TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  4677
SUBJECT: GRB 060204B: BVRi-band detections of optical afterglow 
DATE:    06/02/05 18:12:58 GMT
FROM:    Javier Gorosabel at IAA-CSIC  <jgu@laeff.inta.es>

J.P.U. Fynbo, J. Gorosabel(*), B.L. Jensen (DARK Cosmology Centre),
Jyri Naeraenen (Helsinki Observatory) report on behalf of a larger 
collaboration:

"We have acquired BVRi-band images (3x300s in each band) of the Swift
GRB 060204B (Trigger number 180241, GCNs #4655, #4669) optical
afterglow (GCN #4661). The source is clearly detected in VRi, and
barely in B. We derive a rough magnitude of R=22.5 on Feb 5.07 UT
(vs. USNOB1). Considering the R=20.4 mag value on Feb. 4.64 UT (as
reported in GCN #4661) we estimate a slow-fading decay index alpha 
~-0.8. Our B-band detection imposes a conservative maximum redshift
 of z ~< 4.

A finding chart of the R-band afterglow can be found at:

 http://www.dsri.dk/~jgu/grb060204B/FCs/grb060204B.NOT.R.gif

This message can be cited."


(*) Visitor at DARK cosmology centre. Default affiliation; IAA-CSIC, 
    Granada.