TITLE:   GCN CIRCULAR
NUMBER:  6331
SUBJECT: GRB 070420: NIR and optical afterglow confirmed
DATE:    07/04/20 07:18:55 GMT
FROM:    Stefano Covino at Brera Astronomical Observatory  <stefano.covino@brera.inaf.it>

P. D'Avanzo, L.A. Antonelli, L. Calzoletti, S. Campana, G.  
Chincarini, M.L. Conciatore, S. Covino, S. Cutini, P. D'Avanzo, V.  
D'Elia, F. Dalessio, F.  Fiore, D. Fugazza, P. Goldoni, D. Guetta, C.  
Guidorzi, G.L. Israel,  D. Malesani, N. Masetti, A. Melandri, E.  
Meurs, L. Nicastro, E. Palazzi, E. Pian, S. Piranomonte, D. Rizzuto,  
L.  Stella, G. Stratta, G. Tagliaferri, G. Tosti, V. Testa, S.D.  
Vergani,  F. Vitali report on behalf of the REM team:


We observed the field of the GRB 070420 (Stamatikos et al. GCN 6330)  
with the robotic 60-cm REM telescope located at La Silla (Chile). A   
set of observations was performed automatically in the optical and  
near infrared filters (V, R, I and J, H, K, z) starting on 2007 April  
20 at 06:19:32 UT, 42s after the Swift trigger and 79s after the GRB  
time.

Although the observations were performed under thin clouds and at  
very high airmass (~ 7.5) we clearly detect the NIR and optical  
afterglow at the coordinates reported by UVOT (GCN 6330).

Preliminary analysis gives an approximate magnitude about 5 minutes  
after the burst time was H  = 13.1 +/- 0.2.

Observations were then soon interrupted due to excessive airmass.

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