GCN Circular 413

Optical Observations of GRB990907

E. Palazzi, E. Pian, N. Masetti, F. Frontera (ITESRE, CNR, Bologna), 
P.M. Vreeswijk, E. Rol (U. of Amsterdam), H. Pedersen, J. Hjorth (CUO,
Copenhagen), J. van Paradijs (U. of Amsterdam and U. of Alabama in
Huntsville), C. Kouveliotou (NASA-MSFC/USRA), P. Leisy, A. Pizzella, 
E. Pompei (ESO-La Silla), R. Mennickent (Univ. de Concepcion, Chile),
C.G. Tinney, F. Freeman, S. Lee, J. Hawthorn (AAO), R. McMahon, S. Maddox,
C. Singleton (IoA, Cambridge), and H. Jones (RSAA), on behalf of the
BeppoSAX and Amsterdam/Huntsville GRB optical follow-up teams, report:

"We obtained V band images of the GRB 990907 field (GCN #405
Not found
 
 
 and 
GCN #409
Not found
 
 
) at the Anglo Australian Telescope with Taurus + MITLL2, 
at the ESO 1.54m Danish telescope with DFOSC, and at the ESO VLT telescope
with FORS1, beginning 24.9 hrs after the GRB event. Images in other bands 
(R and I) were also acquired as detailed in the following table: 


  Telescope   Date (UT)     Filter   Exptime    Limit mag.   Seeing
						(3-sigma)     

    AAT      Sep  8.7698      V      480 sec      23.2        1".4
   Danish    Sep  9.3736      V     1600 sec      23.0        2".6
   Danish    Sep  9.3755      R     1600 sec      23.0        2".6
   Danish    Sep  9.3854      I     1600 sec      22.5        3".5
    AAT      Sep 10.7806      V      800 sec      22.7        2".8
    VLT      Sep 10.4111      V      180 sec      23.5        1".1
    VLT      Sep 10.4153      R      180 sec      23.6        1".1
    AAT      Sep 18.3736      V      960 sec      23.2        2".2


Photometric calibration was done using standard stars in the Landolt
field PG0231+051. Comparisons were made among the V, R, and I band
images with the Digital Sky Survey, between the two R and among the 
five V frames taken at different epochs.
The comparison does not show any object with significant brightness
variations larger than 0.3 mag.


This message can be cited."