GCN Circular 21226

I. Bartos, S. Countryman (Columbia), C. Finley (U Stockholm), E. Blaufuss (U Maryland), R. Corley, Z. Marka, S. Marka (Columbia) on behalf of the IceCube Collaboration


We previously reported on the online track-like neutrino search for LIGO-Virgo trigger G288732. We are updating this result with adopting a new online configuration, which enables better background rejection online, allowing for an increased rate of events passing the neutrino track event selection, along a higher efficiency for neutrino events. With this online search, the expected background neutrino rate is ~6 within our [-500,500] time window.

----

We searched IceCube online track-like neutrino candidates (GFU) detected in a [-500,500] second interval about the LIGO-Virgo trigger G288732. We compared the candidate source directions of 7 temporally-coincident neutrinos to the BAYESTAR skymap, with the following parameters:

#            dt[s]     RA[deg]    Dec[deg]      E[TeV]  Sigma[deg]
------------------------------------------------------------------
1.         -106.97        28.5        23.7        1.03         1.2
2.          -97.96       252.1         8.0        0.90         1.8
3.          -67.26       299.0        28.6        1.38         1.4
4.          -44.07        99.0       -67.8      224.91         0.2
5.          331.13       269.8        43.7        1.09         5.7
6.          337.70       241.7        26.3        0.97         1.5
7.          462.61       310.9        -5.5        2.53         0.8


(dt--time from GW in [seconds]; RA/Dec--sky location in [degrees]; E--reconstructed secondary muon energy in [TeV]; Sigma--uncertainty of direction reconstruction in [degrees])

The analysis found NO COINCIDENT ONLINE TRACK-LIKE NEUTRINO CANDIDATES detected by IceCube within the 500 second window surrounding G288732 within the BAYESTAR skymap.

A coincident neutrino-GW skymap has been posted to GraceDB (<https://gracedb.ligo.org/apiweb/events/G288732/files/coinc_skymap_initial_icecube.png,2>). A JSON-formatted list of the above neutrinos can be downloaded from GraceDB at:<https://gracedb.ligo.org/apiweb/events/G288732/files/IceCubeNeutrinoList.json,3>

In addition, we are performing coincident searches with other IceCube data streams, including the high-energy starting events (HESE) and Supernova triggers.  HESE events have typical energies > 60 TeV and start inside the detector volume, leading to a relatively pure event sample with a high fraction of astrophysical neutrinos.  The SN trigger system is sensitive to sudden increases in photomultiplier counts across the detector, which could indicate a burst of MeV neutrinos.  We will submit separate GCN circulars if coincident HESE or SN triggers are found.

The IceCube Neutrino Observatory is a cubic-kilometer neutrino detector operating at the geographic South Pole, Antarctica.  For a description of the IceCube realtime alert system, please refer to<http://adsabs.harvard.edu/cgi-bin/bib_query?arXiv:1610.01814
Not found
 
 
>; for more information on joint neutrino and gravitational wave searches, please refer to<http://adsabs.harvard.edu/cgi-bin/bib_query?arXiv:1602.05411
Not found
 
 
>.