Browsing by Subject "stars: flare"

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Discovery Of A Cosmological, Relativistic Outburst Via Its Rapidly Fading Optical Emission
(2013-06) Cenko, S. Bradley; Kulkarni, S. R.; Horesh, Assaf; Corsi, Alessandra; Fox, Derek B.; Carpenter, John; Frail, Dale A.; Nugent, Peter E.; Perley, Daniel A.; Gruber, D.; Gal-Yam, Avishay; Groot, Paul J.; 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; Silverman, Jeffrey M.
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.
Revealing The Millimeter Environment Of The New FU Orionis Candidate HBC722 With The Submillimeter Array
(2012-08) Dunham, Michael M.; Arce, Hector G.; Bourke, Tyler L.; Chen, Xuepeng; van Kempen, Tim A.; Green, Joel D.; Green, Joel D.
We present 230 GHz Submillimeter Array continuum and molecular line observations of the newly discovered FU Orionis candidate HBC722. We report the detection of seven 1.3 mm continuum sources in the vicinity of HBC722, none of which corresponds to HBC722 itself. We compile infrared and submillimeter continuum photometry of each source from previous studies and conclude that three are Class 0 embedded protostars, one is a Class I embedded protostar, one is a Class I/II transition object, and two are either starless cores or very young, very low luminosity protostars or first hydrostatic cores. We detect a northwest-southeast outflow, consistent with the previous detection of such an outflow in low-resolution, single-dish observations, and note that its axis may be precessing. We show that this outflow is centered on and driven by one of the nearby Class 0 sources rather than HBC722, and find no conclusive evidence that HBC722 itself is driving an outflow. The non-detection of HBC722 in the 1.3 mm continuum observations suggests an upper limit of 0.02 M-circle dot for the mass of the circumstellar disk. This limit is consistent with typical T Tauri disks and with a disk that provides sufficient mass to power the burst.