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 are ${}^{56}$Ni, with its decay products ${}^{56}$Co and ${}^{56}$Fe, and ${}^{44}$Ti, which are studied through their X-rays 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 tension exists in determining the initial mass of ${}^{44}$Ti. Previous analysis, relying on \textit{NuSTAR} and \textit{INTEGRAL} data, report $M_{44}=(1.5\pm 0.3)\times 10^{-4}$ $M_{\odot }$ and $M_{44}=(3.1\pm 0.8)\times 10^{-4}{M}_{\odot }$, respectively. In this paper we estimate the initial mass of ${}^{44}$Ti via its decay product, the ${}^{44}$Sc emission line at 4.09 keV, using \textit{Chandra} observations. Methods. We perform 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 provide the detection of ${}^{44}$Sc emission line in the central part of SN 1987A with a $\sim$99.7\% (3 $\sigma$) significance. Results. The simultaneous fit of the spectra extracted from observations between 2016 and 2021 provides a line flux of $6.8_{-2.3}^{+2.2}\times 10^{-7}$ photons s${}^{-1}$ cm${}^{-2}$ corresponding to a ${}^{44}$Ti mass $M_{44}=(1.6\pm 0.5)\times 10^{-4}{M}_{\odot }$ (errors at the $90\%$ confidence level). The results obtained with our spectral analysis seem to align with those derived with NuSTAR.

Accepted in A&A, 6 pages, 4 figures, 5 pages Appendix

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