Proposal Details - 0720030
Explosive nucleosynthesis, annihilation emission and particle acceleration in Cassiopeia A and Tycho (Martin)

Proposal Abstract

We propose to observe Cas A and Tycho in order to improve our understanding of stellar explosions and their aftermaths. To allow significant advances to be made, we require an additional 7Ms of exposure, to be split over the next years starting with 2Ms in AO-7. Cas A and Tycho are respectively the remnants of a core-collapse and type Ia SNe. Their proximity on the plane of the sky offers an opportunity to study both phenomena through the observation of the gamma-ray decay lines of 44Ti. This isotope is produced in the very depths of SNe and its nucleosynthesis is highly sensitive to the physical conditions of the explosion. As such, observational constraints from SPI and IBIS on the 44Ti yields and kinematics can be a significant contribution to the understanding of the mechanisms by which stars explode. SNe are also one of the most likely sources of the galactic positrons, through the beta-decay of some of their nucleosynthesis products. Yet, it is unclear which fraction of these positrons can escape the SN and its remnant to flow into the ISM. With a substantial exposure on Cas A and Tycho, we will be able to constrain their 511keV emission with SPI and to get a valuable information about the transport of positrons in a highly turbulent medium, which is central to a full understanding of the galactic annihilation emission observed by INTEGRAL. In addition to positrons, SNRs are also established sources of cosmic-rays. The characterisation with IBIS of the hard X-ray spectra from both Cas A and Tycho will allow a better interpretation of the non-thermal emission from these objects and make it possible to estimate the maximum energy to which electrons are accelerated and the value of the magnetic field involved. Last, the field harbours several anomalous X-ray pulsars and high-mass X-ray binaries to the study of which IBIS can strongly contribute. We therefore ask for a significant amount of INTEGRAL time to be devoted to that region in the near future.

Observation Strategy (Recommended by TAC)

Total of 1 Ms in the standard 5x5 dithering mode. In order to optimize the simultaneous observation of Tycho and Cas A, and smooth out the systematic effects due to detector inhomogeneities, the region will be observed in two locations (500 ksec each) centred on (l, b) = (118, 0) and (114, 0), respectively.

Proposal grade: A

Data Rights (Recommended by TAC)

The TAC has allocated the following specific data rights to this proposal: 44Ti decay lines at 67.9. 78.4 and 1157.0 keV, and positron/electron annihilation line (511 keV) as well as ortho-positronium continuum emission.

Exposure Map

The exposure maps are in galactic coordinates and units of ksec, and the colour scale is indicated at the bottom. The green lines provide the 100 ksec contour.