GCN Circular 7657

Arto Oksanen (Muurame, Finland) and Veli-Pekka Hentunen (Varkaus, Finland) 
report to the AAVSO High Energy Network the following optical observations 
of GRB 080430 (Guidorzi et al., GCN Circular #7647):

Arto Oksanen (Hankasalmi Obs., Hankasalmi, Finland) reports the detection 
of the optical counterpart of GRB 080430.  Unfiltered observations were 
made using a 0.4-meter RC telescope with an SBIG STL-1001E CCD.  The 
initial Swift XRT position was observed unfiltered with an initial set of 
10 60-second exposures having a mid-point time of 2008 April 30, 20:08:54 
UT; the afterglow was detected with a magnitude of 18.1 +/- 0.05 
calibrated relative to GSC 3450-0639.  Astrometry of the initial frames 
yields a position of RA 11:01:14.76 , Dec +51:41:08.9 (USNOA2.0 ref, +/- 
0.4 arcseconds), which is within the stated uncertainties of the UVOT 
position (GCNCirc #7647).

Images taken between April 30.839 and April 30.969 UT were reanalyzed and 
calibrated relative to two USNO-B1.0 stars of magnitude ~16.5. Photometry 
of combined frames yields a smoothly decaying light curve during the span 
of observations:

    obs midpoint 	  CR	error
2008 April 30.839	17.798	0.088
2008 April 30.849	18.329	0.120
2008 April 30.860	18.484	0.087
2008 April 30.875	18.751	0.076
2008 April 30.893	18.868	0.055
2008 April 30.911	18.956	0.052
2008 April 30.929	19.044	0.067
2008 April 30.949	19.012	0.064
2008 April 30.969	19.156	0.076

A detailed report of the initial observations is available at the following URL:
ftp://ftp.aavso.org/grb/A.Oksanen_GRB080430_2454587.38588_.txt

A FITS image of this observation is available at the following URL:
ftp://ftp.aavso.org/grb/A.Oksanen_GRB080430_2454587.38588_.fits


Markku Nissinen and Veli-Pekka Hentunen (Taurus Hill Observatory, Varkaus, 
Finland) also report the detection of the optical afterglow of GRB 080430. 
Observations were made using a Meade LX-200 0.3-meter telescope with an 
SBIG ST8-XME CCD; observations were made using both clear and R filters. 
A total of six 600-second exposures were obtained having an average 
midpoint time of 2008 April 30.943.  Photometry of the combined clear and 
Rc frames yields magnitudes of CR=19.2+/-0.3 and R=19.5+/-0.5 calibrated 
relative to the GSC2.3 star N7JI005540.  The observers noted the sky was 
not completely dark due to their high latitude and time of year.

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