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 the decay of ^ { 44 } Ti formed during the supernova event .
Continuum flux was detected up to 100 keV , but the ^ { 44 } Ti lines were not detected .
The 90 % confidence upper limit to the line flux is 3.6 \times 10 ^ { -5 } photons cm ^ { -2 } s ^ { -1 } .
This is consistent with the recent BeppoSAX detection and with the CGRO /COMPTEL detection of the companion transition line flux for ^ { 44 } Sc decay .
The mean BeppoSAX —COMPTEL flux indicates that 1.5 \pm 0.3 \times 10 ^ { -4 } M _ { \odot } of ^ { 44 } Ti 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 \geq 25 M _ { \odot } , the observed ^ { 44 } Ti yield implies that the Cas A supernova ejecta energy was \sim 2 \times 10 ^ { 51 } 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 .