[AAVSO-HEN] GRB 091208B: Faulkes Telescope North and South Optical Afterglow

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TITLE:   GCN CIRCULAR
NUMBER:  10262
SUBJECT: GRB 091208B: Faulkes Telescope North and South Optical Afterglow
DATE:    09/12/08 13:52:33 GMT
FROM:    Zach Cano at ARI/John Moores Liverpool  <zec at astro.livjm.ac.uk>

Z. Cano, A. Melandri, C.G. Mundell (Liverpool JMU), A. Gomboc (U.
Ljubljana), D. Bersier, N.R. Clay, S. Kobayashi, C.J. Mottram, R.J. Smith,
I.A. Steele (Liverpool JMU), C. Guidorzi (U. Ferrara) report on behalf of
a large collaboration:

The 2-m Faulkes Telescopes North and South robotically followed up 
GRB091208B (SWIFT trigger 378559; Pagani et al. GCN 10256) beginning 1.78
min after the GRB trigger time.  We detect the optical afterglow in BRi'
filters at the location reported by de Ugarte Postigo et al. (GCN 10255)
and Pagani et al. (GCN 10256).

We derive the following preliminary magnitudes wrt USNOB1:

Filter    Mag     Merr      T-To (s)
-------------------------------------------
  R      17.75    0.02      572
  R      18.48    0.03     1656
  I      17.51    0.05     1036
  I      18.34    0.04     3749

>From our observations we derive a power-law decay constant of ~ 0.6 for
both filters.

We have not corrected our magnitudes for the small amount of foreground
reddening along the line of sight (E(B-V) = 0.05, corresponding to Av =
0.17 (Schlegel et al. 1998)).

Observations and analysis are ongoing.

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