Measuring the initial mass of 44Ti in SN 1987A through the 44Sc emission line

Abstract

Context. Deriving the mass and large-scale asymmetries of radioactive isotopes offers valuable insights into the complex phases of a supernova explosion. Important examples include 56Ni, with its decay products 56Co and 56Fe, and 44Ti, which are studied through their X-ray emission lines, and provide a powerful diagnostic tool to probe the explosive nucleosynthesis processes in the inner layers of the exploding star. Aims. In this framework, SN 1987A provides a privileged laboratory, being the youngest supernova remnant from which the mass of Ti has been estimated. However, some uncertainty remains in determining the initial mass of 44Ti. Previous analyses, relying on NuSTAR and INTEGRAL data, report M44 = (1.5 ± 0.3) × 10-4 M⊙ and M44 = (3.1 ± 0.8) × 10-4M⊙, respectively. In this paper, we estimate the initial mass of 44Ti via its decay product, the 44Sc emission line at 4.09 keV, using Chandra observations. Methods. We performed multi-epoch spectral analysis focusing on the inner part of the remnant, to minimize the contamination from the X-ray emission stemming from the shocked plasma. As a result, we report the detection of 44Sc emission line in the central part of SN 1987A with a ∼99.7% (3 σ) significance. Results. The simultaneous fit of the spectra extracted from observations between 2016 and 2021 yields a line flux of 6.8+2.2 -2.3 ×10-7 photons s-1 cm-2, corresponding to a 44Ti mass of M44 = (1.6 ± 0.5) × 10-4M⊙ (errors at the 90% confidence level). The results obtained with our spectral analysis appear to align with those derived with NuSTAR.