NuSTAR observation of the Vela pulsar and its nebula

We present the analysis of 200-ks NuSTAR observation of the Vela pulsar and the pulsar wind nebula (PWN). The phase-resolved spectra corresponding to two main peaks in the folded pulse profile differ significantly. The spectrum of Peak 1 is significantly harder than that of Peak 2 in qualitative agreement with the earlier RXTE results. However, for both spectra, the values of power-law (PL) fit photon indices are noticeably larger than the previously reported values. The harder (Peak 1) spectrum has a photon index of $1.06\pm0.16$ which is close to those measured for the bright inner jets of the PWN. We used the off-pulse interval to remove the emission from the pulsar and measure the compact pulsar wind nebula (PWN) spectrum in hard X-rays. We also measured the spectrum from the south-western (SW) region of the PWN which is resolved by NuSTAR from the compact PWN. For both regions, we fit the NuSTAR spectra by themselves and together with the Chandra X-ray Observatory spectra. We found that the PWN spectrum (for both regions) requires a more complex model than a simple PL. The fits to compact PWN spectrum favor exponentially cutoff PL model, with the cutoff energy of about 50 keV, over the broken PL model. The observed synchrotron photon energies imply electrons accelerated to about 150 TeV.