TITLE:   GCN CIRCULAR
NUMBER:  14697
SUBJECT: GRB 130521A: Skynet/PROMPT observations
DATE:    13/05/23 02:23:02 GMT
FROM:    Adam S. Trotter at UNC-Chapel Hill/PROMPT/Skynet  <atrotter@physics.unc.edu>

D. James, C. Foster, P. Taylor, M. Carroll, A. Trotter, D. Reichart, A. 
LaCluyze, J. Haislip, T. Berger, H. T. Cromartie, R. Egger, A. Foster, 
N. Frank, K. Ivarsen, M. Maples, J. Moore, M. Nysewander, E. Speckhard, 
and J. A. Crain report

Skynet observed the Swift/BAT localization of GRB 130521A (Pagani et 
al., GCN 14691, Swift trigger #556344) with four 16" telescopes of the 
PROMPT array at CTIO, Chile.  Starting at 2013-05-21, 22:49:16 UT and 
continuing until 23:01:04 UT (t=49.2s-11.8m post-trigger), it took 66 
exposures in the BVRI bands. We did not detect a fading afterglow within 
the 3 arcmin radius of the Swift/BAT error circle, which was centered on 
RA 05h50m14.2s, Dec +14d27m08.6s (J2000.0).

A plot of the 3-sigma limiting magnitudes in each exposure, calibrated 
to six USNO-B1/NOMAD stars in the field, is here:
http://skynet.unc.edu/grb/grb130521a.png

We stacked all the images in each band and obtained 3-sigma limiting 
magnitudes on any afterglow of:
Filter       B       V       R       I
Mag       >18.29  >18.53  >18.13  >17.07

Magnitudes are Vega magnitudes, and have not been corrected for the 
expected line-of-sight Milky Way dust extinction E(B-V)=0.38 (Schlegel 
et al. 1998).

No further Skynet observations are scheduled.