[vsnet-grb-info 6836] GRB081028: UVOT detection of a brightening afterglow

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  8431
SUBJECT: GRB081028: UVOT detection of a brightening afterglow
DATE:    08/10/28 15:40:08 GMT
FROM:    Patricia Schady at MSSL/Swift  <ps at mssl.ucl.ac.uk>

P. Schady (MSSL-UCL) and C. Guidorzi (INAF-OAB) report on behalf of  
the Swift/UVOT team:

Further to the UVOT observations of GRB 081028 reported in GCN Circ.  
8430 (Schady et al.), we report an afterglow detection at the position  
of the optical counterpart (GCN Circ. 8424, GCN Circ. 8425) in later  
UVOT observations, from 10,000s after the BAT trigger. This is  
suggestive of a re-brightening of the afterglow consistent with the  
time of the brightening observed in the XRT light curve (Guidorzi et  
al., GCN Circ. 8429). The afterglow is detected in the v, b and u-band  
filters. The detection of the afterglow in the u-filter suggests a  
photometric upper limit on the redshift of z < ~2.3.

The magnitudes of the afterglow and 3-sigma upper limits are reported  
below:

Filter Tstart(s)   Tstop(s)    Exp(s)    Magnitude/3-sig UL
v          4050         5684        393.2        > 20.13
v          10740       28995     1770.3      20.23 +/- 0.19

b          4870         6504        393.3        > 20.79
b          17436       35567     1433.5     20.19 +/- 0.14

u          4665         6299        393.2       > 20.53
u          16524       34778     2539.8     21.21+/- 0.26

uvw1   4460         6094        393.2       > 20.61
uvw1   15618      33865      2656.7     > 21.89

uvm2   4255        5889        393.2        > 20.51
uvm2   21399      29784     2428.5      > 21.66

uvw2   5281         5480       196.6        >  20.23
uvw2   29001      28082     1771.2      >  20.61


The above magnitudes are not corrected for the Galactic extinction  
corresponding to a reddening of E(B-V) = 0.03 mag (Schlegel et al.,  
1998, ApJS, 500, 525). The photometry is on the UVOT photometric   
system described in Poole et al. (2008, MNRAS, 383,627).