TITLE: GCN CIRCULAR NUMBER: 21683 SUBJECT: LIGO/Virgo G298048: HAWC follow-up DATE: 17/08/24 19:35:19 GMT FROM: Israel Martinez-Castellanos at UMD/HAWC I. Martinez-Castellanos (University of Maryland, College Park) and A.J. Smith (University of Maryland, College Park) on behalf of the HAWC Collaboration: HAWC Collaboration performed a follow-up of LIGO trigger G298048. At the time of the trigger no portion of the LV contour was visible to HAWC, so no prompt follow-up was possible. About 9hrs after the trigger the LV region transited through the HAWC FOV (95% of the probability was covered), albeit with a large zenith angle, which limits the sensitivity of our observations. There were no >5 sigma points observed during this transit. For a single transit, the 5 sigma sensitivity to a power law spectrum with a -2.5 index ranges from ~2e-11 >1TeV cm^-2 s^-1 (~3 Crab units) at dec=-12 to about 6 times higher at the edge of our FOV, dec=-25. At the point of the optical counterpart candidate SSS17a/DLT17ck (RA=13:09:48.09 DEC=-23:22:53.35) reported by Coulter et al. (LVC GCN 21529), Allam et al. (LVC GCN 21530), Yang et al. (LVC GCN 21531), Melandri et al. (LVC GCN 21532), we obtain an 95% confidence level upper limit for >1TeV assuming a -2.5 spectrum of 1.0e-10 cm^-2 s^-1. These observations were made on 2017-08-17 between 19:57 UT and 23:25 UT with culmination 9:00 hrs after the LV trigger. HAWC is a TeV gamma ray water Cherenkov array located in the state of Puebla, Mexico. It is sensitive to the energy range ~0.5-100TeV, and monitors 2/3 of the sky every day with an instantaneous field-of-view of ~2 sr.