Spectral Analysis

Spectral analysis provides us with information about the energy and timing associated with the X-ray photons that Chandra detects. Learning about the energy characteristics of x-ray emission can tell us much about the material composition of the object, as well as the physical processes that it is undergoing.

The first step in spectral analysis is to extract the energy information in the form of a spectrum.

A spectrum is a one dimensional histogram of the number of x-ray photons falling into each of the discrete energy ranges (or bins) that the Chandra detector (ACIS) can identify.

Use the circular region again to

• Set up a circular region  near Physical X,Y (4050,4100). (Note: the exact position is not crucial, but try to get near this area). This will put a region near the bottom left part of the remnant. From the Analysis menu, do an energy spectrum from .1-10 KeV. This is spectrum (a).
• Do the same for a circular region near (4530,4176) near the bottom right of the remnant. This is spectrum (b).

Below is an example using a circular region near Physical X,Y (4358, 4425).

How are these plots different?  (Look specifically at where the major peaks are located on the plots).

By now, you are probably saying, "Okay, so what?  What does this all mean?"   Well first, remember, that different types of atoms gives off a unique set of colors. The colored lines, called spectral lines are a kind of "signature" for the atoms.  For more information, click on the picture below.

Team Carbon

The absorption and emission lines occur at certain wavelengths.  The wavelengths are related to the frequency of the photons, and the frequency of the photons is related to the energy of the photons.  Therefore, elements will have specific energies depending on the frequency of the photons.

Using the major spike from the spectral analysis, you can determine the elements that make up the area in the circular region you viewed.  From the spectral analysis above, we see that this section is composed of silicon.

Determine the elements that make up the regions plotted in spectrums a and b.
Spectrum A:

Spectrum B:

It may not seem that amazing, but think about what you just did.  You just used an image to determine the materials that make up an object that is 10,000 light years away!