Binning the data

What you will learn

You will learn how to bin COMPTEL data for an analysis with ctools.

Data need to be binned for the analysis with ctools. The data are binned in three-dimensional data cubes, called DRI (Data Required for Imaging). DRI datasets are spanned by the scatter directions \(\chi\) and \(\psi\) and the Compton scatter angle \(\bar{\varphi}\). Binned data products for an observation include event data (DRE), geometry factors (DRG) and a background model (DRB). In addition, a two-dimensional exposure map (DRX) is needed. Finally, the binned data products also include the Instrument Response Function in the so-called IAQ format, which is a two-dimensional map that provides the interaction probabilities as function of \(\varphi_{\rm geo}\) and \(\bar{\varphi}\)

You bin the data with the comobsbin tool. Binned data products will be written in a so-called data store so that they can be reused in different analyses. comobsbin will only create binned data files that do not yet exist in the datastore. The example below shows how you create binned data products for viewing period 0001.

$ comobsbin
Input observation definition file [obs.xml]
Response type (MODEL|SIM2|SIM3) [MODEL]
Algorithm for defining energy bins (FILE|LIN|LOG) [FILE] LOG
Minimum energy (MeV) (0.05-50.0) [0.75]
Maximum energy (MeV) (0.05-50.0) [30.0]
Number of energy bins (1-20) [1] 4
Phase expression in the format phasemin0-phasemax0;phasemin1-phasemax1;... [NONE]
Coordinate system (CEL - celestial, GAL - galactic) (CEL|GAL) [CEL]
Projection method (AIT|AZP|CAR|GLS|MOL|SFL|SIN|STG|TAN) [TAN]
Output folder for files [$COMDATASTORE] binned
Output observation definition file [obs_binned.xml]

Warning

Note that the creation of binned data products is relatively time consuming, in particular for geometry (DRG) and exposure files (DRX). comobsbin may typically take between 30 min and 2 hours to process the data for one viewing period, depending on the operating system and processor speed.

comobsbin produces on output an observation definition file which in the example is named obs_binned.xml. The content of this file is shown below. According to the user parameter, the energy interval 0.75-30 MeV was split into four logarithmically spaced energy bins, and a model Instrument Response Function was computed for each of the energy bins. comobsbin also generates a Phibar-normalised geometry function as a first order approximation of the instrumental background model.

<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<observation_list title="observation list">
  <observation name="CRAB" id="vp0001_0_000750-001886keV" instrument="COM">
    <parameter name="DRE" file="binned/vp0001_0_cel_dre_000750-001886keV.fits" />
    <parameter name="DRB" file="binned/vp0001_0_cel_drb_000750-001886keV.fits" />
    <parameter name="DRG" file="binned/vp0001_0_cel_drg.fits" />
    <parameter name="DRX" file="binned/vp0001_0_drx.fits" />
    <parameter name="IAQ" value="binned/iaq_000750-001886keV.fits" />
  </observation>
  <observation name="CRAB" id="vp0001_0_001886-004743keV" instrument="COM">
    <parameter name="DRE" file="binned/vp0001_0_cel_dre_001886-004743keV.fits" />
    <parameter name="DRB" file="binned/vp0001_0_cel_drb_001886-004743keV.fits" />
    <parameter name="DRG" file="binned/vp0001_0_cel_drg.fits" />
    <parameter name="DRX" file="binned/vp0001_0_drx.fits" />
    <parameter name="IAQ" value="binned/iaq_001886-004743keV.fits" />
  </observation>
  <observation name="CRAB" id="vp0001_0_004743-011929keV" instrument="COM">
    <parameter name="DRE" file="binned/vp0001_0_cel_dre_004743-011929keV.fits" />
    <parameter name="DRB" file="binned/vp0001_0_cel_drb_004743-011929keV.fits" />
    <parameter name="DRG" file="binned/vp0001_0_cel_drg.fits" />
    <parameter name="DRX" file="binned/vp0001_0_drx.fits" />
    <parameter name="IAQ" value="binned/iaq_004743-011929keV.fits" />
  </observation>
  <observation name="CRAB" id="vp0001_0_011929-029999keV" instrument="COM">
    <parameter name="DRE" file="binned/vp0001_0_cel_dre_011929-029999keV.fits" />
    <parameter name="DRB" file="binned/vp0001_0_cel_drb_011929-029999keV.fits" />
    <parameter name="DRG" file="binned/vp0001_0_cel_drg.fits" />
    <parameter name="DRX" file="binned/vp0001_0_drx.fits" />
    <parameter name="IAQ" value="binned/iaq_011929-029999keV.fits" />
  </observation>
</observation_list>