TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  2345
SUBJECT: XRF 030723: Detection of a rebrightening in the optical afterglow 
DATE:    03/08/06 18:38:00 GMT
FROM:    Jens Hjorth at U.Copenhagen  <jens@astro.ku.dk>

J. P. U. Fynbo (U. Aarhus), J. Hjorth (U. Copenhagen), J. Gorosabel 
(IAA-CSIC/STScI), B. L. Jensen (U. Copenhagen), M. I. Andersen (AIP), 
R. A. M. J. Wijers (U. Amsterdam), C. Kouveliotou (NASA/MSFC), on behalf 
of GRACE, report:

"We have monitored the afterglow of XRF 030723 (Prigozhin et al. GCN #2313; 
Fox et al. GCN #2323; Butler et al. GCN #2328) with the ESO VLT. Between 
Aug 3.2 UT and Aug 6.3 2003 UT the optical afterglow brightened by 1.0 mag 
to R ~ 24.3. If this is due to the emergence of a supernova it would 
strengthen the link between GRBs and XRFs. It would also indicate a fast rise 
for the supernova and a relatively low redshift for XRF 030723, z < 1, 
consistent with the earlier spectroscopic constraints (Fynbo et al. 
GCN #2327). Alternatively, we may be seeing a rebrightening due to late 
energy injection (refreshed shock). Continued spectroscopic and photometric 
monitoring is planned. 

Images are posted at http://www.astro.ku.dk/~brian_j/grb/grb030723

We thank the Paranal Observatory staff for efficiently conducting the
reported service-mode observations."