TITLE: GCN CIRCULAR NUMBER: 7657 SUBJECT: GRB 080430 optical observations DATE: 08/05/01 16:35:47 GMT FROM: AAVSO GRB Network at AAVSO 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.