XMM-Newton observations of the supernova remnant RX J1713.7-3946 and its central source

Abstract

We present new results from the observations of the supernova remnant (SNR) RX J1713.7-3946 (also G347.3-0.5) performed in five distinct pointings with the EPIC instrument on board the satellite XMM-Newton. RX J1713.7-3946 is a shell-type SNR dominated by synchrotron radiation in the X-rays. Its emission (emission measure and photon index) as well as the absorption along the line-of-sight has been characterized over the entire SNR. The X-ray mapping of the absorbing column density has revealed strong well-constrained variations (0.4 × 10²² cm^-2 ≤ N_H ≤ 1.1 × 10²² cm^-2) and, particularly, a strong absorption in the southwest. Moreover, there are several clues indicating that the shock front of RX J1713.7-3946 is impacting the clouds responsible for the absorption as revealed for instance by the positive correlation between X-ray absorption and X-ray brightness along the western rims. The CO and HI observations show that the inferred cumulative absorbing column densities are in excellent agreement with the X-ray findings in different parts of the remnant on condition that the SNR lies at a distance of 1.3 ± 0.4 kpc, probably in the Sagittarius galactic arm, instead of the commonly-accepted value of 6 kpc. An excess in the CO emission is found in the southwest suggesting that the absorption is due to molecular clouds. A search for OH masers in the southwestern region has been unsuccessful, possibly due to the low density of the clouds. The X-ray mapping of the photon index has also revealed strong variations (1.8 ≤ Γ ≤ 2.6). The spectrum is steep in the faint central regions and flat at the presumed shock locations, particularly in the southeast. Nevertheless, the regions where the shock impacts molecular clouds have a steeper spectrum than those where the shock propagates into a low density medium. The search for the thermal emission in RX J1713.7-3946 has been unsuccessful leading to a number density upper limit of 2 × 10^-2 cm^-3 in the ambient medium. This low density corresponds to a reasonable kinetic energy of the explosion provided that the remnant is less than a few thousand years old. A scenario based on a modified ambient medium due to the effect of a progenitor stellar wind is proposed and leads to an estimate of RX J1713.7-3946's progenitor mass between 12 and 16 M_⊙. The X-ray bright central point source 1WGA J1713.4-3949 detected at the center of SNR RX J1713.7-3946 shows spectral properties very similar to those of the Compact Central Objects found in SNRs and consistent in terms of absorption with that of the central diffuse X-ray emission arising from the SNR. It is highly probable that the point source 1WGA J1713.4-3949 is the compact relic of RX J1713.7-3946's supernova progenitor.