XMM-Newton observations of the supernova remnant RX J0852.0-4622/GRO J0852-4642

RX J0852.0-4622 is a supernova remnant discovered in the ROSAT all-sky survey. Spatially coincident 1.157 MeV γ-ray line emission was detected with the COMPTEL instrument on-board CGRO. The analysis combining the X-ray and γ-ray data suggests that RX J0852.0-4622 is a close-by and young supernova remnant. Follow-up observations with ASCA show that the two brightest sections of the limb have non-thermal spectra, which make an independent assessment of the age and distance using the Sedov equations for the evolution of the remnant almost impossible. We have observed three rim sections of RX J0852.0-4622 with XMM-Newton and confirm the power-law type spectra measured with ASCA. We also confirm the presence of an emission-line like feature at 4.45 ± 0.05 keV, which we suggest to be emission from Ti and Sc excited by atom/ion or ion/ion high velocity collisions. The high velocity is in agreement with the width of the 1.157 MeV γ-ray line. The X-ray line flux expected from such an interaction is consistent with the 1.157 MeV γ-ray line flux measured by COMPTEL. This consistency of the X-ray line flux and the γ-ray line flux lends further support to the existence and amounts of Ti in RX J0852.0-4622 claimed by Iyudin et al. (\cite{Iyudin98}, Nature, 396, 142) and to the suggestion that RX J0852.0-4622 is young and nearby (Aschenbach et al. \cite{Aschenbach99}, A&A, 350, 997). Iyudin et al. (\cite{Iyudin98}) quote a very large broadening of the 1.157 MeV γ- ray line which would indicate a large velocity of the emitting matter of about 15 000 km s^-1. Such high ejecta velocity for Ti is found only in explosion models of sub-Chandrasekhar type Ia supernovae (Woosley & Weaver \cite{Woosley94}, ApJ, 423, 371; Livne & Arnett \cite{Livne95}, ApJ, 452, 62). In this case no compact remnant is expected. The obvious, remaining questions are what the nature and the origin of the central compact source CXOU J085201.4-461753 are and why the absorption column density apparently associated with RX J0852.0-4622 is much greater than the typical column for the Vela SNR.