GCN Circular 14287

GRB 130306A: Swift Detection of a Possible Afterglow

M. H. Siegel (PSU), David N. Burrows (PSU) and Dirk Grupe (PSU)
report on behalf of the Swift team:

On 8 March 2013 the Swift spacecraft performed a delayed observation of the
BAT-detected burst GRB 130306A (Siegel et al., GCN 14266
Not found
 
 
), which was also
detected by Fermi GBM (Pelassa, GCN 14270
Not found
 
 
) and Konus/Wind (Golenetskii et al.,
GCN 14275
Not found
 
 
).

We have analyzed 5.1 ks of XRT data, from 146 to 163 ks after the Swift/BAT
trigger.   The data are entirely in photon counting (PC) mode. 
An X-ray source is detected within the Swift/BAT error circle. The XRT 
position is RA, Dec = 279.46147, -11.68123 which is equivalent to:

RA (J2000) = 18 37 50.75
Dec(J2000) = -11 40 52.4

with an uncertainty of 4.0 arcsec (radius, 90% confidence).  We do not detect
any fading over the time span of the Swift observations.

The Swift/UVOT began settled observations of the field of GRB 130306A 146 
ks after the Swift/BAT trigger.  No optical afterglow consistent with the XRT position
is detected in the initial UVOT exposures. Preliminary 3-sigma upper limit using the
UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the
initial exposures are:

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

uvw1         145609      162770         4707         >22.2

The magnitudes in the table are not corrected for the Galactic 
extinction due to the reddening of E(B-V) = 0.15 in the direction of the 
burst (Schlegel et al. 1998).

Further observations are planned to determine if the source is fading.