Article

Hypernova Signatures in the Late Rebrightening of GRB 050525A

M. Della ValleKavli Institute for Theoretical Physics, University of California, Santa Barbara, CA 93106-4030D. MalesaniInternational School for Advanced Studies, via Beirut 2-4, I-34014 Trieste, ItalyJ. S. BloomDepartment of Astronomy, University of California at Berkeley, 601 Campbell Hall, Berkeley, CA 94720S. BenettiIstituto Nazionale di Astrofisica/Osservatorio Astronomico di Padova, Vicolo dell'Osservatorio 5, I-35122 Padova, ItalyG. ChincariniIstituto Nazionale di Astrofisica/Osservatorio Astronomico di Brera, Via E. Bianchi 46, I-23807 Merate (LC), ItalyP. D’AvanzoIstituto Nazionale di Astrofisica/Osservatorio Astronomico di Brera, Via E. Bianchi 46, I-23807 Merate (LC), ItalyR. J. FoleyDepartment of Astronomy, University of California at Berkeley, 601 Campbell Hall, Berkeley, CA 94720S. CovinoIstituto Nazionale di Astrofisica/Osservatorio Astronomico di Brera, Via E. Bianchi 46, I-23807 Merate (LC), ItalyA. MelandriAstrophysics Research Institute, John Moores University, 12 Quays House, Egerton Wharf, Birkenhead CH41, UKS. PiranomonteIstituto Nazionale di Astrofisica/Osservatorio Astronomico di Roma, via di Frascati 33, I-00040 Monteporzio Catone (Roma), ItalyG. TagliaferriIstituto Nazionale di Astrofisica/Osservatorio Astronomico di Brera, Via E. Bianchi 46, I-23807 Merate (LC), ItalyL. StellaIstituto Nazionale di Astrofisica/Osservatorio Astronomico di Roma, via di Frascati 33, I-00040 Monteporzio Catone (Roma), ItalyR. GilmozziEuropean Southern Observatory, Karl-Schwarzschild-Strasse 2, D-85748 Garching bei Munchen, GermanyL. A. AntonelliIstituto Nazionale di Astrofisica/Osservatorio Astronomico di Roma, via di Frascati 33, I-00040 Monteporzio Catone (Roma), ItalyS. CampanaIstituto Nazionale di Astrofisica/Osservatorio Astronomico di Brera, Via E. Bianchi 46, I-23807 Merate (LC), ItalyChen, H. W.Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology, Cambridge, MA 02139-4307P. FilliatreLaboratoire Astroparticule et Cosmologie, UMR 7164, 11 Place Marcelin Berthelot, F-75231 Paris Cedex 05, FranceF. FioreAstrophysics Research Institute, John Moores University, 12 Quays House, Egerton Wharf, Birkenhead CH41, UKD. FugazzaIstituto Nazionale di Astrofisica/Osservatorio Astronomico di Brera, Via E. Bianchi 46, I-23807 Merate (LC), ItalyN. GehrelsNASA Goddard Space Flight Center, Greenbelt, MD 20771K. HurleySpace Sciences Laboratory, University of California at Berkeley, 601 Campbell Hall, Berkeley, CA 94720-7450Mirabel Miquele, Igor FelixEuropean Southern Observatory, Alonso de Córdova 3107, Vitacura, Casilla 19001, Santiago 19, ChilePellizza González, Leonardo JavierAIM (UMR 7158 CEA/CNRS/Université Paris 7), Service d'Astrophysique, CEA Saclay, F-91191 Gif-sur-Yvette Cedex, FranceL. PiroInstituto Nazionale di Astrofisica/IASF Sezione di Roma, Via del Fosso del Cavaliere 100, I-00113 Roma, ItalyJ. X. ProchaskaLick Observatory, University of California at Santa Cruz, 373 Interdisciplinary Sciences, Santa Cruz, CA 95064

2006en

ABI

Abstract

We report observations of GRB 050525A, for which a Gemini North spectrum shows its redshift to be z=0.606. This is the third closest long GRB discovered by Swift. We observed its afterglow using the VLT, Gemini, and TNG telescopes to search for an associated supernova. We find that the early-time light curve is described by a broken power law with a break at t~0.3 days after the burst. About 5 days after the burst, a flattening is apparent, followed by a further dimming. Both the magnitude and the shape of the light curve suggest that a supernova was emerging during the late decay of the afterglow. This supernova, named SN 2005nc, had a rise time faster than SN 1998bw and a long-lasting maximum. A spectrum obtained about 20 days (rest frame) after the GRB resembles the spectrum of SN 1998bw obtained close to maximum light.

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