[AAVSO-HEN] GRB091208B: Swift/UVOT refined analysis

[grb at aavso.org]

The following is a GCN Circular circulated via the AAVSO network.
For an archive and more information on circulars visit:
http://lheawww.gsfc.nasa.gov/docs/gamcosray/legr/bacodine/gcn3_archive.html

TITLE:   GCN CIRCULAR
NUMBER:  10267
SUBJECT: GRB091208B: Swift/UVOT refined analysis
DATE:    09/12/08 18:00:07 GMT
FROM:    Massimiliano de Pasquale at MSSL-UCL  <mdp at mssl.ucl.ac.uk>

  M. De Pasquale (MSSL/UCL) and  C. Pagani (PSU)  report on
behalf of the Swift UVOT team.

  The Swift UltraViolet/Optical Telescope (UVOT) began settled
observations of the GRB 091208B (Swift BAT trigger number 378559;
Pagani et al. GCN Circ. 10256) 119 s after the BAT trigger
with an exposure in the UVOT white filter.

  A new optical source is found at position
RA, Dec = 29.39204, 16.88967, corresponding to

  RA  (J2000) =  01 57 34.09
  Dec (J2000) = +16 53 22.82

This is within 0.6 arseconds from the XRT enhanced position
(Osborne et al., GCN Circ. 10259) and consistent with it.
  The detection is in all 3 filters UVOT used at early epoch.

  The initial magnitudes are given below.

Filter  Time(s)       Mag      Err

wh      119-269      17.92    0.04

b       588-605      18.38    0.29

u       333-583      18.63    0.09

  We caution that data analysis is slightly complicated by the
presence of a dim source 3 arcsecond away from the afterglow.

  The values quoted above are on the UVOT Photometric System
(Poole et al., 2008, MNRAS 383,627). They are not corrected for
the expected Galactic extinction, corresponding to a reddening
of E(B-V)=0.05.