Evidence for Thermal X-Ray Line Emission From the Synchrotron-Dominated Supernova Remnant Rx J1713.7-3946

Abstract

We report the first detection of thermal X-ray line emission from the supernova remnant (SNR) RX J1713.7-3946, the prototype of the small class of syn- -2 -chrotron dominated SNRs. A softness-ratio map generated using XMM-Newton data shows that faint interior regions are softer than bright shell regions. Using Suzaku and deep XMM-Newton observations, we have extracted X-ray spectra from the softest area, finding clear line features at E ph ∼1 keV and ∼1.35 keV. These lines can be best explained as Ne Lyα and Mg Heα from a thermal emission component. Since the abundance ratios of metals to Fe are much higher than solar values in the thermal component, we attribute the thermal emission to reverseshocked SN ejecta. The measured Mg/Ne, Si/Ne, and Fe/Ne ratios of 2.0-2.6, 1.5-2.0, and <0.05 solar suggest that the progenitor star of RX J1713.7-3946 was a relatively low-mass star ( 20 M ⊙ ), consistent with a previous inference based on the effect of stellar winds of the progenitor star on the surrounding medium. Since the mean blastwave speed of ∼6000 km s −1 (the radius of 9.6 pc divided by the age of 1600 yr) is relatively fast compared with other core-collapse SNRs, we propose that RX J1713.7-3946 is a result of a Type Ib/c supernova whose progenitor was a member of an interacting binary. While our analysis provides strong evidence for X-ray line emission, our interpretation of its nature as thermal emission from SN ejecta requires further confirmation especially through future precision spectroscopic measurements using ASTRO-H.

Prospects for Cherenkov Telescope Array Observations of the Young Supernova Remnant RX J1713.7−3946

“…The distance and age of RXJ1713.7−3946 are estimated to be 0.9-1.3kpc and ∼1600yr, respectively (Fukui et al 2003;Moriguchi et al 2005), which is consistent with its connection with the guest star AD393 (e.g., Wang et al 1997). This age estimate is supported by its fast shock velocity (Katsuda et al 2015) and the similarities of its other observed properties to other young SNRs. So far, in comparison with other young shell-type SNRs, the VHE gamma-ray spectrum of RXJ1713.7−3946 is the most precisely measured over a wide energy band (from 0.3 to 100 TeV) thanks to its high brightness.…”

“…We also confirmed that the contamination of the very faint thermal X-ray to the leptonic template and variations of the hadronic template due to the uncertainty of the radio observations are both negligible to the results. Katsuda et al (2015) reported the detection of very faint thermal components, but their spectral analysis region is limited only in the very center of this SNR, with a radius of 5 3. They also presented the softness map, and the analysis is performed on one of the softest regions where the thermal component is brighter than other areas.…”

“…These include lower-energy gamma rays detected by the Fermi Large Area Telescope (Fermi/LAT), synchrotron radio emission and X-rays, and radio line emission from CO molecules and H I gas. Although weak thermal X-ray emission has recently been detected from the SNR interior (Katsuda et al 2015), the X-ray emission is still dominated by synchrotron radiation, which links directly to the existence of high-energy electrons. Radio observations of CO and H I gas have revealed a highly inhomogeneous medium surrounding the SNR, such as clumpy molecular clouds (Fukui et al 2003Fukui 2013;Moriguchi et al 2005;Sano et al 2010Sano et al , 2013Sano et al , 2015.…”

An XMM-Newton Study of the Mixed-morphology Supernova Remnant G346.6-0.2

“…Compared to other X-ray synchrotron emitting SNRs such as Cas A Maeda et al 2009), G1.9+0.3 (Borkowski et al 2010), Kepler (CassamChenaï et al 2004a, RCW 86 (Broersen et al 2014;Tsubone et al 2016), RX J1713 (Lazendic et al 2004;Katsuda et al 2015), SN 1006 (Uchida et al 2013), Tycho (Hwang et al 2002;Eriksen et al 2011), and Vela Jr (Acero et al 2013), we find that G346.6-0.2 exhibits a thermal to non-thermal flux ratio that is nearly an order of magnitude larger that what is seen for the other Xray synchrotron emitting SNRs (see Figure 8). This is in contrasts to that X-ray synchrotron emitting SNRs listed above which have a thermal to non-thermal flux ratio of ∼ 1.…”

H.E.S.S. observations of RX J1713.7−3946 with improved angular and spectral resolution: Evidence for gamma-ray emission extending beyond the X-ray emitting shell

“…It is a prominent and well-studied example of a class of X-ray bright and radio dim (Lazendic et al 2004) shell-type SNRs 1 . The X-ray emission of RX J1713.7−3946 is completely dominated by a non-thermal component (Koyama et al 1997;Slane et al 1999;Cassam-Chenaï et al 2004;Uchiyama et al 2003;Tanaka et al 2008), and in fact, the first evidence for thermal X-ray line emission was reported only recently (Katsuda et al 2015). Despite the past deep H.E.S.S.…”