Search for a correlation between giant radio pulses and hard X-ray emissions in the Crab pulsar

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.