DISCOVERY OF A COSMOLOGICAL, RELATIVISTIC OUTBURST VIA ITS RAPIDLY FADING OPTICAL EMISSION
Author(s)Cenko, S. Bradley; Kulkarni, S. R.; Horesh, Assaf; Corsi, A.; Fox, Derek B.; Carpenter, John; Frail, Dale A.; Nugent, Peter E.; Perley, Daniel A.; Gruber, D.; Gal-Yam, Avishay; Groot, P.; Hallinan, G.; Ofek, Eran O.; Rau, Arne; MacLeod, Chelsea L.; Miller, Adam A.; Bloom, Joshua S.; Filippenko, Alexei V.; Kasliwal, Mansi M.; Law, Nicholas M.; Morgan, Adam N.; Polishook, David; Poznanski, Dovi; Quimby, Robert M.; Sesar, Branimir; Shen, Ken J.; Silverman, Jeffrey M.; Sternberg, Assaf; ... Show more Show less
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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[subscript 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.
DepartmentMassachusetts Institute of Technology. Department of Earth, Atmospheric, and Planetary Sciences
Institute of Physics/American Astronomical Society
Cenko, S. Bradley, S. R. Kulkarni, Assaf Horesh, Alessandra Corsi, Derek B. Fox, John Carpenter, Dale A. Frail, et al. “DISCOVERY OF A COSMOLOGICAL, RELATIVISTIC OUTBURST VIA ITS RAPIDLY FADING OPTICAL EMISSION.” The Astrophysical Journal 769, no. 2 (May 14, 2013): 130. © 2013 American Astronomical Society.
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