TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  4971
SUBJECT: GRB 060418: PROMPT Detections
DATE:    06/04/18 06:05:55 GMT
FROM:    Melissa Nysewander at UNC,Chapel Hill  <mnysewan@physics.unc.edu>

M. Nysewander, K. Ivarsen, A. Foster, D. Reichart, J. Haislip, A. LaCluyze,
A. Trotter, J. A. Crain, J. Kirschbrown, and C. MacLeod report on behalf of
the UNC team of the FUN GRB Collaboration:

Skynet observed the localization of GRB 060418 (Falcone et al., GCN 4966)
with one of the 16-inch PROMPT telescopes at CTIO beginning 40 sec after
the burst (15 sec after notification).  We weakly detect the afterglow
(Falcone et al., GCN 4966) at z = 15.3 +/- 0.3 mag (calibrated to three
USNO-B1.0/NOMAD stars) in a 5-sec exposure taken at this time.

Observations were then interrupted until about 16 minutes after the burst
due to an unfortunately scheduled operating system update.

Skynet resumed observations with three of the PROMPT telescopes in Ugriz
(three simultaneously), with clear detections in 80-sec griz exposures.

At 16.6 minutes after the burst, we measure z = 14.44 +/- 0.02 mag,
implying a brightening of the afterglow at early times.  At 1.3 hours after
the burst, we measure z = 16.2 +/- 0.1 mag.  If fading as a power law
between these times, this implies a temporal index of about -1.1.

PROMPT is currently being built and commissioned.