TITLE: GCN CIRCULAR NUMBER: 10073 SUBJECT: GRB091024: VRcIc Afterglow Observations DATE: 09/10/24 20:09:04 GMT FROM: Arne A. Henden at AAVSO A. Henden (AAVSO), J. Gross (SRO), B. Denny (DC-3), D. Terrell (SwRI), and W. Cooney (SRO) report: We obtained photometry of the GRB091024 afterglow reported by Mundell et al. (GCN 10063) using the Sonoita Research Observatory (SRO) 35cm telescope in southern Arizona, utilizing an automatic VOevent trigger. The Rc-band exposures began about 9 minutes after the burst and continued for approximately one hour. Ten Rc-band, nine V-band, and one Ic-band exposures were acquired. Photometry, assuming that USNO-B1.0 1468-0448363 (RA: 22:36:44.11 , Dec: +56:52:42.6) has the following magnitudes: V=13.46, R=12.93, I=12.71 UT(mid) delT exp mag err filter 09.1122 642 180 17.177 0.030 Rc 09.1667 839 180 17.510 0.037 Rc 09.2192 1028 180 17.827 0.049 Rc 09.2722 1218 180 17.993 0.044 Rc 09.3247 1407 180 18.136 0.056 Rc 09.4123 1723 300 18.008 0.046 Rc 09.5000 2038 300 17.764 0.045 Rc 09.5859 2348 300 17.737 0.033 Rc 09.6717 2657 300 17.665 0.037 Rc 09.7575 2965 300 17.776 0.045 Rc 09.8609 3338 300 19.029 0.111 V 09.9486 3653 300 19.267 0.120 V 10.0348 3964 300 19.290 0.132 V 10.1206 4273 300 19.320 0.126 V 10.2064 4581 300 19.237 0.091 V 10.2923 4891 300 19.345 0.151 V 10.4642 5510 300 19.163 0.107 V 10.5500 5818 300 19.293 0.123 V 10.6359 6128 300 19.350 0.163 V 10.8439 6877 180 17.550 0.074 Ic Where delT is the time in seconds from the burst (Marshall et al., GCN 10062), and the exposure is in seconds. Astrometry from the Rc frames, using UCAC3, yields a precise position of 22:36:59.68 +56:53:23.3 J2000 (+/- 100mas). A full BVRcIc calibration is in the Sonoita queue and will be released when photometric conditions permit. The AAVSO thanks the Curry Foundation for its support of the AAVSO International High Energy Network.