Probing Shocked Ejecta in SN 1987A: A Novel Diagnostic Approach Using XRISM-Resolve

Supernova (SN) 1987A is one of the best candidates to exploit the capabilities of the freshly launched XRISM satellite. This celestial object offers the unique opportunity to study the evolution of an SN into a young supernova remnant. To date, the X-ray emission has been dominated by the shocked circumstellar medium, with no shocked ejecta firmly detected. However, recent studies provide compelling evidence that in the forthcoming years, the X-ray emission from SN 1987A will increasingly stem from the ejecta. Our aim is to assess the proficiency of the XRISM-Resolve high-resolution spectrometer in pinpointing signatures of the shocked ejecta in SN 1987A. Taking advantage of a self-consistent state-of-the-art magneto-hydrodynamic simulation that describes the evolution from SN 1987A to its remnant, we synthesized the XRISM-Resolve spectrum of SN 1987A, as it would be collected in the allocated observation during the performance verification phase, which is foreseen for 2024. Our predictions clearly show the leading role of shocked ejecta in shaping the profile of the emission lines. The Doppler broadening associated with the bulk motion along the line of sight of the rapidly expanding ejecta is shown to increase the line widths well above the values observed so far. The quantitative comparison between our synthetic spectra and the XRISM spectra will enable us to establish a strong connection between the broadened line emission and the freshly shocked ejecta. This, in turn, will allow us to retrieve the ejecta dynamics and chemical composition from the X-ray emission.