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Astron. Astrophys. 328, L13-L16 (1997)

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4. Conclusions

We can now summarize the main results of this work:

  1. our observations in B and R bands, probably the earliest to the GRB 970228 event, clearly reveal the fading object (Groot et al. 1997a, van Paradijs et al. 1997) in the intersection of the combined error boxes of GRB 970228 and SAX J0501.7+1146;
  2. they also indicate an increase in luminosity of a factor [FORMULA] 2 on a time scale of 4 hours;
  3. the bulk of the optical event (rising and first decay phase) developed in no more than [FORMULA] ;
  4. the maximum of the optical emission from the `fireball' was attained probably not earlier than [FORMULA] after the [FORMULA] -ray burst;
  5. the ratio [FORMULA] at the supposed optical maximum is [FORMULA] 6 [FORMULA] ;
  6. the R luminosity of the OT at maximum is about 15 times that of the underlying extended object;
  7. our sampling of the source until March 18 shows that after the first there were no new big flares;
  8. the color indices significantly reddened during the month after February 28.

In conclusion, if the optical fading object is the counterpart of GRB 970228, all this severely constrains the modeling of Gamma-Ray Bursts.

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© European Southern Observatory (ESO) 1997

Online publication: March 26, 1998