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The short gamma-ray burst (GRB) 170817A was the first GRB associated with a gravitational-wave event. Due to the exceptionally low luminosity of the prompt γ-ray and the afterglow emission, the origin of both radiation components is highly debated. The most discussed models for the burst and the afterglow include a regular GRB jet seen off-axis and the emission from the cocoon encompassing a >choked> jet. Here, we report low radio frequency observations at 610 and 1390 MHz obtained with the Giant Metrewave Radio Telescope. Our observations span a range of ∼7 to ∼152 days after the burst. The afterglow started to emerge at these low frequencies about 60 days after the burst. The 1390 MHz light curve barely evolved between 60 and 150 days, but its evolution is also marginally consistent with an F ∝ t rise seen in higher frequencies. We model the radio data and archival X-ray, optical, and high-frequency radio data with models of top-hat and Gaussian structured GRB jets. We performed a Markov Chain Monte Carlo analysis of the structured-jet parameter space. Though highly degenerate, useful bounds on the posterior probability distributions can be obtained. Our bounds of the viewing angle are consistent with that inferred from the gravitational-wave signal. We estimate the energy budget in prompt emission to be an order of magnitude lower than that in the afterglow blast wave.© 2018. The American Astronomical Society. All rights reserved. ; We thank Avishay Gal-Yam and Doron Kushnir for using the high-performance computing (HPC) facility WEXAC at the Weizmann Institute of Science. The Weizmann HPC facility is partly supported by the Israel Atomic Energy Commission-The Council for Higher Education-Pazi Foundation and partly by a research grant from The Abramson Family Center for Young Scientists. Development of the BOXFIT code was supported in part by NASA through grant NNX10AF62G issued through the Astrophysics Theory Program and by the NSF through grant AST-1009863. Simulations for BOXFIT version 2 have been carried out in part on the computing facilities of the Computational Center for Particle and Astrophysics (C2PAP) of the research cooperation >Excellence Cluster universe> in Garching, Germany. This work made use of the IAA-CSIC high-performance (HPC) and throughput (HTC) computing infrastructure. R.L. acknowledges support from the grant EMR/2016/007127 from Department of Science and Technology, India. R.L. thanks M. Govindankutty (IIST, Trivandrum) for generously providing computing facilities and ICTS, Bangalore for hospitality and computing facilities. J.B. acknowledges support from the CONICYT-Chile grant Basal-CATAPFB-06/2007 and FONDECYT Postdoctorados 3160439. R.S.-R. acknowledges support from ASI (Italian Space Agency) through the contract No. 2015-046-R.0 and from European Union Horizon 2020 Programme under the AHEAD project (grant agreement No. 654215). S.S. acknowledges support from the Feinberg Graduate School.

We present the extensive follow-up campaign on the afterglow of GRB 110715A at 17 different wavelengths, from X-ray to radio bands, starting 81 s after the burst and extending up to 74 d later. We performed for the first time a GRB afterglow observation with the ALMA observatory. We find that the afterglow of GRB 110715A is very bright at optical and radio wavelengths. We use the optical and near-infrared spectroscopy to provide further information about the progenitor's environment and its host galaxy. The spectrum shows weak absorption features at a redshift z = 0.8225, which reveal a host-galaxy environment with low ionization, column density, and dynamical activity. Late deep imaging shows a very faint galaxy, consistent with the spectroscopic results. The broad-band afterglow emission is modelled with synchrotron radiation using a numerical algorithm and we determine the best-fitting parameters using Bayesian inference in order to constrain the physical parameters of the jet and the medium in which the relativistic shock propagates. We fitted our data with a variety of models, including different density profiles and energy injections. Although the general behaviour can be roughly described by these models, none of them are able to fully explain all data points simultaneously. GRB 110715A shows the complexity of reproducing extensive multiwavelength broad-band afterglow observations, and the need of good sampling in wavelength and time and more complex models to accurately constrain the physics of GRB afterglows. ; RSR is grateful to SEPE for financial support while finishing this work and his PhD