Search for Sc-K Line Emission from RX J0852.0$-$4622 Supernova Remnant with Suzaku

We searched for evidence of line emission around 4 keV from the northwestern rim of the supernova remnant RX J0852.0$-$4622 using Suzaku XIS data. Several papers have reported on the detection of an emission line around 4.1 keV from this region of the sky. This line would arise from $K$-band fluorescence by $^{44}$Sc, the immediate decay product of $^{44}$Ti. We performed spectral analysis for the entire portion of the NW rim of the remnant within the XIS field of view, as well as various regions corresponding to regions of published claims of line emission. We found no line emission around 4.1 keV anywhere, and are able to set a restrictive upper limit to the X-ray flux: 1.1 $\times$ 10$^{-6}$s$^{-1}$cm$^{-2}$ for the entire field. For every region, our flux upper limit falls below that of the previously claimed detection. Therefore, we conclude that, to date, no definite X-ray line feature from Sc-K emission has been detected in the NW rim of RX J0852.0$-$4622. Our negative-detection supports the recent claim that RX J0852$-$4622 is neither young (1700–4000 yr) nor nearby ($\sim$750 pc).