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Abstract:

The X-ray astronomy satellite XRISM, successfully launched in September 2023, is already providing valuable insights into the long-standing mystery of supernova explosion mechanisms. Our recent study of a nearby supernova remnant, Cassiopeia A, suggests that the internal structure of massive stars becomes unstable during the final decade before core-collapse, potentially leading to significant mass ejection --- a behavior unexpected from standard stellar evolution models. Direct evidence of such pre-explosion activity requires prompt follow-up observations within ~10 days of the supernova event. Since core-collapse supernovae emit a burst of precursor neutrinos prior to the explosion, these neutrinos can serve as an early warning to trigger immediate observations. Super-Kamiokande (SK), currently in operation, has the sensitivity to detect such neutrino bursts from supernovae occurring within our Galaxy or nearby satellite galaxies such as the Magellanic Clouds. However, due to SK’s limited angular resolution (a few degrees in radius), wide-field instruments are essential for effective localization. We propose to utilize Xtend, the wide-field soft X-ray imager onboard XRISM, for such rapid-follow-up observations. Xtend offers the largest field of view and effective area ever achieved for a single-focus X-ray imaging satellite, enabling a standby observation triggered by a neutrino alert. In this presentation, we outline the scientific goals and observational strategy of this novel program, and discuss in detail the technical coordination between Super-Kamiokande and XRISM/Xtend for real-time, multi-messenger observations of nearby supernovae.