XMM-Newtonobservations of the supernova remnant RX J1713.7–3946 and its central source

Abstract

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 shelltype 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 × 10 22 cm −2 ≤ N H ≤ 1.1 × 10 22 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 H 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.

Study of TeV shell supernova remnants at gamma-ray energies

“…It is surprising that RCW 86, where part of the shock emits thermal X-rays that trace ambient medium densities of ∼0.5 cm −3 , shows a similar HE spectral index to RX J1713.7−3946 where no thermal X-ray emission has been detected so far and where the density upper limit is very constraining (<0.02 cm −3 , Cassam-Chenaï et al 2004). Because of the density difference, we could have expected a higher fraction of hadronic emission in RCW 86 and thus a steeper spectral index at HE.…”

High-energy particle acceleration in the shell of a supernova remnant

“…The CO data 22 suggest that a cloud is interacting with the northwestern part of the SNR, where a striking spatial coincidence between the CO density peaks and the regions of peak X-ray emission is seen. The X-ray data 23 also indicate significant absorption column densities in the western part of the remnant, at values about twice those to the east. These indications fit qualitatively with the γ-ray image presented here, where TeV emission is seen from the whole SNR shell but with an increased flux from the northwestern side.…”

“…Given the recent estimates [22][23][24] of the distance to the source of 1 kpc, if a significant part of the TeV flux were to be formed by interactions of cosmic-ray nuclei with gas atoms in the cloud with density n exceeding 100 cm −3 , the energetics implied by the γ-ray flux and the spectrum would be a few times 10 49 n −1 erg between 10 and 100 TeV. This is consistent with the picture of an SNR origin of Galactic cosmic rays involving about 10% efficiency for conversion of the mechanical energy of the explosion into non-thermal particles, and a production spectrum in the SNR which is approximately an E −2 power law from several GeV to about one PeV.…”

Nonthermal and thermal emission from the supernova remnant RX J1713.7-3946

“…Subsequent studies of this SNR with the ASCA satellite by Koyama et al (1997) and Slane et al (1999), and later with XMM by Cassam-Chenaï et al (2004), have not positively identified any thermal X-ray emission so they tentatively concluded that the observable X-ray emission is entirely nonthermal.…”