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GCN Circular 2115

GRB 030329, color evolution
2003-04-07T18:46:09Z (21 years ago)
Sylvio Klose at TLS Tautenburg <>
A. Zeh, S. Klose (Thueringer Landessternwarte Tautenburg),
A. Henden (USRA/USNO) on behalf of the USNO GRB team and the FUN
   collaboration, and
J. Greiner (MPE Garching),


Stimulated by the recent claim of an appearing supernova (SN) component
(Matheson et al. 2107; Bersier et al., GCN 2109) we have extended our
numerical model (Zeh et al., GCN 2081) by the inclusion of a parameter
which describes a delay, dt, between the onset of the SN and the
GRB and have reanalyzed the USNO data on GRB 030329.

The long-term evolution in the B-V, B-Rc, and V-Rc color of the
optical transient (OT) seen in the high-precision USNO data so far can
indeed be fitted very well with dt approximately 1..2 weeks prior to
the burst, although we cannot reproduce the temporary reddening of the
optical transient which was observed on t=8 days after the burst
(Henden et al., GCN 2110). On day 9 this temporary reddening of the
OT has disappeared. It is well possible that this phenomenon was
related to another episode of flattening of the OTs light curve.

For the sake of clarity we note that the unknown diversity of GRB-SNe
does not allow us to state with certainty that a dt < 0 in our model
does indeed represent a 'SN-first--GRB-later' scenario. So far, this
parameter simply improves the numerical fit if SN 1998bw is used as a
template. Its physical reality remains to be clarified.
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