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GCN Circular 20384

LIGO/Virgo G268556: HAWC follow-up of northern sky
2017-01-06T20:34:07Z (7 years ago)
Joshua Wood at UW-Madison <>
J. Wood (UW-Madison) and I. Martinez (UMD)
report on behalf of the HAWC Collaboration:

The northern portion of the reported LIGO error region was within the HAWC field-of-view at the time of LVC trigger G268556. HAWC was operating and our real-time all-sky GRB monitoring analysis was running at this time. This analysis searches for excess counts over the steady-state cosmic-ray background using 4 sliding time windows (0.1, 1, 10, and 100 seconds) shifted forward in time by 10% their width over the course of the entire day. Within each time window, we search the HAWC sky within 50 degrees of zenith using 2.1 deg x 2.1 deg square bins shifted by ~0.1 deg along the directions of Right Ascension and Declination. This analysis is tuned for detecting ~100 GeV photons and is sensitive to the most fluent GRBs. It did not report any significant post-trials events near the time of gravitational-wave trigger G268556.

On 2017/01/05 we went back and re-analyzed the data within +/- 60 seconds of gravitational-wave trigger G268556 on 3 timescales (1, 10, 100 sec) to look for excesses consistent with the latest LIGO map. None were found.

As a complementary analysis we integrated the ~2 hours following the trigger time. This corresponds to the time interval when the searched region (90% probability contour) stayed in our field-of-view. The analysis performed on this data set is sensitive to ~0.5-100TeV. We found no significant excess.

HAWC is a TeV gamma ray water Cherenkov array located in the state of Puebla, Mexico that monitors 2/3 of the sky every day with an instantaneous field of view of ~2 sr.
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