University of Leicester
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The luminous host galaxy, faint supernova and rapid afterglow rebrightening of GRB 100418A

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posted on 2019-02-06, 15:50 authored by ADU Postigo, CC Thone, K Bensch, AJ van der Horst, DA Kann, Z Cano, L Izzo, P Goldoni, S Martin, R Filgas, P Schady, J Gorosabel, I Bikmaev, M Bremer, R Burenin, AJ Castro-Tirado, S Covino, JPU Fynbo, D Garcia-Appadoo, I de Gregorio-Monsalvo, M Jelinek, I Khamitov, A Kamble, C Kouveliotou, T Kruehler, G Leloudas, S Melnikov, M Nardini, DA Perley, G Petitpas, G Pooley, A Rau, E Rol, R Sanchez-Ramirez, RLC Starling, NR Tanvir, K Wiersema, RAMJ Wijers, T Zafar
Context. Long gamma-ray bursts (GRBs) give us the chance to study both their extreme physics and the star-forming galaxies in which they form. Aims. GRB 100418A, at a redshift of z = 0.6239, had a bright optical and radio afterglow, and a luminous star-forming host galaxy. This allowed us to study the radiation of the explosion as well as the interstellar medium of the host both in absorption and emission. Methods. We collected photometric data from radio to X-ray wavelengths to study the evolution of the afterglow and the contribution of a possible supernova (SN) and three X-shooter spectra obtained during the first 60 h. Results. The light curve shows a very fast optical rebrightening, with an amplitude of ∼3 magnitudes, starting 2.4 h after the GRB onset. This cannot be explained by a standard external shock model and requires other contributions, such as late central-engine activity. Two weeks after the burst we detect an excess in the light curve consistent with a SN with peak absolute magnitude MV = −18.5 mag, among the faintest GRBSNe detected to date. The host galaxy shows two components in emission, with velocities differing by 130 km s−1 , but otherwise having similar properties. While some absorption and emission components coincide, the absorbing gas spans much higher velocities, indicating the presence of gas beyond the star-forming regions. The host has a star formation rate of SFR = 12.2 M yr−1 , a metallicity of 12 + log(O/H) = 8.55, and a mass of 1.6 × 109 M . Conclusions. GRB 100418A is a member of a class of afterglow light curves which show a steep rebrightening in the optical during the first day, which cannot be explained by traditional models. Its very faint associated SN shows that GRB-SNe can have a larger dispersion in luminosities than previously seen. Furthermore, we have obtained a complete view of the host of GRB 100418A owing to its spectrum, which contains a remarkable number of both emission and absorption lines.


AdUP, CCT, KB, DAK, LI, and ZC acknowledge support from the Spanish Ministry of Economy and Competitivity under grant number AYA 2014-58381-P; in addition, AdUP and CCT from Ramón y Cajal fellowships (RyC-2012-09975 and RyC-2012-09984). DAK also acknowledges financial support from Juan de la Cierva Incorporación fellowship IJCI-2015-26153. RF acknowledges support from European Regional Development Fund-Project “Engineering applications of microworld physics” (No. CZ.02.1.01/0.0/0.0/16_019/0000766). IB, IKh, RB, and SM acknowledge TUBITAK, IKI, KFU, and AST for partial support in using RTT150. This work was partially funded by the subsidy 3.6714.2017/8.9 allocated to Kazan Federal University for the state assignment in the sphere of scientific activities. TK acknowledges support from the DFG cluster of excellence “Origin and Structure of the Universe”. PS acknowledges support through the Sofja Kovalevskaja Award from the Alexander von Humboldt Foundation of Germany. RSR acknwoledges support from ASI (Italian Space Agency) through Contract n. 2015- 046-R.0 and from European Union Horizon 2020 Programme under the AHEAD project (grant agreement n. 654215). The Cosmic Dawn Center is funded by the DNRF. Based on observations made with the Gran Telescopio Canarias (GTC), installed in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de Canarias, in the island of La Palma. The Submillimeter Array is a joint project between the Smithsonian Astrophysical Observatory and the Academia Sinica Institute of Astronomy and Astrophysics and is funded by the Smithsonian Institution and the Academia Sinica. This work is based on observations carried out under project number U051 with the IRAM Plateau de Bure Interferometer. IRAM is supported by INSU/CNRS (France), MPG (Germany), and IGN (Spain). Some of the data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the Cali



Astronomy and Astrophysics, 2018, 620, pp. ?-? (23)

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