GCN Circular 3421

M. Sasaki, N. Manago, K. Noda, Y. Asaoka report on behalf of the Ashra collaboration:

We have observed the field of GRB050502b (09:25:40 UT) covering the SWIFT XRT error circle 
(Pagani et al., GCN 3333
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 ) 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. 

 -----------------------------------------------------
   start    end      exposure     limit mag.
   after GRB (s)          (s)     B1          R1
 -----------------------------------------------------
    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
 -----------------------------------------------------
    66.0    89.0    12.0          17.2        16.2
    66.0   294.0   100.0          18.5        17.0
 -----------------------------------------------------
 
URL: http://www.icrr.u-tokyo.ac.jp/~ashra/GRB050502b/

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