thesis. RSR, SRO, AJCT, YDH, SJ, and JCT acknowledge the financial support of the Spanish Government projects AYA 2009- 14000-C03-01 and AYA 2012-39727-C03-01. Parts of this research were conducted by the Australian Research Council Centre of Excellence for All-sky Astrophysics (CAASTRO), through project No. CE110001020. AdUP and CT acknowledge support from Ramon´ y Cajal fellowships and from the Spanish research project AYA 2014-58381. JJ acknowledges financial contribution from the grant PRIN MIUR 2012 201278X4FL 002 'The Intergalactic Medium as a probe of the growth of cosmic structures'. DAK acknowledges the financial support by MPE Garching and TLS Tautenburg. Part of the funding for GROND (both hardware as well as personnel) was generously granted from the Leibniz-Prize to Prof. G. Hasinger (DFG grant HA 1850/28-1). PS and TK acknowledges support through the Sofja Kovalevskaja Award to P. Schady from the Alexander von Humboldt Foundation of Germany. AU is grateful for travel funding support through the Max-Planck Inst. for Extraterrestrial Physics. SK and ANG acknowledge support by DFG grant Kl 766/16-1. This work made use of data supplied by the UK Swift Science Data Centre at the University of Leicester. Facilities: This publication is based on data acquired with the Atacama Pathfinder Experiment (APEX) under program 087.F- 9301(A). This paper makes use of the following ALMA data: ADS/JAO.ALMA#2011.0.00001.E. ALMA is a partnership of ESO (representing its member states), NSF (USA) and NINS (Japan), together with NRC (Canada), NSC and ASIAA (Taiwan), and KASI (Republic of Korea), in cooperation with the Republic of Chile. The Joint ALMA Observatory is operated by ESO, AUI/NRAO and NAOJ. This publication is based on data acquired with the VLT/Xshooter under program 087.A-0055(C), as well as with VLT/FORS2 under program 091.A-0703(A). ; Peer-reviewed ; Publisher Version

We have gathered optical photometry data from the literature on a large sample of Swift-era gamma-ray burst (GRB) afterglows including GRBs up to 2009 September, for a total of 76 GRBs, and present an additional three pre-Swift GRBs not included in an earlier sample. Furthermore, we publish 840 additional new photometry data points on a total of 42 GRB afterglows, including large data sets for GRBs 050319, 050408, 050802, 050820A, 050922C, 060418, 080413A, and 080810. We analyzed the light curves of all GRBs in the sample and derived spectral energy distributions for the sample with the best data quality, allowing us to estimate the host-galaxy extinction. We transformed the afterglow light curves into an extinction-corrected z = 1 system and compared their luminosities with a sample of pre-Swift afterglows. The results of a former study, which showed that GRB afterglows clustered and exhibited a bimodal distribution in luminosity space, are weakened by the larger sample. We found that the luminosity distribution of the two afterglow samples (Swift-era and pre-Swift) is very similar, and that a subsample for which we were not able to estimate the extinction, which is fainter than the main sample, can be explained by assuming a moderate amount of line-of-sight host extinction. We derived bolometric isotropic energies for all GRBs in our sample, and found only a tentative correlation between the prompt energy release and the optical afterglow luminosity at 1 day after the GRB in the z = 1 system. A comparative study of the optical luminosities of GRB afterglows with echelle spectra (which show a high number of foreground absorbing systems) and those without, reveals no indication that the former are statistically significantly more luminous. Furthermore, we propose the existence of an upper ceiling on afterglow luminosities and study the luminosity distribution at early times, which was not accessible before the advent of the Swift satellite. Most GRBs feature afterglows that are dominated by the forward shock from early times on. Finally, we present the first indications of a class of long GRBs, which form a bridge between the typical high-luminosity, high-redshift events and nearby low-luminosity events (which are also associated with spectroscopic supernovae) in terms of energetics and observed redshift distribution, indicating a continuous distribution overall. ; DFG Kl 766/13-2 ; NASA NNG 05GC22G, NNG06GH62G ; Spanish research programs ESP2005-07714-C03-03, AYA2004-01515 ; Instrument Center for Danish Astrophysics ; Danish National Science Fundation G2007101421517916 ; CRDF RP1-2394-MO-02 ; TUBITAK ; IKI ; KSU RTT150, 998,999 ; Korea government (MEST) 2010-0000712 ; NSh-4224.2008.2 ; RFBR-09-02-97013-p-povolzh'e-a ; Astronomy