GCN Circular 4977
M. Koppelman (Starhouse Observatory and University of Minnesota) reports on behalf of the AAVSO International High Energy Network on optical observations of GRB060418 (GCN #4966, Falcone et al.) and its reported optical afterglow (GCN #4968, Melandri et al.; GCN #4971, Nysewander et al.; GCN #4972, Cobb et al.): Koppelman reports the following Rc-band measurement: 03:46:20 UT Rc=16.47+/-0.14. Rc magnitudes are untransformed and differential with respect to a two-star ensemble with USNO B1.0 stars 0863-0300553 (R=14.86) and 0864-0294924 (R=14.22). Scatter in the check star was 0.05 mag. A detailed report of these observations follows at the end of this report. M. Nicholson (International Consortium of Robotic Astronomical Researchers) reports V-band observations of this afterglow approximately three hours after the burst. Analysis of these observations is continuing. The AAVSO thanks the Curry Foundation for their continued support of the AAVSO International High Energy Network. Rc-band observations by M. Koppelman, Starhouse Observatory: ----------------------- Name: Michael Koppelman email: michael at aps.umn.edu Observer: Michael Koppelman (KMP) Site: Starhouse Observatory Location: Cologne, MN LatitudeLongitude: 45N 93W Elevation: 800' Scope: Newtonian 0.212m ScopeFocalRatio: f/3.9 CCDVendor: SBIG ST-7XME CCDDetector: Kodak KAF-0402ME CCDSize: 765x510 CCDPixelScale: 2.26"/px CCDFOV: 30x20 Object: GRB060418A ObsDate: 2006-04-18 ObsMidPointTime: 2006-04-18 03:46:22 TimePerFrame: 60, 120 and 180s NumberOfFrames: 10 Filters: Rc Processing: bias, dark, flat Seeing: LimitingMag: Sky: Good afterglowmag: 16.47 afterglowerr: 0.14 compstars: B1.0 0863-0300553 and 0864-0294924 Report: I observed the afterglow at high air mass (~5) with an Rc filter. Plate solution yields a position of 15:45:42.54 -03:38:21 with an error of about 1". The afterglow is visible on 1 of 10 images but reliably detected above the sky background on 2 other images for a total of 3 positive detections. JD Rc Err 2453843.6530 16.44 0.39 2453843.6600 16.57 0.22 2453843.6621 16.37 0.22 Rc magnitudes are untransformed and differential with respect to a two-star ensemble with USNO B1.0 stars 0863-0300553 (R=14.86) and 0864-0294924 (R=14.22). Scatter in check star was 0.05m. Fits images and photometry available upon request to michael at aps.umn.edu.