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GCN Circular 20820

Subject
GRB 170306A: LCO Cerro Tololo observations
Date
2017-03-06T09:02:26Z (7 years ago)
From
Cristiano Guidorzi at Ferrara U,Italy <guidorzi@fe.infn.it>
C. Guidorzi (U. Ferrara), S. Kobayashi, I.A. Steele (LJMU), A. Gomboc 
(U. Nova Gorica), C.G. Mundell (U. Bath) on behalf of a large 
collaboration report:

We observed Swift GRB 170306A (Markwardt et al. GCN 20819) on March 6, 
07:26:06 UT (~20 minutes since the GRB trigger time) with the 1-m LCO 
unit in Cerro Tololo with SDSS r and i filters. Within the Swift XRT 
error circle we detect an uncatalogued source at the following position:

RA(J2000) = 17:32:16.76
Dec(J2000)= -44:44:53.7

with an error radius of 1". We find the following magnitude values as 
calibrated against nearby USNOB-1 objects (R2 and I values):

Mid Time      Exposure       Filter       Magnitude (AB)
(min)           (s)
-------------------------------------------------------
24            5x60           SDSS-I        18.5 +- 0.2
34            5x60           SDSS-R        19.0 +- 0.2
-------------------------------------------------------

At the moment we cannot make any statement on the temporal behaviour of 
the source. The expected Galactic dust extinction is A_r=1~mag, A_i=0.7 
mag (from Schlafly et al. 2011). Given the crowded field, we caution 
that the source might be unrelated to the GRB.
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