Title: To the bottom of the explosion forming Cas A:

Title: To the bottom of the explosion forming Cas A: Observing 44Ti and the hard X-ray emission

Proposal ID: 0120125
Subject category: Nucleosynthesis
Principal investigator: Vink
Institute: Columbia University

Abstract

The detection of nuclear decay emission at 1157 keV associated with the decay of Ti-44 from Cas A by Comptel came as a surprise, as its flux implies an initial Ti-44 mass in excess of 2E-4 solar masses, higher than supernova model predictions. Observations by other instruments, mainly aimed at the other two lines produced by the decay of T-44, at 68 keV and 78 keV, failed to detect Ti-44 emission with upper limits close or even below the Comptel detection limit. Although the detection of 1157 keV line emission by Comptel seems firm, the flux level needs clearly an independent confirmation. We propose here to observe Cas A with INTEGRAL for 2500 ks, which is sufficient to observe all three nuclear decay lines simultanuously at a 4sigma level, even if the actual flux for each line isa factor 2 below the flux observed by Comptel. reliable flux estimate will determine the initial Ti-44 mass, which will strongly constrain nucleosynthesis models of the explosion that created Cas A, an alleged type 1b supernova. This will shed new lights on the mass-cut (determining the size of the stellar remnant), explosion energy and explosion assymetries. addition, with a 2500 ks observation of Cas A SPI and IBIS will allow us to observe the shape of the hard X-ray continuum up to 100 keV. This may finally settle the issue whether the emission is due to synchrotron radiation or non-thermal bremsstrahlung. Confirmation of either mechanism will provide important information on shock acceleration processes.