Orateur
Description
Spectral analysis of X-ray emission from ejecta in supernova remnants (SNRs) is hampered by the low spectral resolution of CCD detectors, which typically creates a degeneracy between the best-fit values of chemical abundances and the plasma emission measure. The combined contribution of shocked ambient medium and ejecta to the emerging X-ray emission further complicates the determination of the ejecta mass and chemical composition. This degeneracy leads to big uncertainties in mass estimates and can introduce a bias in the comparison between the ejecta chemical composition derived from the observations and the yields predicted by explosive nucleosynthesis models. An analogous degeneracy between the nonthermal and thermal continuum emission hampers precise estimates of the X-ray thermal and nonthermal fluxes in regions close to the shock fronts.
We explored the capabilities of newAthena/XIFU on identifying a spectral feature that may allow us to discriminate between metal-rich and pure-metal plasmas in X-ray spectra of SNRs. We investigated spectral features of bremsstrahlung, radiative recombination continua (RRC), and line emission, by exploring a wide range of chemical abundances, plasma temperatures, and ionisation parameters.
We then synthesized NewAthena/XIFU spectra from a state-of-the-art 3D hydrodynamic simulation of Cas A and identified the southeastern Fe-rich clump of Cas A as an ideal target to apply our diagnostic tool. The analysis of the synthetic spectra highlights that a bright RRC shows up in the spectra when the plasma is made of pure-metal ejecta and a comparison with the current CCD spectra clearly shows how such feature is
missed because of the low spectral resolution. Thanks to NewAthena, we will be able to pinpoint the presence of pure-metal ejecta in the X-ray spectra of SNRs, critical to recover the absolute mass and chemical composition of the ejecta. Moreover, we found that thanks to the superior spectral resolution we will significantly improve the constraints on the thermal emission parameters retrievable from emission lines diagnostic enabling a more precise estimate of the nonthermal-to-thermal flux ratio.
