Journal
ASTROPHYSICAL JOURNAL
Volume 769, Issue 2, Pages -Publisher
IOP PUBLISHING LTD
DOI: 10.1088/0004-637X/769/2/130
Keywords
gamma-ray burst: general; stars: flare; supernovae: general
Categories
Funding
- Gary and Cynthia Bengier
- Richard and Rhoda Goldman Fund
- Christopher R. Redlich Fund
- NASA/Swift [NNX10AI21G, NNX12AD73G]
- TABASGO Foundation
- NSF [AST-1211916, PHY-0757058, CDI-0941742]
- LIGO
- Massachusetts Institute of Technology
- NASA [HST-HF-51296.01-A, NAS 5-26555]
- Space Telescope Science Institute
- ISF
- BSF
- GIF
- EU/FP7 via an ERC
- Kimmel Award
- Caltech
- Israeli Ministry of Science
- NSF Graduate Research Fellowship Program
- Minerva Fellowship
- Hubble Fellowship
- Carnegie-Princeton Fellowship
- Direct For Mathematical & Physical Scien
- Division Of Astronomical Sciences [1139950, 1140063, 1302771, 1139998] Funding Source: National Science Foundation
- Division Of Astronomical Sciences
- Direct For Mathematical & Physical Scien [1140031, 1211916, 1140019, 1009987] Funding Source: National Science Foundation
- Office of Integrative Activities [0941742] Funding Source: National Science Foundation
- Office Of The Director [0941742] Funding Source: National Science Foundation
- NASA [53354, NNX12AD73G] Funding Source: Federal RePORTER
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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-peak = 18.3mag), rapidly fading (Delta R = 4mag in Delta t = 2 days) optical transient emission; (2) a faint (R = 26.2 +/- 0.2mag), 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 (approximate to 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.
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