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In this work, spectral energy distribution has been calculated for a sample of 597 Fermi blazars. Based on the calculation, we proposed a classification for subclasses of blazars as lower synchrotron peak sources (LSPs) if , intermediate synchrotron peak sources (ISPs) if , higher synchrotron peak sources (HSPs) if , ultra higher synchrotron peak sources (UHSPs) if . -ray luminosity is found correlated with lower energetic wavebands (radio, optical and X-rays). When redshift effect is removed, correlations are still strong for FSRQs; As for BL lacertaes, correlation between -ray and radio or between -ray and optical band is strong, but that between -ray and X-ray is only marginal. [ABSTRACT FROM AUTHOR]

3C 273 is a well-studied FSRQ. In order to analyze its spectrum variabilities, we make spectroscopic observations of 3C 273 using the 2.16 m telescope at Xinglong Observatory of the National Astronomical Observatories. Based on these observations and some other spectra from the literature, we study the spectrum variabilities and the physical origin of the optical spectrum. The main results are as follows: (1) The continuum spectrum (S c ) shows obvious variabilities and displays quasi-periodic properties, P = 3.39 ± 1.13 yr, consistent with the result calculated from photometric observations. (2) The spectral energy distribution (SED) was modeled by a combination of blackbody emission that originated from the accretion disk and the dusty torus, synchrotron emission from the jet, the synchrotron self-Compton (SSC) emission, and the external Compton (EC) emission from the broad-line region, accretion disk, and dusty torus. The SED suggests that the optical continuum is dominated by the thermal emission from the accretion disk. (3) A time delay of τ c H β = 209.42 ± 9.38 days lies between the slope of the continuum spectrum (S c ) and H β emission line. (4) The relationships between the spectrum and polarization can be explained by the jet model. [ABSTRACT FROM AUTHOR]

We present a multiwavelength spectral and temporal analysis of the blazar OJ 287 during its recent activity between 2015 December and 2016 May, showing strong variability in the nearinfrared (NIR) to X-ray energies with detection at γ -ray energies as well. Most of the optical flux variations exhibit strong changes in polarization angle and degree. All the interband time lags are consistent with simultaneous emissions. Interestingly, on days with excellent data coverage in the NIR-UV bands, the spectral energy distributions (SEDs) show signatures of bumps in the visible-UV bands, never seen before in this source. The optical bump can be explained as accretion-disc emission associated with the primary black hole of mass ~1.8 × 1010 M☉ while the little bump feature in the optical-UV appears consistent with line emission. Further, the broad-band SEDs extracted during the first flare and during a quiescent period during this span show very different γ -ray spectra compared to previously observed flare or quiescent spectra. The probable thermal bump in the visible seems to have been clearly present since 2013 May, as found by examining all available NIR-optical observations, and favours the binary supermassive black hole model. The simultaneous multiwavelength variability and relatively weak γ -ray emission that shows a shift in the SED peak is consistent with γ -ray emission originating from inverse Compton scattering of photons from the line emission that apparently contributes to the little blue bump. [ABSTRACT FROM AUTHOR]