[vsnet-grb-info 22531] LIGO/Virgo S190521r: No counterpart candidates in HAWC observations

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  24630
SUBJECT: LIGO/Virgo S190521r: No counterpart candidates in HAWC observations
DATE:    19/05/21 08:20:47 GMT
FROM:    Hugo Ayala at Pennsylvania State University  <hgayala at psu.edu>

The HAWC Collaboration (https://www.hawc-observatory.org) reports:

The HAWC Collaboration performed a follow-up of the gravitational wave
trigger S190521r. At the time of the trigger the HAWC
local zenith was oriented towards (RA, Dec) = (257.1 deg, 19.0 deg).
72% of the GW candidate sky location probability fell within our
observable field of view (0-45 deg zenith angle).

We performed a search for a short timescale emission using 6 sliding
time windows (dt = 0.3s, 1s, 3s, 10s, 30s and  100s), shifted forward
in time by 20% of their width. We searched the 95% probability
containment area in a timescale-dependent time period, from t0-5dt to
t0+10dt, where t0 is the time of the GW trigger.

No significant gamma-ray detection above the background was observed.

The sensitivity of this analysis is greatly dependent on zenith angle,
ranging from 12.6 deg to 45.0 deg for the area searched in this
analysis. The 5sigma detection sensitivity to a 1s (100s) burst in the
80-800GeV energy range goes from 1.5e-06 erg/cm^2 to 1.1e-04 erg/cm^2
(8.0e-06 erg/cm^2 to 5.0e-04 erg/cm^2), depending on the zenith
angle.

HAWC is a TeV gamma ray water Cherenkov array located in the state of
Puebla, Mexico. It is sensitive to the energy range ~0.1-100TeV, and
monitors 2/3 of the sky every day with an instantaneous field-of-view
of ~2 sr.