X-Ray Hotspots in the Northwest Shell of the Supernova Remnant RX J1713.7-3946

Abstract

The supernova remnant (SNR) RX J1713.7-3946 is one of the best-studied accelerators of cosmic rays because of its strong nonthermal X-ray and gamma-ray radiation. We have analyzed accumulated Chandra observations with a total exposure time of ∼266 ks in the northwest rim of RX J1713.7-3946. We detect a substantially large number of point-like sources, referred to as "hotspots," which are likely associated with the remnant. The spectra of the hotspots are well described by an absorbed power-law model. The spectral properties ( ${10}^{21}\ {\mathrm{cm}}^{-2}\lesssim {N}_{{\rm{H}}}\,\lesssim {10}^{23}\ {\mathrm{cm}}^{-2}$ and 0.5 ≲ Γ ≲ 6) are different from diffuse X-ray emission in RX J1713.7-3946, and the harder hotspot tends to have the larger N_H. We also confirm yearly and monthly variabilities of flux for some hotspots. We propose that RX J1713.7-3946 is embedded in a complex surroundings where some dense molecular clumps and cores exist inside a wind-blown cavity, and that the hotspot traces synchrotron emission caused by an interaction of shock waves of the SNR and dense molecular cores with a number density of 10⁵-10⁷ cm^-3. The X-ray radiation of the hotspot might be emitted both from primary electrons accelerated at the shocks and secondary electrons produced by the interaction of accelerated protons with the cores.