GCN Circular 26605
Subject
LIGO/Virgo S191216ap: Two candidate counterparts from UKIRT/WFCAM z-band observations
Date
2019-12-28T16:40:33Z (5 years ago)
From
Graham P Smith at U of Birmingham <gps@star.sr.bham.ac.uk>
G. P. Smith (Birmingham), M. Nicholl (Birmingham), K. Sharon (Michigan),
M. Bianconi (Birmingham), W. P. Varricatt (UKIRT), S. Benigni (UKIRT),
and E. J. Ridley (Birmingham) report on behalf of the Gravitationally
Lensed Gravitational Wave Hunters:
As part of our search for strongly-lensed gravitational waves and their
electromagnetic counterparts, we observed a contiguous area of 0.75
square degrees within the sky localization of the gravitational wave
trigger S191216ap (GCN #26454) with the WFCAM instrument on UKIRT
through the z-band. The observations were centered on the position of
the HAWC sub-threshold detection of gamma-ray flux reported by
Martinez-Castellanos (GCN #26472), and encompassed the full extent of
their 68% confidence region. The observations comprise two epochs:
Epoch Date(UT) Start(UT) End(UT) Airmass FWHM(arcsec)
1 2019-12-20 04:45:21 05:45:57 1.3-1.7 1.2-1.6
2 2019-12-21 04:31:26 05:43:34 1.3-1.8 1.6-1.8
We estimate that Epoch 1 reaches a 5 sigma point source sensitivity of
AB~21.5. Epoch 2 is less sensitive than Epoch 1, with noticeable
variations in Epoch 2 between the four observations required to achieve
contiguous coverage with WFCAM.
A preliminary comparison of Epoch 1 with templates derived from
Pan-STARRS1 data (nominal sensitivity of AB=22.3) identified two
candidate transient sources. Neither source is known to the Transient
Name Server, and Minor Planet Center. The celestial coordinates and
estimated z-band apparent AB magnitudes of these two candidates are:
Name RA(J2000) Dec(J2000) AB(Epoch1) AB(Epoch2)
GLGWc19a 21:32:45.50 +05:19:58.0 20.8+/-0.1 ~22
GLGWc19b 21:35:20.11 +04:55:19.8 20.6+/-0.1 >20(tentative)
Neither source is associated with an obvious candidate gravitational
lens (i.e. massive galaxy, group or cluster) to the depth of the PS1
data. However, GLGWc19a is 7 arcsec West, 1 arcsec North of the center
of an edge-on disk galaxy (possible host?) that is located at
21:32:45.97 +5:19:57.0.
These sources are observable at Airmass<2 for ~30 minutes following the
end of evening twilight in the Northern Hemisphere in the next few
nights, before becoming unobservable through the winter months. We
therefore encourage urgent follow-up observations of GLGWc19a, GLGWc19b
and the candidate host galaxy adjacent to GLGWc19a.
We thank the Director of UKIRT, Klaus Hodapp, for quickly approving our
urgent DDT proposal. We are also grateful to Mike Irwin for kindly
expediting the processing of our data at Cambridge Astronomy Survey Unit
(CASU).
This circular is citable.