TITLE:   GCN CIRCULAR
NUMBER:  21244
SUBJECT: LIGO/Virgo G288732: LBT optical imaging of the Fermi/LAT candidate
DATE:    17/06/11 01:33:37 GMT
FROM:    Wen-fai Fong at U of Arizona  <wenfai@gmail.com>

W. Fong, B. Rothberg, J. Hill, P. Milne, N. Smith and D. Zaritsky
(University of Arizona) report on behalf of the AZTEC (Arizona Transient
Exploration and Characterization) team:

"We observed the field of the Fermi/LAT candidate (Omodei et al., GCN
21227) with the Large Binocular Camera (LBC) mounted on the 2x8.4-meter
Large Binocular Telescope (LBT) on Mount Graham, Arizona beginning on 2017
Jun 10.156 UT (2.07 days post-trigger; LSC/Virgo et al. GCN 21221). We
obtained 26x30-sec of i-band imaging in 1.7" seeing at a mean airmass of
2.2. The observations cover 88% of the Fermi/LAT localization region (90%
confidence; Omodei et al., GCN 21227), as well as the positions of
Swift/XRT Sources 1-4 (Evans et al.; GCN 21233).

Inspection of the LBT observations relative to Pan-STARRS1 archival imaging
reveals no new sources in or around the positions of XRT Sources 1-4.
Moreover, photometry of the known optical sources are consistent with the
archival PS1 and SDSS values within the 1-sigma uncertainties,
corroborating the conclusions from shallower imaging with NOWT (Xu et al.,
GCN 21236) and Swift/UVOT (Emery et al., GCN 21235). Calibrated to SDSS
stars in the field, we estimate a 3-sigma limiting magnitude of i_AB>22.4
mag for the observations.

We thank LBT Director Christian Veillet for awarding this observing time."