Hard X-ray emission lines from the decay of Ti-44 in the remnant of supernova 1987A

TL;DR

This paper reports the detection of hard X-ray emission lines from Ti-44 decay in supernova 1987A, providing direct evidence of radioactive decay powering the remnant and estimating the initial Ti-44 mass near theoretical upper limits.

Contribution

First direct detection of Ti-44 decay lines in supernova 1987A, confirming its role in powering the remnant and refining initial mass estimates.

Findings

Initial Ti-44 mass estimated at (3.1+/-0.8) x 10^{-4} M_sun

Detected Ti-44 decay lines at 67.9 and 78.4 keV

Supports theoretical predictions of Ti-44 synthesis in supernovae

Abstract

It is assumed that the radioactive decay of Ti-44 powers the infrared, optical and UV emission of supernova remnants after the complete decay of Co-56 and Co-57 (the isotopes that dominated the energy balance during the first three to four years after the explosion) until the beginning of active interaction of the ejecta with the surrounding matter. Simulations show that the initial mass of Ti-44 synthesized in core-collapse supernovae is (0.02-2.5) x 10^{-4} solar masses (M_sun). Hard X-rays and gamma-rays from the decay of this Ti-44 have been unambiguously observed from Cassiopeia A only, leading to the suggestion that the values of the initial mass of Ti-44 near the upper bound of the predictions occur only in exceptional cases. For the remnant of supernova 1987A, an upper limit to the initial mass of Ti-44 of < 10^{-3} M_sun has been obtained from direct X-ray observations, and an estimate of (1-2) x 10^{-4} M_sun has been made from infrared light curves and ultraviolet spectra by complex model-dependent computations. Here we report observations of hard X-rays from the remnant of supernova 1987A in the narrow band containing two direct-escape lines of Ti-44 at 67.9 and 78.4 keV. The measured line fluxes imply that this decay provided sufficient energy to power the remnant at late times. We estimate that the initial mass of Ti-44 was (3.1+/-0.8) x 10^{-4} M_sun, which is near the upper bound of theoretical predictions.