TITLE:   GCN CIRCULAR
NUMBER:  25492
SUBJECT: LIGO/Virgo S190814bv: Optical non-detection of radio source AT2019osy from CFHT 
DATE:    19/08/27 16:41:04 GMT
FROM:    John J. Ruan at McGill U  <jjr2125@gmail.com>

J. Ruan (McGill U.), N. Vieira (McGill U.),
D. Haggard (McGill U.), M. R. Drout (U. of Toronto),
N. Asfari (U. of Toronto), R. Carlberg (U. of Toronto),
R. Doyon (U. de Montreal), R. Fernandez (U. of Alberta),
B. Gaensler (U. of Toronto), D. Lafreniere (U. de Montreal),
C. Matzner (U. of Toronto), D-S. Moon (U. of Toronto),
C. Ni (U. of Toronto), M. Nynka (MIT),
A. L. Piro (Carnegie Obs.), S. Safi-Harb (U. of Manitoba),
K. Spekkens (RMC/Queen's U.)

We report upper-limits from our CFHT non-detections of the
optical counterpart to AT2019osy, including deep g-band
imaging within a few hours of the DECam detection.

AT2019osy was originally reported as a rising radio source in ASKAP
observations (GCN 25487), lying within the 95% localization volume
of LIGO/Virgo S190814bv (GCN 25333). An optical counterpart was
subsequently reported in DECam observations at MJD 5816.26
(GCN 25488), with a preliminary magnitude of i=22.3.

Previously, we used the MegaPrime/MegaCam instrument on CFHT to
tile the localization region of LIGO/Virgo S190814bv. Our imaging
covered AT2019osy multiple times, including deep g-band observations
within hours of the DECam observations that discovered the optical
counterpart with i=22.3 mag on MJD 58716. We do not detect
AT2019osy in our images, and report the following upper limits:

MJD, days post-merger, band, mag
58711.5,   1.7 days,   g,   >21.85
58713.5,   3.6 days,   i,   >22.50
58716.5,   6.6 days,   g,   >23.50

We thank the CFHT queued service observing team and the telescope
staff for their help in obtaining these observations.