[vsnet-grb-info 15933] GRB 141221A: Continued Skynet PROMPT-CTIO observations

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  17221
SUBJECT: GRB 141221A: Continued Skynet PROMPT-CTIO observations
DATE:    14/12/22 20:18:17 GMT
FROM:    Adam S. Trotter at UNC-Chapel Hill/PROMPT/Skynet  <atrotter at physics.unc.edu>

A. Trotter, J. Haislip, D. Reichart, A. Aji, R. Beauchemin, T. Berger, 
A. Dow, A. Foster, N. Frank, M. Hinckle, K. Ivarsen, A. LaCluyze, M. 
Maples, J. Moore, M. Nysewander, C. Salemi, L. Zbinden, and J. A. Crain 
report:

Skynet continued to observe the Swift UVOT localization of GRB 141221A 
(Sonbas et al., GCN 17206, Swift trigger=622006) with two 16" telescopes 
of the PROMPT array at Cerro Tololo, Chile. Starting at 2014-12-22 07:08 
UT and continuing until 08:34 UT (t=23.0h-24.5h post-trigger), Skynet 
took a total of 64 exposures of 160s each in the V and I bands. We 
stacked subsets of these images to maximize the signal-to-noise ratio. 
We no longer detect the optical afterglow that we described in Trotter 
et al. (GCN 17210).

Our limiting magnitudes are:

==================================
tmid  expos  fil  limit
==================================
23.8h 32x160s V   >21.2
23.8h 31x160s I   >20.7

A preliminary light curve is at:

http://www.skynet.unc.edu/grb/grb141221a_2.png

Magnitudes are in the Vega System, calibrated to 3 APASS stars in the 
field.  Magnitudes have not been corrected for line-of-sight Milky Way 
dust extinction, with expected E(B-V)=0.024 (Schlafly & Finkbeiner 2011).

No further Skynet observations are scheduled.