  We present the results of the search for a correlation between giant radio
pulses (GRPs) at 1.4 GHz and hard X-rays at 15-75 keV from the Crab pulsar. We
made simultaneous ground and satellite observations of the Crab pulsar over 12
hours in three occasions in April 2010, March and September 2011, and got a
sample of 1.3*10^4 main-pulse phase GRPs. From these samples we have found
statistically marginal enhancement (21.5%, 2.70 sigma) of hard X-ray flux
within +/- 1.5 degree phase angle of the synchronous peak of main-pulse phase
GRPs. This enhancement, if confirmed, implicates that GRPs may accompany plasma
density increases in the pulsar magnetosphere.
