LIMITS TO THE CASSIOPEIA A ~(44)Ti LINE FLUX AND CONSTRAINTS ON THE EJECTA ENERGY AND THE COMPACT SOURCE

摘要

Two long observations of the 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 x 10~(-5) photons cm~(-2) s~(-1). This is consistent with the recent BeppoSAX detection and with the Compton Gamma Ray Observatory /Imaging Compton Telescope (CGRO/COMPTEL) detection of the companion transition line flux for ~(44)Sc decay. The mean BeppoSAX-COMPTEL flux indicates that 1.5 +- 0.3 x 10~(-4) solar mass of ~(44)Ti was produced in the supernova explosion. On the basis of recent theoretical calculations and optical observations suggesting a WN Wolf-Rayet progenitor with an initial mass of ≥25 solar mass, the observed ~(44)Ti yield implies that the Cas A supernova ejecta energy was ～2 x 10~(51) ergs, and as a result a neutron star was formed, rather than a black hole. We suggest that Cas A is possibly in the early stages of the anomalous X-ray pulsar/soft gamma-ray repeater (AXP/SGR) scenario in which the pushback 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.