Contents of: VI/111/./abstract/RTUFFS_SNR.abs

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SCIENTIFIC ABSTRACT
We propose a spectrophotometric and spectropolarimetric investigation of the 
prototype young galactic supernova remnants Cas A and the Crab Nebula, 
respectively. This investigation addresses the possible formation, composition 
and destruction of grains in these objects, the properties of dust and gas in 
the pre-existing circum-progenitor media (CPM), and the chemical composition and
dynamics of the ejecta. We further propose to study the early stages in the 
evolution of the remnant of SN1987A, which could be a brightening infrared 
source during the lifetime of ISO. In the event of an autumn launch the Crab 
Nebula will be not visible to ISO, and we intead propose an investigation of the
shock processing of interstellar grains at the blast wave of the Cygnus Loop.

OBSERVATION SUMMARY
Using PHT-C we propose to measure several positions within the Crab Nebula in 
it's polarised synchrotron emission at 12, 25, 60 and 100 micron. This addresses
the question of the origin of the ``bump'' in the FIR spectrum detected by IRAS.
The positions for polarimetry are chosen to be at positions of different 
magnetic field orientations as revealed from maps of the radio synchrotron 
emission. Oversampled absolute photometric mapping in total power at 60, 100, 
and 200 micron will be achieved by concatenating linear scans taken in the 
absolute photometry mode to two dimensional mapping observations. This will 
establish the integrated spectrum of the nebula in the FIR, and will measure the
spatial distribution of mass column densities and temperatures of the grains in
the nebula. Spectrophotometric mapping of the entire nebula using PHT-S will 
probe the chemical composition of the grains, and provide a survey of line 
emission from more highly ionised species in the photoionised gas than can be 
seen in the UV and visible. These measurements are complemented by the ISOCAM 
mapping of the nebula by Lagage et al.

PHT-C diffraction-limited mapping of Cas A at 200, 160, 100 and 60 micron should
provide a definitive measurement of the mass of any grains present in unshocked,
cold dense regions of the metal rich ejecta, which should be mainly interior to
the hot component of emission collisionally heated by shocked gas in the shell
of the remnant. PHT-S mapping will probe the location and compositions of the 
ejecta and circumprogenitor medium, both in the gas and solid state components.
A particular aim is to investigate the possible presence of gas components with
densities and temperatures intermediate between those found in the dense fast 
optical filaments and the diffuse X-ray emitting plasma. The spectral resolution
of approximately 3000 kms**-1 should provide information on the pattern of
velocities of ejected species emitting infared fine structure line emission. 
A map with a finer raster will be made with PHT-S towards the complex of fast 
optical filaments outside the shell to the North-East. A deeper single pointing
will be made with PHT-S towards the expansion centre of the remnant. These 
observations are complementary to the ISOCAM mapping observations of Cas A 
proposed by Lagage et al.

The remnant of SN1987A will be observed with the PHT-C100 and PHT-C200 arrays in
the C60, C90, C160 and C180 filters to measure any dust from the ejecta/
circumprogenitor medium in the 10 - 30 K temperature range. To lower the 
FIR confusion limit from interstellar dust emission from the LMC, spatially 
oversampled scans will be taken through the source. Warmer dust associated with 
the blast wave/shocked gas will be searched for using the PHT-P2 detector with 
the 25 micron filter at a fixed spacecraft raster position with the focal plane
chopper in it's triangular mode. Optimum sensitivity and angular resolution for
broad-band emission from the supernova/cpm in 12-18 micron range will be 
provided by ISOCAM using it's smallest pixel size and longest readout interval.
The ISOCAM image will also be sensitive to echo emission structures from the 
interstellar medium around the supernova. The limiting rms flux densities to 
point sources reached in the 12-18/25/60/90/160/180 micron filters is predicted
to be approximately 0.01/8/3/1/3/4 mJy respectively.

Continuued in scientific justification section...


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