The High Redshift Blazar S5 0836+71: A Broadband Study

Abstract

A broadband study of the high redshift blazar S5 0836+71 (z = 2.172) is presented. Multi-frequency light curves show multiple episodes of X-ray and γ-ray flares, while optical-UV fluxes show little variations. During the GeV outburst, the highest γ-ray flux measured is (5.22 ± 1.10) × 10−6 ph cm^(−2) s^−1 in the range of 0.1-300 GeV, which corresponds to an isotropic γ-ray luminosity of (1.62 ± 0.44) × 1050 erg s^−1, thereby making this as one of the most luminous γ-ray flare ever observed from any blazar. A fast γ-ray flux rising time of ∼3 hours is also noticed which is probably the first measurement of hour scale variability detected from a high redshift (z > 2) blazar. The various activity states of S5 0836+71 are reproduced under the assumption of single zone leptonic emission model. In all the states, the emission region is located inside the broad line region, and the optical-UV radiation is dominated by the accretion disk emission. The modeling parameters suggests the enhancement in bulk Lorentz factor as a primary cause of the γ-ray flare. The high X-ray activity with less variable γ-ray counterpart can be due to emission region to be located relatively closer to the black hole where the dominating energy density of the disk emission results in higher X-ray flux due to inverse-Compton scattering of disk photons.

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