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Perley D.A.,California Institute of Technology | Cenko S.B.,NASA | Cenko S.B.,University of California at Berkeley | Cenko S.B.,University of Maryland University College | And 34 more authors.
Astrophysical Journal | Year: 2014

We present multiwavelength observations of the afterglow of GRB 130427A, the brightest (in total fluence) gamma-ray burst (GRB) of the past 29 yr. Optical spectroscopy from Gemini-North reveals the redshift of the GRB to be z = 0.340, indicating that its unprecedented brightness is primarily the result of its relatively close proximity to Earth; the intrinsic luminosities of both the GRB and its afterglow are not extreme in comparison to other bright GRBs. We present a large suite of multiwavelength observations spanning from 300 s to 130 days after the burst and demonstrate that the afterglow shows relatively simple, smooth evolution at all frequencies, with no significant late-time flaring or rebrightening activity. The entire data set from 1 GHz to 10 GeV can be modeled as synchrotron emission from a combination of reverse and forward shocks in good agreement with the standard afterglow model, providing strong support to the applicability of the underlying theory and clarifying the nature of the GeV emission observed to last for minutes to hours following other very bright GRBs. A tenuous, wind-stratified circumburst density profile is required by the observations, suggesting a massive-star progenitor with a low mass-loss rate, perhaps due to low metallicity. GRBs similar in nature to GRB 130427A, inhabiting low-density media and exhibiting strong reverse shocks, are probably not uncommon but may have been difficult to recognize in the past owing to their relatively faint late-time radio emission; more such events should be found in abundance by the new generation of sensitive radio and millimeter instruments. © 2014. The American Astronomical Society. All rights reserved. Source


Kutkin A.M.,RAS Lebedev Physical Institute | Sokolovsky K.V.,RAS Lebedev Physical Institute | Lisakov M.M.,RAS Lebedev Physical Institute | Kovalev Y.Y.,Max Planck Institute for Radio Astronomy | And 9 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2014

Opacity-driven shifts of the apparent very long baseline interferometry (VLBI) core position with frequency (the 'core shift' effect) probe physical conditions in the innermost parts of jets in active galactic nuclei. We present the first detailed investigation of this effect in the brightest γ -ray blazar 3C 454.3 using direct measurements from simultaneous 4.6-43 GHz very long baseline array observations, and a time lag analysis of 4.8-37 GHz light curves from the University of Michigan Radio Observatory, Crimean Astrophysical Observatory and Mets̈ahovi observations in 2007-2009. The results support the standard K̈onigl model of jet physics in the VLBI core region. The distance of the core from the jet origin rc(v), the core size w(v) and the light curve time lag δT(v) all depend on the observing frequency v as rc(v) ∝ δ(v) δT(v) ∝ δ v-1/k. The obtained range of k = 0.6-0.8 is consistent with the synchrotron self-absorption being the dominating opacity mechanism in the jet. The similar frequency dependence of rc(v) and W(v) suggests that the external pressure gradient does not dictate the jet geometry in the cm-band core region. Assuming equipartition, the magnetic field strength scales with distance r as B = 0.4(r/1 pc)-0.8G. The total kinetic power of electron/positron jet is about 1044 ergs s-1. © 2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. Source


Morozova D.A.,Saint Petersburg State University | Larionov V.M.,Saint Petersburg State University | Troitsky I.S.,Saint Petersburg State University | Jorstad S.G.,Saint Petersburg State University | And 23 more authors.
Astronomical Journal | Year: 2014

We present the results of optical (R-band) photometric and polarimetric monitoring and Very Long Baseline Array imaging of the blazar S4 0954+658, along with Fermi γ-ray data during a multi-waveband outburst in 2011 March-April. After a faint state with a brightness level R 17.6 mag registered in the first half of 2011 January, the optical brightness of the source started to rise and reached 14.8 mag during the middle of March, showing flare-like behavior. The most spectacular case of intranight variability was observed during the night of 2011 March 9, when the blazar brightened by 0.7 mag within 7 hr. During the rise of the flux, the position angle of the optical polarization rotated smoothly over more than 300°. At the same time, within 1σ uncertainty, a new superluminal knot appeared with an apparent speed of 19.0 ± 0.3c. We have very strong evidence that this knot is associated with the multi-waveband outburst in 2011 March-April. We also analyze the multi-frequency behavior of S4 0954+658 during a number of minor outbursts from 2008 August to 2012 April. We find some evidence of connections between at least two additional superluminal ejecta and near-simultaneous optical flares. © 2014. The American Astronomical Society. All rights reserved.. Source


Vol'vach A.E.,Radio Astronomy Laboratory of the Crimean Astrophysical Observatory | Kutkin A.M.,RAS Lebedev Physical Institute | Larionov M.G.,RAS Lebedev Physical Institute | Vol'vach L.N.,Radio Astronomy Laboratory of the Crimean Astrophysical Observatory | And 8 more authors.
Astronomy Reports | Year: 2013

We present an analysis of data from multi-frequency monitoring of the blazar 3C 454. 3 in 2010-2012, when the source experienced an unusually prolonged flare with a duration of about two years. This corresponds to the orbital period of the companion in a scenario in which two supermassive black holes are present in the nucleus of 3C 454.3. The flare's shape, duration, and amplitude can be explained as a result of precession, if the plane of the accretion disk and the orbital plane of the binary are coincident. We detected small-scale structure of the flare, on time scales of no more than a month. These features probably correspond to inhomogeneities in the accretion disk and surrounding regions, with sizes of the order of 1015 cm. We estimated the size of the accretion disk based on the dynamical and geometrical parameters of this binary system: its diameter is comparable to the size of the orbit of the supermassive binary black hole, and its thickness does not exceed the gravitational radius of the central black hole. The presence of characteristic small-scale features during the flare makes it possible to estimate the relative time delays of variations in different spectral ranges: from gamma-ray to millimeter wavelengths. © 2013 Pleiades Publishing, Ltd. Source

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