Limits to the Cas A ${}^{44}$Ti 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 \emph{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 ${}^{44}$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 \emph{BeppoSAX} detection and with the \emph{CGRO}/COMPTEL detection of the companion transition line flux for ${}^{44}$Sc decay. The mean \emph{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 $\ge$25 M${}_{\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.

12 pages, 3 tables, 1 figure, accepted for publication in the Astrophysical Journal

References in corpus (4)

• Detection of the 67.9 keV and 78.4 keV lines associated with the radioactive decay of Ti-44 in Cassiopeia A
• Accelerated Electrons in Cassiopeia A: Thermal and Electromagnetic Effects
• The X-ray Source at the Center of the Cassiopeia A Supernova Remnant
• Is the Compact Source at the Center of Cas A Pulsed?

Cited by in corpus (13)

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• On the Determination of Ejecta Structure and Explosion Asymmetry from the X-ray Knots of Cassiopeia A
• The distribution of radioactive ${}^{44}$Ti in Cassiopeia A
• The signature of 44Ti in Cassiopeia A revealed by IBIS/ISGRI on INTEGRAL
• Characterizing the non-thermal emission of Cas A
• Are Ti44-Producing Supernovae Exceptional?
• Infrared Echoes near the Supernova Remnant Cassiopeia A
• The First Measurement of Cassiopeia A's Forward Shock Expansion Rate
• Locating the most energetic electrons in Cassiopeia A
• Near-Infrared and Optical Limits for the Central X-ray Point Source in the Cassiopeia A Supernova Remnant
• Disentangling jet and disc emission from the 2005 outburst of XTE J1118+480
• Low-energy ${}^{23}$Al $\beta$-delayed proton decay and ${}^{22}$Na destruction in novae