We have observed the field of GRB050502b (09:25:40 UT) covering the SWIFT XRT error circle (Pagani et al., GCN 3333) by the Ashra-AFT (Automated Follow-up for Transients) telescope at the Haleakala observatory in Hawaii (latitude = 20d 42' 37" N, longitude = 156d 15' 31" W, altitude = 3020m). The telescope (12" Meade LX200GPS with a KAI-2020M CCD) is served as a follow-up detector to quickly respond to triggers from Ashra optical transient survey monitor as well as from GRB satellites.
The telescope automatically slewed to the GRB and took the first image of 1.4sec-exposure at 09:26:36 UT (56 seconds after the burst and 32 seconds after the BAT alert socket). We also took following 363 images of 4sec-exposure every 9 to 10 seconds (09:26:36 UT - 10:25:47 UT). These images are unfiltered to maximize the detection sensitivity, of which peak is between B and V.
No new source was found within the SWIFT XRT position. From the earliest 4 images and the co-added images (3 x 4sec, 25 x 4sec), we preliminarily obtained 4-sigma limiting magnitudes of B1 and R1 in the USNO-B1.0 catalog as follows.
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start end exposure limit mag.
after GRB (s) (s) B1 R1
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56.0 57.4 1.4 16.2 14.6
66.0 70.0 4.0 16.9 15.5
76.0 80.0 4.0 16.2 14.6
85.0 89.0 4.0 16.2 14.6
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66.0 89.0 12.0 17.2 16.2
66.0 294.0 100.0 18.5 17.0
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URL: http://www.icrr.u-tokyo.ac.jp/~ashra/GRB050502b/
#N USNOB1.0-ID RA(J2000) DEC(J2000) B1 R1 B2 R2 I2 USNOA2.0-ID B R 1 1403-01629-1 09:30:33.8753 +16:57:07.960 12.850 12.380 12.690 12.360 12.220 1050-6065293 12.600 11.900 2 1069-0187092 09:30:03.2240 +16:59:55.800 13.880 12.190 12.740 11.130 10.820 1050-6063192 13.000 11.600 3 1069-0187072 09:29:59.7747 +16:54:59.280 14.800 13.730 14.190 13.690 13.140 1050-6062958 13.900 13.200 4 1069-0187164 09:30:24.4567 +16:55:10.770 15.170 14.150 14.740 14.320 13.900 1050-6064659 14.100 13.600 5 1070-0194705 09:30:07.4860 +17:01:57.390 15.250 14.090 14.690 14.240 13.870 1050-6063459 14.400 13.700 6 1069-0187105 09:30:07.1007 +16:55:53.610 15.410 14.530 15.030 14.620 14.250 1050-6063429 14.400 14.100 7 1069-0187163 09:30:24.3820 +16:55:42.510 15.540 14.810 15.210 14.900 14.480 1050-6064655 14.500 14.500 8 1070-0194741 09:30:17.8040 +17:02:25.900 15.720 14.210 15.170 14.320 13.840 1050-6064190 14.900 14.000 9 1070-0194671 09:29:56.1407 +17:01:16.540 16.240 14.560 15.470 14.750 14.340 1050-6062701 15.400 14.400 10 1069-0187162 09:30:23.8900 +16:56:02.430 16.670 16.160 16.550 15.910 16.010 1050-6064625 15.800 15.800 11 1069-0187102 09:30:06.6160 +16:58:58.930 16.890 15.520 16.260 15.430 14.890 1050-6063395 15.900 15.300 12 1070-0194690 09:30:01.0573 +17:03:11.470 17.190 16.180 16.770 16.000 15.830 1050-6063052 16.300 16.000 13 1068-0182672 09:30:14.6300 +16:53:36.220 17.220 15.780 16.690 15.780 15.290 1050-6063953 16.200 15.600 14 1068-0182663 09:30:12.0273 +16:53:38.330 17.300 14.850 16.500 14.900 13.820 1050-6063780 16.300 14.500 15 1069-0187087 09:30:02.4107 +16:56:05.700 17.470 15.820 16.740 15.640 15.200 1050-6063137 16.600 15.500 16 1070-0194759 09:30:23.7873 +17:01:15.820 17.500 16.300 16.850 16.210 15.800 1050-6064616 16.700 16.100 17 1070-0194755 09:30:22.8407 +17:01:17.840 17.520 16.300 17.060 16.320 15.970 1050-6064538 16.600 16.100 18 1069-0187136 09:30:16.6333 +16:59:16.320 17.530 16.170 16.910 16.420 15.890 1050-6064088 16.600 15.900 19 1068-0182626 09:30:04.2467 +16:52:41.820 17.630 16.540 17.050 16.370 15.900 1050-6063253 16.700 16.300 20 1069-0187134 09:30:16.3980 +16:57:55.150 17.850 15.750 16.930 15.520 14.970 1050-6064074 17.000 15.400 21 1069-0187120 09:30:12.1100 +16:57:31.980 17.940 16.910 17.330 16.630 16.720 1050-6063790 17.000 16.700 22 1069-0187181 09:30:28.8420 +16:58:25.050 18.210 16.430 17.540 16.300 15.710 1050-6064959 17.300 16.100 23 1070-0194724 09:30:12.6813 +17:00:04.960 18.340 16.120 17.440 16.230 15.670 1050-6063826 17.500 15.900 24 1068-0182651 09:30:09.7940 +16:52:31.440 18.450 17.000 17.620 17.180 16.670 1050-6063647 17.500 16.900
