A. LaCluyze, D. Reichart, J. Haislip, K. Ivarsen, R. Egger, A. Foster, J.
Moore, A. Oza, M. Schubel, J. Styblova, A. Trotter, J. A. Crain, and M.
Skynet observed the Swift/BAT localization of GRB 091018 (Stamatikos et
al., GCN 10034) with four of the 16" PROMPT telescopes at CTIO beginning
3.0 hours after the the trigger in BVRI.
We detect the afterglow (Stamatikos et al., GCN 10034) in all filters.
Between 3.0 and 12.3 hours after the trigger, the afterglow faded with
periods of rebrightening (1) beginning around 5 hours and peaking around 6
hours, and (2) beginning around 8 hours and peaking around 9 hours.
Overall, if fitted with a power law, the afterglow faded with a power-law
index of about -0.95 in BVR but only about -0.65 in I. I - R brightened by
about 0.45 mag over the course of 12 hours.
At 12.3 hours after the trigger, the afterglow's magnitude was R = 19.82
+0.14 -0.12 (statistical) +/- 0.56 (systematic; calibrated to 115 USNO B1
Skynet's most recent BVRI light curve, calibrated to USNO B1 and NOMAD
stars, can be found here: