Discovery of recombining plasma in the supernova remnant 3C 391

Abstract

Recent X-ray study of middle-aged supernova remnants (SNRs) reveals strong radiative recombination continua (RRCs) associated with overionized plasmas, which origin still remains uncertain. We report a discovery of an RRC in the middle-aged SNR 3C 391. If the X-ray spectrum is fitted with a two-temperature plasma model in collisional ionization equilibrium (CIE), residuals of a Si XIV Lyα line at 2.006 keV, a S XVI Lyα line at 2.623 keV and the edge of a RRC of Si XIII at 2.666 keV are found. In fact, the X-ray spectrum is well described by the composite model consisting of the CIE plasma and a recombining plasma (RP). The abundance pattern suggests that the RP is due to ejecta from core-collapse supernova of the progenitor mass of about 15 M . There is no significant difference of the recombining parameters between the south-east region and the north-west region surrounded by dense molecular clouds. We also find a hint of a Fe I Kα line at 6.4 keV (2.4 σ detection) from the south-east region of the SNR.

Comparing Neutron Star Kicks to Supernova Remnant Asymmetries

“…Using a deep Chandra observation, Chen et al (2004) found that its X-ray emission is best described using a NEI plasma with approximately solar abundances of Mg, Si and S, and a uniform temperature throughout the SNR of kT ≈ 0.2 keV approaching CIE. Follow-up observations using Suzaku further confirmed the presence of a near-CIE plasma; however, Sato et al (2014) found that the X-ray spectrum of 3C 391 requires an additional high-temperature (kT ≈ 0.50 keV) recombining plasma (RP) component. The detection of enhanced Ca led Sato et al (2014) to suggest that the RP component arises from ejecta from a 15M progenitor, and its high ionization timescale (n e t ≈ 10 12 s cm −3 ) makes it one of the only SNR that shows evidence of overionization whose plasma is in/close to ionization equilibrium.…”

“…Two 1720 MHz OH masers (Frail et al 1996b) as well as enhanced CO (Wilner et al 1998) and [Oi] (Reach & Rho 1996) emission is seen along the shell, evidence that the remnant is interacting with a nearby molecular cloud (e.g., Reach & Rho 1999). 3C 391 has been studied in X-rays using Einstein (Wang & Seward 1984), ROSAT (Rho & Petre 1996), ASCA (Chen & Slane 2001), Chandra (Chen et al 2004) and Suzaku (Sato et al 2014). These observations revealed a center-filled morphology characteristic of mixed-morphology SNRs (Rho & Petre 1998).…”

First discovery of iron line emission generated by low-energy cosmic rays

“…First discovery of iron line emission generated by low-energy cosmic rays K. K. Nobukawa of LECRs with the 6.40 keV line should be valid for SNRs. In fact, analyzing the Suzaku data of 3C391 and Kes79, [14,15] reported detection of the 6.40 keV line which would originated from LECRs. We expanded the search for the 6.40 keV line to other SNRs located in the eastern region of the Galactic ridge, where 3C 391 and Kes 79 are located.…”

The effects of X-ray background on the X-ray emission from the Galactic supernova remnants

“…Analysing the extended and faint sources, such as the Galactic supernova remnants (SNRs), with accurately modelled background emission is important since it might affect the spectral results (e.g., [1,2,3]). The location of an SNR in the sky (e.g., Galactic latitude) is critical for the background estimation, which will define the model fraction of the cosmic X-ray background (CXB), the Galactic ridge X-ray emission (GRXE), or the foreground emission (FE) (see Figure 1 for a simulated projection 1 ).…”

“…The location of an SNR in the sky (e.g., Galactic latitude) is critical for the background estimation, which will define the model fraction of the cosmic X-ray background (CXB), the Galactic ridge X-ray emission (GRXE), or the foreground emission (FE) (see Figure 1 for a simulated projection 1 ). Moreover, in recent years, the importance of background modelling before performing detailed spectral analysis has been emphasised in plenty of studies (e.g., [3,4,5,6]). Under these circumstances, all spectral parameters can be examined reliably with the background modelling method, which is suitable for determining the thermal or nonthermal characteristics of SNRs.…”