GCN Circular 26227

Hank Corbett (University of North Carolina), Kendall Ackley (Monash), Nicholas Law,
Ramses Gonzalez Chavez, Alan Vasquez, Jeffrey Ratzloff (UNC), Stephen S. Eikenberry (University of Florida),
Ward Howard, Amy Glazier, Nathan Galliher, Dan Reichart,
Josh Haislip, and Vladimir Kouprianov (UNC), Robert Quimby (San Diego State University)

The contact person for this circular is Hank Corbett (htc@unc.edu).

Evryscope-South, located at Cerro Tololo Inter-American Observatory, (Ratzloff et al. 2019, Law et al. 2015)
began observing the error region of LIGO/Virgo S191110af at 2019-11-11 01:00:05 UT during regular
science operations.  Evryscope-South has an instantaneous field of view of 8520 sq. degrees and observes
at a continuous 2-minute cadence in Sloan g'.

Evryscope-North, located at Mount Laguna Observatory, California, began observing the error region
of LIGO/Virgo S191110af at 2019-11-11 01:35:30 UT during regular science operations. Evryscope-North
has an instantaneous field of view of 7409 sq. degrees and observes at a continuous 2-minute cadence in Sloan g'.

Under current full-moon conditions, single-exposure limiting magnitudes ranged from 12.5 to 14.5 as
a function of moon elongation and airmass, averaging 13.7, calibrated to the ATLAS All-Sky Stellar
Reference Catalog (Tonry 2018).

We performed an automated search for optical transients over all Evryscope-South images within
5 hours of the alert, selecting candidates that appeared in multiple frames and were not associated
with previously-detected variable sources. During this interval, Evryscope-South observed 93% of the
LIGO/Virgo skymap and Evryscope-North observed 2% of the skymap. We found no candidates
within the visible 90% probability containment region for S191110af. Evryscope-North data analysis is ongoing.