9.1. Powerlaw

Before doing this exercise, we advise you to read How to run SPEX.

The spectrum in the files powerl.spo and powerl.res was recorded from a source at 6 kpc distance.

1. Load the spectrum into SPEX and plot it.

2. The calibration of the instrument is not very accurate for energies below 0.3 keV and above 10 keV. Ignore those parts of the spectrum.

3. How many data bins do you have in the spectrum? Now try to apply optimal binning to the spectrum. How many bins are left?

4. Set up an absorbed powerlaw model. Do not forget to set the distance to the source.

5. Next step: fit the spectrum. Is it a good fit?

6. Calculate the errors on all free parameters and save your results in a text file.

7. It may be wise to save the commands that you entered in SPEX to a command file, so you can repeat the analysis where needed. Try to make such a command file.

Learning goals:

After having done this spectrum, you should know:

• How to read a spectrum in SPEX (using Data: read response file and spectrum).

• How to use the basic plot functionalities (using Plot: Plotting data and models).

• How to ignore parts of the spectrum (using Ignore: ignoring part of the spectrum).

• How to rebin a spectrum (using Bin: rebin the spectrum).

• How to set-up a simple spectral model (using Comp: create, delete and relate spectral components).

• How to set the distance (using Distance: set the source distance).

• How to do spectral fitting (using Fit: spectral fitting).

• How to determine errors on parameters (using Error: Calculate the errors of the fitted parameters).

• How to save your commands & results (using Log: Making and using command files).