GCN Circular 6154

Christina C. Thoene (Dark/NBI), D. Alexander Kann (TLS Tautenburg), Thomas                                                    
Augusteijn (NOT) and Celine Reyle-Laffont (Observatoire de Besancon) 
report:

We observed the OT candidate (Thoene et al., GCN 6142
Not found
 
 
) of GRB 070224 
(Racusin et al., GCN 6137
Not found
 
 
) again on Feb. 27 (2.27 days after the burst) 
with NOT and StanCam in R.

The proposed candidate (Thoene et al., GCN 6142
Not found
 
 
, see also Chen et al., GCN
6145
Not found
 
 
, Mirabal et al., GCN 6146
Not found
 
 
, Rol et al., GCN 6147
Not found
 
 
 and Chen et al., GCN 
6148
Not found
 
 
) is clearly fading between our three epochs.                               

We get the following magnitudes:

t after burst�� exptime�� R mag:
0.20 d����������� 900s��������22.1 +- 0.2 
0.39 d����������� 1800s������ 22.5 +- 0.2
2.27 d����������� 2400s������ 24.1 +- 0.3

based on two nearby USNO-B1.0 stars.

We therefore conclude that this object is the afterglow of GRB 070224.
It thus may have had an early plateau phase (Rol et al., GCN 6147
Not found
 
 
, Chen et 
al., GCN 6148
Not found
 
 
).

Improved astrometry gives a refined position of the afterglow at (J2000):

RA = 11:56:06.65  
Dec = -13:19:48.8  
 
with an error of 0.5 arcsec. 

This is 1.1 arcsec from the center of the revised XRT error circle 
(Racusin et al., GCN Report 36.1) and 0.8 arcsec from the center of Nat 
Butler's error circle (v2.5) 
(http://astro.berkeley.edu/~nat/swift/xrt_pos.html).