A search for thermal X-ray emission from the composite supernova remnant G21.5–0.9 with Suzaku

Abstract

G21.5–0.9 is a young plerionic composite supernova remnant (SNR) hosting a bright pulsar wind nebula. The previous X-ray studies reported that the X-ray spectrum of the entire SNR can be fitted with a non-thermal spectral model, while the recent Chandra studies have pointed out that its X-ray spectrum also shows weak thermal emission. With this motivation, we search for a feature of the thermal emission from the SNR using the high spectral resolution of Suzaku X-ray Imaging Spectrometer data observed in 2007 and 2009. We found that both a pure non-thermal model and a non-thermal plus thermal model yield statistically acceptable fits. The two-component X-ray spectrum gives a photon index of ∼ 1.92 and an electron temperature of ∼ 0.2 keV, and an ionization time-scale of more than 4 × 10 12 cm −3 s. We also performed XRISM and Athena simulations of the same region on the SNR to investigate any sign of thermal emission. Our simulations show the potential of the future missions Athena and XRISM for revealing the thermal emission from G21.5–0.9, where the elemental lines of Ne, Mg, and Si can be well traced.