NuSTAR Observations of the Supernova Remnant RX J1713.7-3946

The shock waves of supernova remnants (SNRs) are prominent candidates for the acceleration of the Galactic cosmic rays. SNR RX J1713.7-3946 is one well-studied particle accelerator in our Galaxy because of its strong nonthermal X-ray and gamma-ray radiation. We have performed Nuclear Spectroscopic Telescope Array (3-79 keV) observations of the northwest rim of RX J1713.7-3946, which is the brightest part in X-ray and has a shock speed of about 4000 km s(-1). The spatially resolved X-ray emission from RX J1713.7-3946 is detected up to 20 keV for the first time. The hard X-ray image in 10-20 keV is broadly similar to the soft-band image in 3-10 keV. The typical spectrum is described by power-law model with exponential cutoff with the photon index Gamma= 2.15 and the cutoff energy epsilon(c) = 18.8 keV. Using a synchrotron radiation model from accelerated electrons in the loss-limited case, the cutoff energy parameter ranges from 0.6-1.9 keV, varying from region to region. Combined with the previous measurement of the shock speed, the acceleration of electrons is close to the Bohm-limit regime in the outer edge, while the standard picture of accelerated particles limited by synchrotron radiation in SNR shock is not applicable in the inner edge and the filamentary structure