TITLE:   GCN CIRCULAR
NUMBER:  8359
SUBJECT: GRB081011: UVOT detection of an optical afterglow
DATE:    08/10/11 17:57:02 GMT
FROM:    Patricia Schady at MSSL/Swift  <ps@mssl.ucl.ac.uk>

P. Schady (MSSL-UCL) and D.Grupe (PSU) report on behalf of the Swift/UVOT 
team:

The Swift/UVOT observed the field of GRB 081011 (Grupe et al., GCN Circ. 
8355) with settled exposures starting 99s after the trigger. A new fading 
source is detected in the white and u-band finding chart (fc) exposures 
and marginally in a co-added b-band exposure at
RA(J2000) = 14:41:22.627 (220.34428)
Dec(J2000) = +33:32:37.12 (+33.54364)
consistent with the XRT position (Kennea et al., GCN Circ. 8358). These 
detections imply an upper limit on the redshift of z < ~3.8. The source is 
decaying with an approximate optical decay rate of alpha~1.1 (where the 
afterglow flux is proportional to t^-alpha).

The detections and 3 sigma upper limits in the UVOT photometric system 
(Poole et al. 2008, MNRAS, 383, 627) are:

Filter������������T_start T_stop�� Exp��    Mag or 3-sigma UL
������������������������(s)�� �� ��(s)���� �� (s)
========================================================
white (FC)����99�� �� ����249����������145.8��  19.25 +/- 0.08
white��������������537���� �� 1878��������283.5�� ��20.33 +/- 0.13
u (FC)������������257���� �� 507�������� 245.8���� 18.62 +/- 0.10
u����������������������660���� �� 2003������ 155.6���� 19.91 +/- 0.30
v�������������������� 586���� �� 7371������ 548.8�� ��> 20.29
b����������������������512���� �� 6756����  351.4������21.13 +/- 0.39
uvw1����������������636�������� 7781����  548.8���� > 20.96
uvm2������������ ��611���� �� 7576�� �� 548.9��  > 20.74
uvw2���������� �� 562�������� 7167����  548.8������> 21.06

The values quoted above are not corrected for the expected Galactic 
extinction corresponding to a reddening of E(B-V) = 0.01 mag in the 
direction of the burst (Schlegel et al. 1998).