above 0.1 GeV by the Fermi LAT during the 4-year 3FGL catalog period partly because of an instrumental selection effect, and partly due to their lower Doppler boosting factors. Blazars with synchrotron peaks in their spectral energy distributions located below $10^{13.4}$ Hz also tend to have high-energy peaks that lie below the 0.1 GeV threshold of the LAT, and are thus less likely to be detected by Fermi. The non-detected AGN in the 1.5 Jy sample also have significantly lower 15 GHz radio modulation indices and apparent jet speeds, indicating that they have lower than average Doppler factors. Since the effective amount of relativistic Doppler boosting is enhanced in gamma-rays (particularly in the case of external inverse-Compton scattering), this makes them less likely to appear in the 3FGL catalog. Based on their observed properties, we have identified several bright radio-selected blazars that are strong candidates for future detection by Fermi.
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Multiwavelength observations are essential to constrain physical parameters of the blazars observed by Fermi/LAT. Among the 187 AGN significantly detected in public INTEGRAL data above 20 keV by the imager IBIS/ISGRI, 20 blazars were detected. 15 of these sources allowed significant spectral extraction. They show hard X-ray spectra with an average photon index of 2.1+-0.1 and a hard X-ray luminosity of L(20-100 keV) = 1.3e46 erg/s. 15 of the INTEGRAL blazars are also visible in the first 16 months of the Fermi/LAT data, thus allowing to constrain the inverse Compton branch in these cases. Among others, we analyse the LAT data of four blazars which were not included in the Fermi LAT Bright AGN Sample based on the first 3 months of the mission: QSO B0836+710, H 1426+428, RX J1924.8-2914, and PKS 2149-306. Especially for blazars during bright outbursts, as already observed simultaneously by INTEGRAL and Fermi (e.g. 3C 454.3 and Mrk 421), INTEGRAL provides unique spectral coverage up to several hundred keV. We present the spectral analysis of INTEGRAL and Fermi data and demonstrate the potential of INTEGRAL observations of Fermi detected blazars in outburst by analysing the combined data set of the persistent radio galaxy Cen A.
Blazars are an extreme subclass of active galactic nuclei. Their rapid variability, luminous brightness, superluminal motion, and high and variable polarization are probably due to a beaming effect. However, this beaming factor (or Doppler factor) is very difficult to measure. Currently, a good way to estimate it is to use the time scale of their radio flares. In this $Letter$, we use multiwavelength data and Doppler factors reported in the literatures for a sample of 86 flaring blazars detected by Fermi to compute their intrinsic multiwavelength data and intrinsic spectral energy distributions, and investigate the correlations among observed and intrinsic data. Quite interestingly, intrinsic data show a positive correlation between luminosity and peak frequency, in contrast with the behavior of observed data, and a tighter correlation between $gamma$-ray luminosity and the lower energy ones. For flaring blazars detected by Fermi, we conclude that (1) Observed emissions are strongly beamed; (2) The anti-correlation between luminosity and peak frequency from the observed data is an apparent result, the correlation between intrinsic data being positive; and (3) Intrinsic $gamma$-ray luminosity is strongly correlated with other intrinsic luminosities.
The regular monitoring of flat-spectrum radio quasars (FSRQs) in $gamma$-rays by Fermi-LAT since past 12 years indicated six sources who exhibited extreme $gamma$-ray outbursts crossing daily flux of $10^{-5}$ photons/cm$^{2}$/s. We obtained nearly-simultaneous multi-wavelength data of these sources in radio to $gamma$-ray waveband from OVRO, Steward Observatory, SMARTS, Swift-UVOT, Swift-XRT, and Fermi-LAT. The time-averaged broadband Spectral Energy Distributions (SEDs) of these sources in quiescent states were studied to get an idea about the underlying baseline radiation processes. We modeled the SEDs using one-zone leptonic synchrotron and inverse-Compton emission scenario from broken power-law electron energy distribution inside a spherical plasma blob, relativistically moving down a conical jet. The model takes into account inverse-Compton scattering of externally and locally originated seed photons in the jet. The big blue bumps visible in quiescent state SEDs helped to estimate the accretion disk luminosities and central black hole masses. We found a correlation between the magnetic field inside the emission region and the ratio of emission region distance to disk luminosity, which implies that the magnetic field decreases with an increase in emission region distance and decrease in disk luminosity, suggesting a disk-jet connection. The high-energy index of the electron distribution was also found to be correlated with observed $gamma$-ray luminosity as $gamma$-rays are produced by high-energy particles. In most cases, kinetic power carried by electrons can account for jet radiation power as jets become radiatively inefficient during quiescent states.
By comparing the properties of non-recycled radio-loud $gamma-$ray pulsars and radio-quiet $gamma-$ray pulsars, we have searched for the differences between these two populations. We found that the $gamma-$ray spectral curvature of radio-quiet pulsars can be larger than that of radio-loud pulsars. Based on the full sample of non-recycled $gamma-$ray pulsars, their distributions of the magnetic field strength at the light cylinder are also found to be different. We notice that this might be resulted from the observational bias. In re-examining the previously reported difference of $gamma-$ray-to-X-ray flux ratios, we found the significance can be hampered by their statistical uncertainties. In the context of outer gap model, we discuss the expected properties of these two populations and compare with the possible differences identified in our analysis.
Blazars are a subclass of active galactic nuclei (AGNs) with extreme observation properties, which is caused by the beaming effect, expressed by a Doppler factor, in a relativistic jet. Doppler factor is an important parameter in the blazars paradigm to indicate all of the observation properties, and many methods were proposed to estimate its value. In this paper, we present a method following Mattox et al. to calculate the lower limit on gamma-ray Doppler factor for 809 selected Fermi/LAT-detected gamma-ray blazars by adopting the available gamma-ray and X-ray data. Our sample included 342 flat-spectrum radio quasars (FSRQs) and 467 BL Lac objects (BL Lacs), out of which 507 sources are compiled with available radio core-dominance parameter (R) from our previous study. Our calculation shows that the average values of the lower limit on gamma-ray Doppler factor for FSRQs and BL Lacs are 6.87 and 4.31, respectively. We compare and discuss our results with those from the literature. We found that the derived lower limit on gamma-ray Doppler factor for some sources are higher than that from the radio estimation, which could be possibly explained by the jet bending within those blazars. Our results also suggest that the gamma-ray and radio regions perhaps share the same relativistic effects. The gamma-ray Doppler factor has been found to be correlated with both the gamma-ray luminosity and core-dominance parameter, implying that the jet is possibly continuous in the gamma-ray bands, and R is perhaps an indicator for a beaming effect.
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