Fitting Models to the Energy Spectrum

We still need to (1) convert the Channels into keV and then (2) fit models to the energy spectrum data. To do this, you need to open your Chandra data in the xspec environment. Type xspec <Enter> to call up the xspec package.

· At the xspec prompt, type the command

filename is the name that you gave to the extracted energy spectrum.

data filename.pha <Enter>

response casa.rmf <Enter>

Note: In the future, even if the source is other than Cas A, you’ll still use this command as long as the detector that made the observation was ACIS and not HRC!!! If need be, you can check this by going back to HEASARC and looking under the detector column for the observation you originally selected.

Also, be sure that the casa.rmf file is in the same folder as filename.pha!!!

(You may have to copy it into the folder containing filename.pha)

· Set the plot device by typing

cpd /xw <Enter> (You’ve done this before)

· Next, tell xspec to plot in terms of energy (keV):

setplot energy <Enter>

· Now, plot your data with the command (which you’ve also done before)

plot data <Enter>

· Finally, the command

iplot <Enter>

will allow you to rescale the x and y axes of your energy spectrum.

Now you can proceed with the same model fitting procedure that was used for EXOSAT.