Happy Birthday Swift: Ultra-Long GRB 141121A and its Broadband Afterglow

Creators: Cucchiara, A.; Perley, D. A.; Horesh, A.

Abstract

We present our extensive observational campaign on the Swift-discovered GRB 141121A, almost 10 years after its launch. Our observations cover radio through X-rays and extend for more than 30 days after discovery. The prompt phase of GRB 141121A lasted 1410 s and, at the derived redshift of z = 1.469, the isotropic energy is E_(γ,iso) = 8.0 × 10^(52) erg. Due to the long prompt duration, GRB 141121A falls into the recently discovered class of ultra-long GRBs (UL-GRBs). Peculiar features of this burst are (1) a flat early-time optical light curve and (2) a radio-to-X-ray rebrightening around three days after the burst. The latter is followed by a steep optical-to-X-ray decay and a much shallower radio fading. We analyze GRB 141121A in the context of the standard forward–reverse shock (FS, RS) scenario and we disentangle the FS and RS contributions. Finally, we comment on the puzzling early-time (t ≾ 3 days) behavior of GRB 141121A, and suggest that its interpretation may require a two-component jet model. Overall, our analysis confirms that the class of UL-GRBs represents our best opportunity to firmly establish the prominent emission mechanisms in action during powerful gamma-ray burst explosions, and future missions (like SVOM, XTiDE, or ISS-Lobster) will provide many more of such objects.

Additional Information

© 2015 American Astronomical Society. Received 2015 May 31; accepted 2015 August 6; published 2015 October 15. This research was supported by the NASA Postdoctoral Program at the Goddard Space Flight Center, administered by Oak Ridge Associated Universities through a contract with NASA. A.C. thanks the PI of the Keck observations (Christian Ott) and the observers (Maryam Modjaz and David Fierroz) for donating some of their precious time to observe GRB 141121A. A.C. also acknowledges partial support from the NASA-Swift GI program via grants 13-SWIFT13-0030 and 14-SWIFT14-0024. Partial support of OTKA NN 111016 grant (PV). S.B.C. acknowledges support from the NASA Fermi grant NNH13ZDA001N. Partial support for DAP was provided by NASA through an award issued by JPL/Caltech. This work made use of data supplied by the UK Swift Science Data Centre at the University of Leicester. We thank the CARMA observers (in particular, G. Keating) for executing our observations. Some of the data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. We thank the RATIR project team and the staff of the Observatorio Astronmico Nacional on Sierra San Pedro Mrtir. RATIR is a collaboration between the University of California, the Universidad Nacional Autónoma de México, NASA Goddard Space Flight Center, and Arizona State University, benefiting from the loan of an H2RG detector and hardware and software support from Teledyne Scientific and Imaging. RATIR, the automation of the Harold L. Johnson Telescope of the Observatorio Astronmico Nacional on Sierra San Pedro Mrtir, and the operation of both are funded through NASA grants NNX09AH71G, NNX09AT02G, NNX10AI27G, and NNX12AE66G, CONACyT grants INFR-2009-01-122785 and CB-2008-101958, UNAM PAPIIT grant IN113810, IG100414, and UC MEXUS-CONACyT grant CN 09-283. M. Modjaz is supported, in part, by the NSF CAREER award AST-1352405 and by the NSF award AST-1413260. These results made use of the Lowell Observatory Discovery Channel Telescope. Lowell operates the DCT in partnership with Boston University, Northern Arizona University, the University of Maryland, and the University of Toledo. Partial support of the DCT was provided by Discovery Communications. LMI was built by Lowell Observatory using funds from the National Science Foundation (AST-1005313).

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