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How can I correct the calibration of my PACS spectra for a pointing off-set?
Posted by Mark Kidger, Last modified by Mark Kidger on 14 September 2018 04:22 PM

We assume here that you have watched the Herschel Science Centre short videotutorial called Starting with PACS Spectroscopy:

https://www.youtube.com/watch?v=rcY487Z9Kyg 

And the Herschel Science Centre short videotutorial Point Source Spectroscopy with PACS:

https://www.youtube.com/watch?v=nYWTccEQz_M

Or, at least, are familiar with the contents of both short videotutorials and their associated documentation. If you have/are, you may find that using the PACS Pointing Off-set Correction Script will improve the quality of you results. There is a Herschel Science Centre short videotutorial that will show you how to use it and teach you the background information that you need to make effective use of it. You can find the short videotutorial here:

https://www.youtube.com/watch?v=f861D8CoYqc

The Pointing Off-set Correction Script will improve the spectra of point sources that suffer from pointing off-sets, or pointing jitter, provided that the off-set is no greater than 10 arcseconds. The script measures the average pointing off-set and its variation with time (the jitter). The script works best for:

1. Sources with a flux of about 10Jy or more.

2. Sources that are off-set by no more than 4 arcseconds.

For these objects you will get a much improved continuum shape and will be able to detect broad features much more reliably.

In contrast, the script will not work for:
  • A source located at the edge of the central 3x3 spaxel box.
  • Un-chopped spectroscopy.
And it will be unreliable for faint sources.

You can find the Pointing Off-set Correction Script in the HIPE Scripts menu and must be run from Level 0: i.e. with raw data. It is fully described in the PACS Data Reduction Guide. It will produce two spectra from the extractCentralSpectrum task - the so-called c9 and the c129 spectra - of which, the one with the higher flux is the one to use. You will see several examples of spectra of sources with off-sets from 2-6 arcseconds that have been processed with and without the Pointing Off-set Correction Script to illustrate the differences that can be found.
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