Challenging the Forward Shock Model with the 80 Ms Follow up of the X-ray Afterglow of Gamma-Ray Burst 130427A

GRB 130427A was the most luminous gamma-ray burst detected in the last 30 years. With an isotropic energy output of 8.5 x 10(53) erg and redshift of 0.34, it combined very high energetics with a relative proximity to Earth in an unprecedented way. Sensitive X-ray observatories such as XMM-Newton and Chandra have detected the afterglow of this event for a record-breaking baseline longer than 80 million seconds. The light curve displays a simple power-law over more than three decades in time. In this presentation, we explore the consequences of this result for a few models put forward so far to interpret GRB 130427A, and more in general the implication of this outcome in the context of the standard forward shock model.M.D.P. and M.J.P. thank the UK Space Agency for support. A.R. thanks support from PRIN-INAF 2012/13 and from Premiale LBT 2013. B.G. recognizes financial support of the NASA through the NASA Award NNX13AD28A and the NASA Award NNX15AP95A. Part of this work is under the auspice of the FIGARONet collaborative network, supported by the Agence Nationale de la Recherche, program ANR-14-CE33. D.A.K. acknowledges support by TLS Tautenburg, as a research stipend. D.M. thanks the support of Ida as well as financial support from Instrument Center for Danish Astrophysics (IDA). G.S. acknowledges the financial support, through grant FIRB 2012 RBFR12PM1F, provided by the Italian Ministry of Education, University and Research (MIUR). S.R.O. acknowledges the support provided by the Spanish Ministry, Project Number AYA2012-39727-C03-01, and acknowledges the support of the Leverhulme Trust. Z.C. gratefully acknowledges financial support provided by the Icelandic Research Fund (IRF). This work made use of data supplied by the UK Swift Science Data Centre at the University of Leicester, and by the Chandra Data Archive.Peer Reviewe