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GCN Circular 28511

GRB 200925B NUTTelA-TAO / BSTI Early Measurements (Preliminary)
2020-09-27T05:14:22Z (3 years ago)
Bruce Grossan at LBNL/UCB SSL <>
B. Grossan (UCB, NU) , Z. Maksut (NU), A. Kim (NU), M. Krugov (FAI), G. F. Smoot (HKUST, UCB, NU), E. Linder (UCB, NU), report on behalf of the Energetic Cosmos Laboratory:

The Nazarbayev University Transient Telescope at Assy-Turgen Astrophysical Observatory (NUTTelA-TAO) pointed at GRB200925B on receipt of an automated GCN / BAT position alert. We report measurements made with the Burst Simultaneous Three-Channel Imager (BSTI; Grossan, Kumar & Smoot 2019, JHEA, 32,14) instrument  ***during commissioning phase*** and we note cautions with these measurements below.

Calibration with bright Pan-STARRS catalog I stars on our images, for our standard SDSS filters and 45 s co-added images yields, *without color corrections*, the following photometric values for the OT consistent with the position given in Evans et al. (GCN 28503): 

#	tc-t0(s)	g'(mag) 	   r'(mag)     i'(mag)
--	---------	-----------	  -----------  ------------
1	67.5   	UL18.27     UL18.07 UL17.32
2      136.5   	UL18.15      18.62      17.94** 
3      181.5   	UL18.21      17.99      17.47
4      226.5   	UL18.25      18.09      17.63
5      271.5   	UL18.27      18.17      17.48
6      316.5   	UL18.31      18.26      17.70
7      361.5   	UL18.14      18.60      17.83
8      406.5   	UL18.17      18.55      17.87*

UL = 5 sigma upper limit
** = very large certainty, close to limit ; poor by-eye confirmation and aperture centering
* = large uncertainty ; poor by-eye confirmation and aperture centering
Other uncertainties are estimated at ~ 0.1 mag
tc-t0 = trigger time minus image center time.

The measurements suggest that the early emission peaked ~180 s after trigger.

We caution the reader that the BSTI instrument is in commissioning phase, with known imperfections, and we have not extensively tested our results, e.g. against other simultaneous measurements, or near our detection limits. Please also note that the times are approximate. We anticipate additional analysis in 15-30 days posted at Some earlier images may have usable data. 

UCB = University of California, Berkeley, USA
NU = Nazarbayev University, Nur-Sultan, Kazakhstan
HKUST = Hong Kong University of Science and Technology
FAI = Fesenkov Astrophysical Institute, Kazakhstan 

The NUTTelA-TAO Team acknowledges the support of the staff of the Assy-Turgen Astrophysical Observatory, Almaty, Kazakhstan, and the Fesenkov Astrophysical Institute, Almaty, Kazkhstan.
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