[vsnet-grb-info 2111] GRB 050908: Optical observations

[GCN Circulars]

TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  3950
SUBJECT: GRB 050908: Optical observations
DATE:    05/09/08 14:59:10 GMT
FROM:    Arto Oksanen at Nyrola Obs., Finland  <oksanen at nyrola.jklsirius.fi>

D. T. Durig, N. P. McLarty and J. R. Manning (Cordell-Lorenz 
Observatory) report on behalf of the AAVSO International High Energy 
Network on optical observations of GRB050908 (GCN #3942; Goad et al.):

The optical afterglow reported by K. Torii (GCN #3943) was detected and 
its fading behaviour was confirmed with observations starting 14 minutes 
after the Swift trigger. Full details and URL to the FITS image are below.

The AAVSO thanks the Curry Foundation for support of the AAVSO 
International High Energy Network.

Report filed on Thu Sep  8 06:22:58 2005:

 Name: Dr. Douglas T. Durig
 email: ddurig at sewanee.edu
 Observer: D. T. Durig, N. P. McLarty, J. R. Manning
 Site: Cordell-Lorenz Observatory
 Location: Sewanee, Tenn., USA
 LatitudeLongitude: 35 12 N 85 55 W
 Elevation: 600 m
 Scope: SCT 0.30 m
 ScopeFocalRatio: 1770 mm f/5.9
 CCDVendor: SBIG ST-8E
 CCDDetector: KAF 1600
 CCDSize: 1530x1020, binned 3x3
 CCDPixelScale: 3.15 arc sec
 CCDFOV: 26.7 x 17.8 arc min/13.35x8.9 shown
 Object: GRB050908
 ObsDate: 2005 09 08
 ObsMidPointTime: 07:59:09
 TimePerFrame: 300 sec
 NumberOfFrames: 48
 Filters: CR
 Processing: dark, flat, register, add, 1/2 frame crop
 Seeing: ~5 arc sec
 LimitingMag: ~21.5-22 ???
 Sky: mostly clear, occasional high clouds, no wind
 afterglowmag: 19th fading to 21st
 afterglowerr: 0.3 mag
 compstars: 310 USNO B1.0 stars in field

 Report: I had to use my backup CCD because my primary is in for repair. 
I started imaging at 05:56:39 ( 2453621.7477 JD ) and did 30 x 300 sec 
exposures followed by an additional 18. I was analysing the first 10 and 
had identified the potential candidate on my own. I was checking the 
fading behaviour when GCN 3943 from Torii announced the same candidate. 

I then used my first 20 frames added in sets of 5 to confirm clear 
fading 
behaviour:

8.25483 01 21 50.72 -12 57 17.4 19.3 R 
8.27272 01 21 50.73 -12 57 17.0 19.8 R 
8.29063 01 21 50.69 -12 57 17.1 20.4 R  
8.30853 01 21 50.79 -12 57 17.0 21.0 R 

I then used sets of 10 and 20 to get later data points for the full set 
of images.

Full data set:

08.25483 01 21 50.72 -12 57 17.4 19.3 R      850
08.26378 01 21 50.72 -12 57 17.2 19.6 R      850
08.27272 01 21 50.73 -12 57 17.0 19.8 R      850
08.28168 01 21 50.71 -12 57 17.2 19.9 R      850
08.29063 01 21 50.69 -12 57 17.1 20.4 R      850
08.29958 01 21 50.67 -12 57 17.8 20.7 R      850
08.33539 01 21 50.73 -12 57 15.8 20.2 R      850
08.35454 01 21 50.69 -12 57 16.9 21.0 R      850
08.37369 01 21 50.64 -12 57 18.1 21.4 R      850

A FITS image has been uploaded to: 
ftp://ftp.aavso.org/grb/Dr.DouglasT.Durig_GRB050908_2453621.93262_.fits