LIGO/Virgo G288732: IceCube neutrino observations update

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>; for more information on joint neutrino and gravitational wave searches, please refer to<http://adsabs.harvard.edu/cgi-bin/bib_query?arXiv:1602.05411>.