69 research outputs found
The High Redshift Blazar S5 0836+71: A Broadband Study
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
-ray flares, while optical-UV fluxes show little variations. During the
GeV outburst, the highest -ray flux measured is (5.22 1.10)
10 ph cm s in the range of 0.1-300 GeV, which
corresponds to an isotropic -ray luminosity of (1.62 0.44)
10 erg s, thereby making this as one of the most
luminous -ray flare ever observed from any blazar. A fast -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
-ray flare. The high X-ray activity with less variable -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.Comment: 41 pages, 9 figures, 6 tables, to appear in The Astrophysical
Journal. arXiv admin note: text overlap with arXiv:1501.0736
Violent Hard X-ray Variability of Mrk 421 Observed by NuSTAR in 2013 April
The well studied blazar Markarian 421 (Mrk 421, =0.031) was the subject of
an intensive multi-wavelength campaign when it flared in 2013 April. The
recorded X-ray and very high energy (VHE, E100 GeV) -ray fluxes are
the highest ever measured from this object. At the peak of the activity, it was
monitored by the hard X-ray focusing telescope {\it Nuclear Spectroscopic
Telescope Array} ({\it NuSTAR}) and {\it Swift} X-Ray Telescope (XRT). In this
work, we present a detailed variability analysis of {\it NuSTAR} and {\it
Swift}-XRT observations of Mrk 421 during this flaring episode. We obtained the
shortest flux doubling time of 14.015.03 minutes, which is the shortest
hard X-ray (379 keV) variability ever recorded from Mrk 421 and is on the
order of the light crossing time of the black hole's event horizon. A pattern
of extremely fast variability events superposed on slowly varying flares is
found in most of the {\it NuSTAR} observations. We suggest that these peculiar
variability patterns may be explained by magnetic energy dissipation and
reconnection in a fast moving compact emission region within the jet. Based on
the fast variability, we derive a lower limit on the magnetic field strength of
~G, where is the
Doppler factor in units of 10, and is the characteristic X-ray
synchrotron frequency in units of ~Hz.Comment: 23 pages, 5 figures, 2 tables, to appear in the Astrophysical Journa
A hard gamma-ray flare from 3C 279 in 2013 December
The blazar 3C 279 exhibited twin γ-ray flares of similar intensity in 2013 December and 2014 April. In this work, we present a detailed multi-wavelength analysis of the 2013 December flaring event. Multi-frequency observations reveal the uncorrelated variability patterns with X-ray and optical–UV fluxes peaking after the γ-ray maximum. The broadband spectral energy distribution (SED) at the peak of the γ-ray activity shows a rising γ-ray spectrum but a declining optical–UV flux. This observation along with the detection of uncorrelated variability behavior rules out the one-zone leptonic emission scenario. We, therefore, adopt two independent methodologies to explain the SED: a time-dependent lepto-hadronic modeling and a two-zone leptonic radiative modeling approach. In the lepto-hadronic modeling, a distribution of electrons and protons subjected to a randomly orientated magnetic field produces synchrotron radiation. Electron synchrotron is used to explain the IR to UV emission while proton synchrotron emission is used to explain the high-energy γ-ray emission. A combination of both electron synchrotron self-Compton emission and proton synchrotron emission is used to explain the X-ray spectral break seen during the later stage of the flare. In the two-zone modeling, we assume a large emission region emitting primarily in IR to X-rays and γ-rays to come primarily from a fast-moving compact emission region. We conclude by noting that within a span of four months, 3C 279 has shown the dominance of a variety of radiative processes over each other and this reflects the complexity involved in understanding the physical properties of blazar jets in general
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