Discovery of a Cosmological, Relativistic Outburst via its Rapidly Fading Optical Emission

Creators: Cenko, S. Bradley; Kulkarni, S. R.; Horesh, Assaf; Corsi, Alessandra; Carpenter, John; Perley, Daniel A.; Groot, Paul J.; Hallinan, G.; Sesar, Branimir; Kasliwal, M. M.

Abstract

We report the discovery by the Palomar Transient Factory (PTF) of the transient source PTF11agg, which is distinguished by three primary characteristics: (1) bright (R_peak = 18.3 mag), rapidly fading (ΔR = 4 mag in Δt = 2 days) optical transient emission; (2) a faint (R = 26.2 ± 0.2 mag), blue (g' – R = 0.17 ± 0.29 mag) quiescent optical counterpart; and (3) an associated year-long, scintillating radio transient. We argue that these observed properties are inconsistent with any known class of Galactic transients (flare stars, X-ray binaries, dwarf novae), and instead suggest a cosmological origin. The detection of incoherent radio emission at such distances implies a large emitting region, from which we infer the presence of relativistic ejecta. The observed properties are all consistent with the population of long-duration gamma-ray bursts (GRBs), marking the first time such an outburst has been discovered in the distant universe independent of a high-energy trigger. We searched for possible high-energy counterparts to PTF11agg, but found no evidence for associated prompt emission. We therefore consider three possible scenarios to account for a GRB-like afterglow without a high-energy counterpart: an "untriggered" GRB (lack of satellite coverage), an "orphan" afterglow (viewing-angle effects), and a "dirty fireball" (suppressed high-energy emission). The observed optical and radio light curves appear inconsistent with even the most basic predictions for off-axis afterglow models. The simplest explanation, then, is that PTF11agg is a normal, on-axis long-duration GRB for which the associated high-energy emission was simply missed. However, we have calculated the likelihood of such a serendipitous discovery by PTF and find that it is quite small (≈2.6%). While not definitive, we nonetheless speculate that PTF11agg may represent a new, more common (>4 times the on-axis GRB rate at 90% confidence) class of relativistic outbursts lacking associated high-energy emission. If so, such sources will be uncovered in large numbers by future wide-field optical and radio transient surveys.

Additional Information

© 2013 American Astronomical Society. Received 2013 January 20; accepted 2013 April 15; published 2013 May 14. We thank David Levitan and Kunal Mooley for obtaining observations used in this work, and John Tomsick for valuable comments on the manuscript. We are grateful to the following IPN team members for sharing their data: K. Hurley, I. G. Mitrofanov, D. Golovin, M. L. Litvak, A. B. Sanin,W. Boynton, C. Fellows, K. Harshman, R. Starr, S. Golenetskii, R. Aptekar, E. Mazets, V. Pal'shin, D. Frederiks, D. Svinkin, A. von Kienlin, X. Zhang, K. Yamaoka, T. Takahashi, M. Ohno, Y. Hanabata, Y. Fukazawa,M. Tashiro, Y. Terada, T. Murakami, K. Makishima, T. Cline, S. Barthelmy, J.Cummings,N.Gehrels, H. Krimm, D. Palmer, J. Goldsten, V. Connaughton, M. S. Briggs, and C. Meegan. A.V.F. and his group acknowledge generous financial assistance from Gary and Cynthia Bengier, the Richard and Rhoda Goldman Fund, the Christopher R. Redlich Fund, NASA/Swift grants NNX10AI21G and NNX12AD73G, the TABASGO Foundation, and NSF grant AST-1211916. A.C. acknowledges support from LIGO, which was constructed by the California Institute of Technology and theMassachusetts Institute of Technology with funding from the NSF and operates under cooperative agreement PHY-0757058. D.A.P. is supported by NASA through Hubble Fellowship grantHST-HF-51296.01-A awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., for NASA, under contract NAS 5-26555. Research by A.G.Y. and his team is supported by grants from the ISF, BSF, GIF, the EU/FP7 via an ERC grant, and a Kimmel Award. P.J.G. acknowledges support from Caltech during his 2011 sabbatical stay. E.O.O. is incumbent of the Arye Dissentshik career development chair and is grateful to support by a grant from the Israeli Ministry of Science. A.A.M. is supported by the NSF Graduate Research Fellowship Program. J.S.B. acknowledges NSF grant CDI-0941742. D.P. is grateful for the AXA research fund. A.S. is supported by a Minerva Fellowship. M.M.K. acknowledges generous support from the Hubble Fellowship and Carnegie-Princeton Fellowship. Observations were obtained with the Samuel Oschin telescope and the Hale telescope at Palomar Observatory as part of the Palomar Transient Factory project, a scientific collaboration between the California Institute of Technology, Columbia University, Las Cumbres Observatory, the Lawrence Berkeley National Laboratory, the National Energy Research Scientific Computing Center, the University of Oxford, and theWeizmann Institute of Science. The National Energy Research Scientific Computing Center, supported by the Office of Science of the U.S. Department of Energy, provided staff, computational resources, and data storage for this project. Support for CARMA construction was derived from the Gordon and Betty Moore Foundation, the Kenneth T. and Eileen L. Norris Foundation, the James S. McDonnell Foundation, the Associates of the California Institute of Technology, the University of Chicago, the states of California, Illinois, and Maryland, and the NSF. Ongoing CARMA development and operations are supported by the NSF under a cooperative agreement, and by the CARMA partner universities. 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 NASA; the Observatory was made possible by the generous financial support of the W. M. Keck Foundation. PAIRITEL is operated by the Smithsonian Astrophysical Observatory (SAO) and was made possible by a grant from the Harvard University Milton Fund, a camera loan from the University of Virginia, and continued support of the SAO and UC Berkeley. The PAIRITEL project is further supported by NASA/Swift Guest Investigator grant NNX08AN84G. This work made use of data supplied by the UK Swift Science Data Centre at the University of Leicester. It also made use of the NASA/IPAC Extragalactic Database (NED), which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with NASA. In addition, we have utilized the SIMBAD database, operated at CDS, Strasbourg, France. Facilities: PO:1.2m (PTF), Hale (WIRC), Keck:I (LRIS), Magellan:Baade (IMACS), FLWO:2MASS (PAIRITEL), VLA, CARMA, Fermi (GBM), Swift (BAT, XRT)

Attached Files

Published - 0004-637X_769_2_130.pdf

Submitted - 1304.4236.pdf

Files

1304.4236.pdf

Files (1.9 MB)

Name	Size	Download all
1304.4236.pdf md5:cab6ac24a5400340c4363c60f3ffe16f	823.3 kB	Preview Download
0004-637X_769_2_130.pdf md5:f24c615b8f3372b683a0e5e40d1ec17a	1.1 MB	Preview Download

Additional details

	All versions	This version
Views	0	0
Downloads	0	0
Data volume	0 Bytes	0 Bytes