NuSTAR hard X-ray spectra of radio galaxies
  NuSTAR observatory, with its 3 - 78 keV broadband spectral coverage, enables
the detections of the high-energy cutoff in a number of active galaxies,
including several individual radio loud ones. In this work we present
systematic and uniform analyses of 55 NuSTAR spectra for a large sample of 28
radio galaxies, 20 of which are FR II galaxies. We perform spectral fitting to
measure the high energy cut-off $E_{cut}$, photon index $\Gamma$, reflection
factor R and Fe K$\alpha$ line equivalent width. Measurements of $E_{cut}$ are
given for 13 sources, and lower limits for the rest. We find those $E_{cut}$
non-detections could primarily be attributed to the obviously smaller net
photon counts in their spectra. This indicates that the NuSTAR spectra of the
majority of our sample are dominated by the thermal corona emission, and the
$E_{cut}$ distribution of the sample is indistinguishable from that of a radio
quiet one in literature. The flatter NuSTAR spectra we observed, comparing with
radio quiet sources, are thus unlikely due to jet contamination. The radio
galaxies also show weaker X-ray reflection (both in R and Fe K$\alpha$ line EW)
comparing with radio quiet ones. Combining with the radio quiet sample we see a
correlation between R and EW, but with considerably large scatter. Notably, the
radio loud and quiet sources appear to follow a common $\Gamma$ - R correlation
trend, supporting the outflowing corona model for both populations in which
higher bulk outflowing velocity yields weaker reflection and flatter X-ray
slope.
