Limits to the Cas A 44Ti Line Flux and Constraints on the Ejecta Energy and the Compact Source
Abstract
Two long observations of Cas A supernova remnant were made by the Rossi X-ray Timing Explorer in 1996 and 1997 to search for hard X-ray line emission at 67.9 and 78.4 keV from decay of 44Ti formed during the supernova event. Continuum flux was detected up to 100 keV, but the 44Ti lines were not detected. The 90% confidence upper limit to the line flux is 3.6×10-5 photons cm-2s-1. This is consistent with the recent BeppoSAX detection and with the CGRO/COMPTEL detection of the companion transition line flux for 44Sc decay. The mean BeppoSAX--COMPTEL flux indicates that 1.50.3 ×10-4M of 44Ti was produced in the supernova explosion. Based upon recent theoretical calculations, and optical observations suggesting a WN Wolf-Rayet progenitor with an initial mass of ≥25 M, the observed 44Ti yield implies that the Cas A supernova ejecta energy was 2×1051 ergs, and as a result a neutron star was formed, rather than a black hole. We suggest Cas A is possibly in the early stages of the AXP/SGR scenario in which the push-back disk has yet to form, and when the disk does form, the accretion will increase the luminosity to that of present-day AXP/SGRs and pulsed emission will commence.
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