Archival ASKAP observations of the candidate counterpart to IceCube-211116A

ATel #15049; Dougal Dobie (Swinburne/OzGrav), David L. Kaplan (UWM), Gregory R. Sivakoff (University of Alberta), Ziteng Wang (University of Sydney), Adam Stewart (University of Sydney), Andrew O’Brien (UWM)
on 19 Nov 2021; 09:53 UT
Credential Certification: Dougal Dobie (ddob1600@uni.sydney.edu.au)

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Kovalev et al. (ATel#15046) have recently proposed the blazar 0250-001 as a candidate source of the neutrino event IceCube-211116A (GCN #31091). This Bronze Alert (30-50% astrophysical purity) had an estimated false alarm rate from atmospheric backgrounds of 1.9 events per year.

We have previously observed 0250-001 with the Australian Square Kilometre Array Pathfinder as part of the Variables and Slow Transients pilot survey (Murphy et al. 2021, PASA, 38, e054), with semi-regular monitoring spanning nearly 2.5 years. All observations were carried out with 288 MHz of bandwidth centered on 888 MHz. We report the following flux density measurements:

 
       Observation Date  Peak Flux Density (mJy/beam)  Uncertainty (mJy/beam) 
2019-04-26 03:58:27.235                         137.9                     0.3 
2019-08-27 16:44:16.531                         117.9                     0.1 
2019-10-28 15:15:42.475                         127.6                     0.2 
2019-12-19 13:15:05.445                         111.9                     0.2 
2020-01-10 11:57:30.296                         125.8                     0.2 
2020-01-11 11:53:55.747                         123.9                     0.1 
2020-01-16 12:00:29.897                         107.8                     0.1 
2020-01-17 11:17:47.149                         115.8                     0.1 
2020-01-17 11:45:29.346                         111.0                     0.1 
2020-01-18 11:11:33.348                         105.5                     0.1 
2020-01-18 11:41:34.891                         106.8                     0.2 
2020-06-19 23:40:30.527                         159.4                     0.1 
2020-08-28 19:05:37.942                         132.5                     0.2 
2021-07-21 22:51:01.906                         169.3                     0.3 
2021-08-21 19:49:41.975                         179.6                     0.3 

The corresponding variability metrics are eta=16500, V=0.18, indicating a moderately variable source. There is no evidence for any previous strong outbursts in the lightcurve, although we note that all our observations occurred more than 86 days before the neutrino event. We also note that our last two observations were the brightest flux densities, which could be consistent with neutrino activity that is tied to the time-integrated neutrino flux as opposed to a more impulsive flare. However, given the astrophysical purity of this event and the uncalculated number of potential other sources showing a similar behaviour at radio frequencies, we cannot confidently attribute the recently measured increased flux to the neutrino event.

This work was done as part of the ASKAP Variables and Slow Transients (VAST) collaboration (Murphy et al. 2013, PASA, 30, 6).

The Australian SKA Pathfinder is part of the Australia Telescope National Facility which is managed by CSIRO. Operation of ASKAP is funded by the Australian Government with support from the National Collaborative Research Infrastructure Strategy. ASKAP uses the resources of the Pawsey Supercomputing Centre. Establishment of ASKAP, the Murchison Radio-astronomy Observatory and the Pawsey Supercomputing Centre are initiatives of the Australian Government, with support from the Government of Western Australia and the Science and Industry Endowment Fund. We acknowledge the Wajarri Yamatji people as the traditional owners of the Observatory site.

ASKAP lightcurve