Education Activities To Accompany
Chandra Data Analysis Software
Cas-A
Activity 5: Radial Intensity profile
To see the actual distribution
of the material in the "snowplowed" interstellar region
surrounding Cas-A, we can look at the intensity of x-rays coming
from concentric rings of material, projected onto the sky.
1. Select an annulus for your region shape,
and center the cursor over the pulsar. Click once to create the
region, and again to select it.
2. Go to the Region-->Get info...
dialog box and enter an inner radius of "0" and an
outer radius of 360, with 10 for the number of annuli. (Note:
you MUST select the region by clicking once anywhere inside it
before you go to the "get info" dialog box).
3. Click on "generate" and
then "apply". You will notice that 10 concentric rings
appear like a bulls-eye surrounding the remnant. What we will
find out is how bright the remnant is as a function of how far
you are away from the center.
4. Under analysis, click on "radial profile".
Your result shows you that the intensity of the remnant steadily
increases from the center until about 100 arc-seconds in radius.
Thereafter, the remnant gets weaker and weaker. This is what
you might expect for a more or less hollow ball, with a dense
outer shell. In fact, the exact nature of this emission and its
morphology (or shape), is a subject of intense research currently.
By looking at profiles like these, astronomers hope to gain some
insight into the nature of the original explosion, and better
understand the mechanisms by which the shock fronts form and
travel through space.
