Speaker
Description
One of the most promising candidates in the universe for the r-process r-process, which is the only sites that can provide elements heavier than $\mathrm{^{209}Bi}$ are the binary neutron-star mergers (NSMs).The post-merger remnant becomes optically thin in a few weeks to months, and gamma-rays from the decay of r-process elements are observable in the MeV energy band. The presence of r-process nuclei in NSMs was already shown by the infrared observation of the first NSM gravitational event GW170817 (e.g.,Kasen et al.2017;Roswog et al.2018;Domoto et al.2022), and such MeV gamma-rays are expected carry more direct information on the r-process nuclei especially for Lanthanoids.In fact,however ,nuclear gamma-rays from NSMs are so dim that they are below sensitivity in the MeV missions. (Hotokezaka et al. 2016).
According to numerical estimation of gamma-rays from NSMs (Terada et al 2022), they have unique gamma-ray spectra compared with other high energy objects and thus the spectral shape can be used to identify NSMs.Numerically, Terada et al.(2022) provides a new method to identify of NSMs using color-color diagram both in the hard Xray (10-500 keV) and gamma-ray (70-3000 keV) bands.
In this study, we searched for NSM remnants at the galactic center region ($-15^{\circ}
