[vsnet-grb-info 3140] GRB060418: Optical Observations

[GCN Circulars]

TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  4977
SUBJECT: GRB060418: Optical Observations
DATE:    06/04/18 19:48:15 GMT
FROM:    AAVSO GRB Network at AAVSO  <aavso at aavso.org>

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.