  No apparent correlation was found between giant pulses (GPs) and X-ray
photons from the Crab pulsar during 5.4 hours of simultaneous observations with
the Green Bank Telescope at 1.5 GHz and Chandra X-Ray Observatory primarily in
the energy range 1.5-4.5 keV. During the Crab pulsar periods with GPs the X-ray
flux in radio emission phase windows does not change more than by +-10% for
main pulse (MP) GPs and +-30% for interpulse (IP) GPs. During giant pulses
themselves, the X-ray flux does not change more than by two times for MP GPs
and 5 times for IP GPs. All limits quoted are compatible with 2-sigma
fluctuations of the X-ray flux around the sets of false GPs with random arrival
times. The results speak in favor of changes in plasma coherence as the origin
of GPs. However, the results do not rule out variations in the rate of particle
creation if the particles that emit coherent radio emission are mostly at the
lowest Landau level.
