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GCN Circular 30231

GRB 210610B: iTelescope optical afterglow observations
2021-06-13T18:36:43Z (3 years ago)
Arto Oksanen at Nyrola Obs., Finland <>
Markku Nissinen (Taurus Hill Observatory, Varkaus, Finland) and Arto Oksanen 
(Hankasalmi Observatory, Hankasalmi, Finland) report:

We have detected GRB 210610B optical afterglow (Page et al., GCN30170) using 
iTelescope T18 (0.32-m f/8.0 + CCD in AstroCamp at Nerpio, Spain), iTelescope T21 
(0.43-m f/6.8 + f/4.5 focal reducer + CCD in New Mexico Skies at Mayhill, 
New Mexico, USA) and iTelescope T11 (0.50-m f/6.8 + f/4.5 focal reducer + CCD 
in New Mexico Skies at Mayhill, New Mexico, USA). 

We took total of 24 exposures with clear (CR), V and R filters. 

The afterglow was clearly detected with each filter at the position
RA 16:15:40.43 DEC +14:23:57.4.  

The following magnitudes were measured from comparison of a nearby star
(V = 13.97, r'=13.70) from the APASS DR9 catalogue (Henden+, 2016):

JD            UTC            Mag    Err   Filter AirMass Telescope Exposure(s)
2459376.36806 June 10 20:50  16.79  0.05  CR     1.28    T18       7x60
2459376.37868 June 10 21:05  17.15  0.10  V      1.24    T18       10x60
2459376.64285 June 11 03:25  17.76  0.02  CR     1.29    T21       2x300
2459376.65108 June 11 03:37  17.95  0.12  R      1.26    T11       5x300

We used r' reference magnitude for the clear filter and the R filter measurements.
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