27-10-2012, 02:15 PM
Going to the Bottom of the Explosion that Formed Cas A
ABSTRACT
The purpose of this INTEGRAL AO 1 proposal was to observe the gamma-ray lines at 1157 keV, as well as 68 keV and
78 keV of the (44)Ti decay chain from the youngest known galactic supernova remnant Cas A. The radioactive decay of (44)Ti
in Cas A was first detected by COMPTEL in the 1157 keV line and later confirmed in the lower energy lines using BeppoSAX
data. Despite the second confirming measurement, the flux value still has a considerable error, due to a low signal over
background ratio and the poor definition of the continuum background in the range of 70 - 100 keV above the line energies.
In addition to improving this flux measurement, INTEGRAL has the unique capability, in principle, to measure the line width
of the emission. This type of measurement can further constrain supernova explosion models. Unfortunately, the INTEGRAL
instrumental background, especially in the SPI spectrometer, turned out to be significantly higher than estimated at the time
of proposal submission before launch. This, and to a smaller extent the reduced effective exposure time of about 1.5 Ms
compared to requested 2.5 Ms, has precluded us from reaching the sensitivity necessary for this measurement. Studies of the
background variability with the goal of improving background modeling are ongoing, and additional 2.5 Ms observing time
has just been approved for the next observing cycle.
ABSTRACT
The purpose of this INTEGRAL AO 1 proposal was to observe the gamma-ray lines at 1157 keV, as well as 68 keV and
78 keV of the (44)Ti decay chain from the youngest known galactic supernova remnant Cas A. The radioactive decay of (44)Ti
in Cas A was first detected by COMPTEL in the 1157 keV line and later confirmed in the lower energy lines using BeppoSAX
data. Despite the second confirming measurement, the flux value still has a considerable error, due to a low signal over
background ratio and the poor definition of the continuum background in the range of 70 - 100 keV above the line energies.
In addition to improving this flux measurement, INTEGRAL has the unique capability, in principle, to measure the line width
of the emission. This type of measurement can further constrain supernova explosion models. Unfortunately, the INTEGRAL
instrumental background, especially in the SPI spectrometer, turned out to be significantly higher than estimated at the time
of proposal submission before launch. This, and to a smaller extent the reduced effective exposure time of about 1.5 Ms
compared to requested 2.5 Ms, has precluded us from reaching the sensitivity necessary for this measurement. Studies of the
background variability with the goal of improving background modeling are ongoing, and additional 2.5 Ms observing time
has just been approved for the next observing cycle.