GCN Circular 8993
Markku Nissinen (Varkaus, Finland) reports to the AAVSO High Energy Network the following optical observations of GRB 090313 (Chornock, Li, and Filippenko, GCN #8979; Mao et al., GCN #8980): Markku Nissinen reports the detection of the optical counterpart of GRB 090313 using the GRAS-04 telescope sited in Mayhill, NM, USA. A number of unfiltered observations with varying exposure times were made using the 0.25-meter telescope with an SBIG ST8XE CCD camera; observations began approximately 1 hour post burst. The afterglow was detected in all frames with astrometric positions matching those given by Chornock, Li, and Filippenko (GCN #8979) and Updike et al (GCN #8983) to within positional errors. The following unfiltered magnitudes were obtained from the observations using USNO-A2.0 U0975_07146255 (R magnitude = 15.9) as the comparison: obs midpoint(UT) exptime mag(CR) mag.err 2009-03-13 10:14:41 360 sec 16.5 +/- 0.3 (3 x 120 sec) 2009-03-13 10:27:59 300 sec 16.7 +/- 0.3 2009-03-13 10:39:53 600 sec 16.9 +/- 0.3 A FITS image of the 300-second observation is available at the following URL: ftp://ftp.aavso.org/grb/MarkkuNissinen_GRB090313_2454904.28608_.fits The AAVSO thanks the Curry Foundation for their continued support of the AAVSO International High Energy Network.