A Multiwavelength Study of Distant Blazar PKS 0537-286
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A MULTIWAVELENGTH STUDY OF DISTANT BLAZAR PKS 0537-286
N. Sahakyan1,2, D. Israyelyan1, and G. Harutyunyan1
We report the results of broadband observations of distant blazar PKS 0537-286 ( z
3.1 ) using data
spanning more than ten years from the Fermi Large Area Telescope together with Swift UVOT/XRT archival data taken between 2005 and 2017. In the J -ray band, the peak flux above 100 MeV, FJ
(6.23 r 0.56) 10 7 photon cm-2 s-1 observed on MJD 57874 within one week, corresponds to
2.46 10 49 erg s-1 isotropic J -ray luminosity. The Swift XRT data analyses show that the X-ray emission is characterized by a significantly hard photon index, *X-ray d 1.3 , and an X-ray flux of LJ
4 10 12 erg cm-2 s-1, which is almost constant over twelve years. The spectral energy distribution is
modeled within one-zone leptonic models assuming the emission region is within the broad-line region. The observed X-ray and J -ray data are modeled as inverse Compton scattering of (i) only synchrotron photons and (ii) synchrotron and external photons on the electron population that produces the radioto-optical emission. The modeling shows that the nonthermal electrons in the jet of PKS 0537-286 have a hard power-law index (100 MeV) show that the extragalactic J -ray sky is dominated by the emission from Active Galactic Nuclei (AGN) of different types [1]. Interestingly, the J -ray emission was observed not only from the most extreme subclass of AGNs (blazars) but also from radio galaxies [2-5] and Seyfert galaxies [6]. This provides an exceptional chance to investigate the relativistic processes under different conditions. In the unification scheme of AGNs [7], blazars are a subclass of AGNs with relativistic jets oriented close to our line of sight. Blazars are known to emit electromagnetic emission ranging from radio to very high energy J -ray bands (VHE > 100 GeV) which is characterized by high amplitude and short time scale variability. The most
extreme time scale variability is observed in the HE and VHE J -ray bands when the flux amplification time scale can be as short as minute scales (e.g., [8-10]). Depending on the emission line properties, blazars are usually subgrouped into flat spectrum radio quasars (FSRQs) and BL Lac objects, where BL Lacs have no or weak emission lines, while in FSRQs the emission lines are stronger and quasar-like [7]. Blazars being powerful sources were always considered as effective neutrino emitters. This association was strengthened by the recent association of TXS 0506+056 with the neutrino event IceCube-170922A [11-13] which opened new perspectives for studying blazars, using multimessenger data (e.g., [14-18]). The blazar spectral energy distribution (SED) is characterized by two broad peaks of which the lower energy (IR/optical/UV/) one is due to the synchrotron emission of electrons in the jet while the origin of the second peak (at HE J -ray band) is unknown. It is commonly described by inverse Compton scattering of the synchrotron photons or photons external to the jet (e.g., for t
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