Overabundance of Calcium in the Young SNR RX J0852–4622: Evidence of Over-Production of 44Ti

Recently, COMPTEL has detected γ-rays of 1157 keV from 44Ti in the direction of the SNR RX J0852–4622 (Iyudin et al. 1998, AAA 70.125.077). Since 44Ti is a product of explosive nucleosynthesis and its half lifetime, τ1/2, is about 60 yr, RX J0852–4622 must be a young supernova remnant and radiation is dominated by the ejecta rather than by interstellar matter. We have detected an X-ray emission line at 4.1 ± 0.2 keV which is thought to come from highly ionized Ca. The emission line is so far only seen in the north-west shell region of RX J0852–4622. The X-ray spectrum can be well fitted with that of a thin hot plasma of cosmic abundances, except that of Ca, which is overabundant by a factor of 8 ± 5. Assuming that most of the Ca is 44Ca, which originates from 44Ti by radioactive decay, we estimate a total Ca mass of about 1.1 × 10−3M⊙. Combining the amount of 44Ca and the observed flux of the 44Ti γ-ray line, the age of RX J0852–4622 is around 1000 yr.