New Publication: “Evidence for Thermal X-Ray Emission from the Synchrotron-dominated Shocks in Tycho’s Supernova Remnant” by Amaël Ellien et al.

Young supernova remnant (SNR) shocks are believed to be the main sites of galactic cosmic-ray production, showing X-ray synchrotron-dominated spectra in the vicinity of their shock. While a faint thermal signature left by the shocked interstellar medium (ISM) should also be found in the spectra, proofs for such an emission in Tycho’s SNR have been lacking. We perform an extended statistical analysis of the X-ray spectra of five regions behind the blast wave of Tycho’s SNR using Chandra archival data. We use Bayesian inference to perform extended parameter space exploration and sample the posterior distributions of a variety of models of interest. According to Bayes factors, spectra of all five regions of analysis are best described by composite three-component models taking nonthermal emission, ejecta emission, and shocked ISM emission into account. The shocked ISM stands out the most in the northern limb of the SNR. We performed an extended analysis of the northern limb and show that the measured synchrotron cutoff energy is not well constrained in the presence of a shocked ISM component. Such results cannot currently be further investigated by analyzing emission lines in the 0.5–1 keV range, because of the low Chandra spectral resolution in this band. We show with simulated spectra that Athena X-ray Integral Field Unit future performances will be crucial to address this point.

Left: broadband Chandra image of Tycho’s SNR. Right: schematic view of Tycho’s SNR. The five black boxes are the regions over which our shock spectra were extracted and analyzed. The contours are drawn from the contrast image computed from the normalized 1.7–1.95 keV and 4.0–6.0 keV images. Note that the contrast image has been smoothed with a 1σ Gaussian kernel before drawing the contours.

Full Article:
Ellien, A. (SHARP), Greco, E. (SHARP) and Vink, J. (SHARP) (2023). Evidence for Thermal X-Ray Emission from the Synchrotron-dominated Shocks in Tycho’s Supernova Remnant. The Astrophysical Journal, 951, doi: 10.3847/1538-4357/accc85

License: CC BY 4.0