To search for giant X-ray pulses correlated with the giant radio pulses ( GRPs ) from the Crab pulsar , we performed a simultaneous observation of the Crab pulsar with the X-ray satellite Hitomi in the 2 – 300 keV band and the Kashima NICT radio observatory in the 1.4 – 1.7 GHz band with a net exposure of about 2 ks on 25 March 2016 , just before the loss of the Hitomi mission .
The timing performance of the Hitomi instruments was confirmed to meet the timing requirement and about 1,000 and 100 GRPs were simultaneously observed at the main and inter-pulse phases , respectively , and we found no apparent correlation between the giant radio pulses and the X-ray emission in either the main or inter-pulse phases .
All variations are within the 2 sigma fluctuations of the X-ray fluxes at the pulse peaks , and the 3 sigma upper limits of variations of main- or inter- pulse GRPs are 22 % or 80 % of the peak flux in a 0.20 phase width , respectively , in the 2 – 300 keV band .
The values become 25 % or 110 % for main or inter-pulse GRPs , respectively , when the phase width is restricted into the 0.03 phase .
Among the upper limits from the Hitomi satellite , those in the 4.5-10 keV and the 70-300 keV are obtained for the first time , and those in other bands are consistent with previous reports .
Numerically , the upper limits of main- and inter-pulse GRPs in the 0.20 phase width are about ( 2.4 and 9.3 ) \times 10 ^ { -11 } erg cm ^ { -2 } , respectively .
No significant variability in pulse profiles implies that the GRPs originated from a local place within the magnetosphere and the number of photon-emitting particles temporally increases .
However , the results do not statistically rule out variations correlated with the GRPs , because the possible X-ray enhancement may appear due to a > 0.02 % brightening of the pulse-peak flux under such conditions .