Thermal and kinematic properties of ejecta in SN1987A revealed by XRISM

Abstract

We present an analysis of high-resolution spectra from the shock-heated plasmas in SN 1987A, based on an observation using the Resolve instrument onboard the X-Ray Imaging and Spectroscopy Mission (XRISM). The 1.7–10 keV Resolve spectra are accurately represented by a single component, plane parallel shock plasma model, with a temperature of 2.84⁺⁰.⁰⁹ -₀.₀₈ keV and an ionization parameter of 2.64⁺⁰.⁵⁸ -₀.₄₅ × 10¹¹ s cm⁻³. The Resolve spectra are also well reproduced by the 3-D magneto hydrodynamic simulation presented by Orlando et al. (2020) suggesting substantial contribution from the ejecta. The metal abundances obtained with Resolve align with the LMC value, indicating that the X-rays in 2024 originate from non-metal-rich shock-heated ejecta and the reverse shock has not reached the inner metal-rich region of ejecta. Doppler widths of the atomic lines from Si, S, and Fe correspond to velocities of 1,500–1,700 km s⁻¹, where the thermal broadening effects in this non-metal-rich plasma are negligible. Therefore, the line broadening seen in Resolve spectra is determined by the large bulk motion of ejecta. For reference, we determined a 90% upper limit on non-thermal emission from a pulsar wind nebula at 4.3 × 10⁻¹³ erg cm⁻² s⁻¹ in the 2 – 10 keV range, aligning with NuSTAR findings by Greco et al. (2022). Additionally, we searched for the ⁴⁴Sc K line feature and found a 1σ upper limit of 1.0 × 10⁻⁶ photons cm⁻² s⁻¹, which translates to an initial ⁴⁴Ti mass of approximately 2 × 10⁻⁴M⊙, consistent with previous X-ray to soft gamma-ray observations (Boggs et al. 2015; Grebenev et al. 2012; Leising 2006).