GCN Circular 13114

N. P. M. Kuin (MSSL-UCL), S. Holland (STScI), and M. H. Siegel (PSU)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 120326A
67 s after the BAT trigger (Siegel et al., GCN Circ. 13105
Not found
 
 
).
A source consistent with the XRT position (Goad et al., GCN Circ. 13110
Not found
 
 

is detected in the initial UVOT exposures at position: RA (J2000)
= 18:15:37.13, Dec (J2000) = +69:15:35.36 or, in decimal degrees:
273.90471, 69.259822 with an uncertainty of 0.5" (90 % confidence).

The transient was initially increasing in brightness, and after a small
decay rebrightened around 10ks after the trigger. There is also some
indication of colour dependence of the time of rebrightening.

The detection in the UVOT uvw2 filter gives an upper limit for the
redshift of about z < 1.6 for this burst.

Preliminary detections and 3-sigma upper limits using the UVOT
photometric system
(Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the early exposures are:

Filter         T_start(s)   T_stop(s)      Exp(s)           Mag

white_FC            67          217          147        >20.0
white             3903         4103          197         20.16 +/- 0.12
v                 4314         5949          393        >19.3
b                 3697         5334          393         20.23 +/- 0.16
u                 4929         5128          197         19.66 +/- 0.20
m2                4518        16222         1228        >21.2
w2                4109         5744          393        >21.0
w1                9527        10427          886         20.21 +/- 0.18
v                21959        22259          295         18.67 +/- 0.12
w2               21052        21952          886         21.26 +/- 0.32

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.05 in the direction of the burst
(Schlegel et al. 1998).