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User's Guide: Cold Plasma EffectsWhen supported by the underlying file format, PSRCHIVE maintains and can differentiate between cold plasma effects (dispersion and birefringence) that arise in the interstellar medium from those that arise in the Earth's ionosphere or the solar system. Anything that is not interstellar is called auxiliary; however, the auxiliary dispersion measures and rotation measures can also be used to represent changes in interstellar DM / RM.
Interstellar DM and RM parametersThe interstellar dispersion measure (DM) and Faraday rotation measure (RM) and their related correction flags are stored in the primary header of a file and can be queried and set using psredit:
Auxiliary DM and RM parametersThe following six parameters are used to store information about auxiliary dispersion and birefringence and can be queried and set using psredit:
Example Usage: Edit auxiliary RM using a psrshscriptFor example set the rotation measure due to the ISM to 166 and the rotation measure due to the ionosphere to -9.9 for the first sub-integration and -8.7 for the second sub-integration, create and run the following psrsh script:#!/usr/bin/env psrsh edit rm=166 edit int[0]:aux:rm=-9.9 edit int[1]:aux:rm=-8.7 Example Usage: Add the required auxiliary RM extension using psreditIf a data file supports optional storage of auxiliary cold plasma parameters but does not yet contain the relevant extensions, they can be added with a command like the followingpsredit -c int:ext=+aux -c int:aux:rm=1.0 filename.ar -e newHere -c int:ext=+aux instructs psredit to add the relevant extensions and -c int:aux:rm=1.0 sets the auxiliary RM to 1.0 in every sub-integration. The auxiliary RM must be set to a non-zero value in at least one sub-integration. Instead of setting it to unity in every sub-integration, it is possible to set the values independently for every sub-integration, either on the command line; e.g. psredit -c int:ext=+aux -c 'int[0]:aux:rm=1.2' -c 'int[1]:aux:rm=3.4' filename.ar -e newor by providing a text file containing all of the same strings; e.g. psredit -c int:ext=+aux -C setrm.txt filename.ar -e newwhere setrm.txt contains the following lines int[0]:aux:rm=1.2 int[1]:aux:rm=3.4 Expected BehaviourWhen either an fscrunch or tscrunch is performed:
When defaraday/dedisperse is performed:
For further information about weighted centre frequencies, the meanings of the rmc and dmc flags, and the behaviour of PSRCHIVE when integrating in time and frequency, please read Weighted Means.
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