The 1st IReNA-Ukakuren Joint Workshop “Advancing Professional Development in Nuclear Astrophysics and Beyond”

Feasibility studies to detect r-process nuclear emissions from the binary-neutron-star merger remnants with the HEX-P satellite

31 Aug 2023, 13:50

5m

Large Seminar Room (Subaru Building) (NAOJ (National Astronomical Observatory of Japan))

Poster Poster Session

Speaker

Mr Motogami Yugo (Saitama Univ.)

Description

The r-process nucleosynthesis site in the Universe is one of the important astrophysical questions. The r-process site should be a neutron-rich environment, and the binary neutron-star mergers (NSMs) are considered to be the most promising site. Nuclear gamma rays through the decay of unstable nuclei will provide direct evidence of r-process synthesis. However, the gamma-ray radiation is extremely weak (Hotokezaka et al., 2016), and the sensitivity of the near future MeV missions is limited to detect gamma-rays from NSMs at Mpc distances or NSM remnants in our Galaxy (Terada et al., 2022).

In this study, we focus on the hard X-ray band, which enables us to detect K X-rays emitted through the decay chain of r-process nuclei. Here, we performed the feasibility study to detect NSMs with the next-generation US-lead hard-X-ray mission, HEX-P. The mission is proposed to have the large effective area (4400 $\mathrm{c}\mathrm{m}$${}^2$) in the soft to hard X-ray bands (2-200 $\mathrm{k}\mathrm{e}\mathrm{V}$). As demonstrated in Terada et al. (2022), the NSM is expected to have a unique spectral shape compared with other high-energy sources. Therefore, we examined the slope of the energy spectra simulated for NSMs in the 2-200 $\mathrm{k}\mathrm{e}\mathrm{V}$ band. Accordingly, we performed an observation simulation with the exposure of 1 Ms to investigate the ratio of (25-70 $\mathrm{k}\mathrm{e}\mathrm{V}$)/(2-25 $\mathrm{k}\mathrm{e}\mathrm{V}$) and (70-200 $\mathrm{k}\mathrm{e}\mathrm{V}$)/(25-70 $\mathrm{k}\mathrm{e}\mathrm{V}$) fluxes. We used the same nuclear model in Terada et al. (2022), but with X-ray irradiation data from the daughter nuclei of r-process nuclei. As a result, the NSM can be distinguished from other sources with at least 3$\sigma$ significance for the age of up to ${10}^4$ $\mathrm{y}\mathrm{e}\mathrm{a}\mathrm{r}\mathrm{s}$ within a distance of 100 $\mathrm{p}\mathrm{c}$. In this presentation, we will discuss the feasibility to detect nuclear gamma-rays lines with the HEX-P for gamma-ray diagnostics in the neutron environment.

Presentation materials

Ukakuren_poster_presentation_No.3motogami.pdf