Constraints on the optical precursor to the naked-eye burst GRB080319B
  from Pi of the Sky observations
  I present the results of the search for an optical precursor to the naked-eye
burst - GRB080319B, which reached 5.87m optical peak luminosity in the "Pi of
the Sky" data. A burst of such a high brightness could have been preceded by an
optical precursor luminous enough to be in detection range of our experiment.
The "Pi of the Sky" cameras observed the coordinates of the GRB for about 20
minutes prior to the explosion, thus provided crucial data for the precursor
search. No signal within 3 sigma limit was found. A limit of 12m (V-band
equivalent) was set based on the data combined from two cameras, the most
robust limit to my knowledge for this precursor.
