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GCN Circular 21245

Subject
LIGO/Virgo G288732: UKIRT near-IR imaging of the Fermi/LAT candidate
Date
2017-06-11T01:47:00Z (7 years ago)
From
Wen-fai Fong at U of Arizona <wenfai@gmail.com>
W. Fong, 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 Wide Field Camera (WFCAM) mounted on the 3.8-m United
Kingdom Infrared Telescope (UKIRT) on Mauna Kea beginning on 2017 Jun 9.238
UT (1.15 days post-trigger; LSC/Virgo et al. GCN 21221). We obtained a
total of 360-sec of J-band imaging in 1.4" seeing at a mean airmass of 1.8.
The observations cover the entire Fermi/LAT localization region (90%
confidence; Omodei et al., GCN 21227), as well as the positions of all
Swift/XRT sources reported in Evans et al. (GCN 21233).

To assess variability, we obtained a second set of observations beginning
on 2017 Jun 10.240 UT (2.16 days post-trigger and 24.0 hr after the initial
UKIRT observations). These observations cover only 75% of the Fermi/LAT
localization area, as well as the positions of XRT Sources 2-7.

We perform photometry of all known near-IR sources in or around the
positions of the XRT sources, and find no evidence for variability relative
to archival 2MASS values. Digital image subtraction of the two UKIRT epochs
using the ISIS software package reveals no residuals, indicating no
variability from 1.15 to 2.16 days post-trigger for 75% of the LAT
localization region, to a 3-sigma limit of J>18.9 AB mag. We note that this
preliminary analysis is based on reductions produced by the quick-look
pipeline ORAC-DR, and a final reduction of the images are expected to be at
least ~1.5 mag deeper.

We thank Sam Benigni and Watson Varricatt for their assistance in planning
and executing these observations."
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