Last modified: 24 October 2023


Choosing an Energy Filter


In many cases, the threads recommend that you filter ACIS event files on energy before beginning the analysis. See the Filtering Data and Analysing the ACIS Background with the "Blank-Sky" Files threads for examples. Be aware that the energy column in the event file only represents the nominal energy of the incoming photon. This is fine for global energy filtering, as shown here, but any more detailed analysis involves the use of an RMF; see the CIAO Threads for more information.

Determining the Filter

There are several things to consider when choosing an energy filter for your data. Four major concerns are outlined below with sample filters for illustrative purposes. Depending on your analysis needs, it may be necessary to combine several of the following examples into one energy filter.