  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 a SN into a young
supernova remnant. To date, the X-ray emission has been dominated by the
shocked circumstellar medium (CSM), 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 XRISM-Resolve high resolution
spectrometer in pinpointing signatures of the shocked ejecta in SN 1987A.
Taking advantage of a self consistent state-of-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.
