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PSRCHIVE user documentation: pas
1.0 PurposePulsar timing is done by comparing the phase of each observed pulse with the fiducial phase of a standard template profile. The absolute phase of the standard template is not important and it is often modified so that the pulse appears in the middle or edge of the profile for ease of analysis. However, if multiple standard template profiles are required (for example, to span multiple frequency bands when there is significant evolution of the pulse profile as a function of frequency) it is essential that they are all aligned to the same absolute reference phase.
pas was designed to edit standard template profiles in a number of useful ways. Profile objects can be rotated in single or fractional bin increments (using the Fourier shift theorem), baseline noise can be zeroed and two different profiles can be mutually aligned by maximising their cross-correlation function.
2.0 Usagepas is slightly different to most other PSRCHIVE applications in that it is an interactive GUI based on the PGPLOT subroutine library. It is invoked with the name of the Archive containing the Profile that the user wishes to edit and all other operations are controlled via the GUI. Occasionally the user is prompted to enter additional information in the terminal as well. A typical pas session begins as follows:
pas filenameThere are a number of additional command line options related to verbosity, but the most commonly used option is -r, which allows the user to specify a reference Profile as well as one to be edited. If this option is used, pas plots both profiles in the same window (though only one can actually be edited) and a number of additional processing options become available.
pas -r reference filenameBoth the reference Profile and the Profile to be edited are loaded from Pulsar::Archive objects which can be stored on disk in any of the supported file formats. Typically, the Archive containing the standard Profile will be fully scrunched in time, frequency and polarisation. If this is not the case, pas simply extracts the Profile in the first integration, polarisation and frequency channel.
3.0 Algorithmspas makes use of the various Profile::rotate methods and the same shift detection routines used to calculate arrival times. In addition, it allows the user to modify Profile amplitudes in order to zero out unwanted baseline noise.
4.0 Testing and examplesDuring a typical pas session, the first in a series of standard templates (representing widely separated frequency bands for example) is loaded and the phase of the Profile is modified so that the peak is at a convenient fiducial point. If desired, the baseline noise can be eradicated as well. Subsequent template Profiles are loaded using the -r option to specify the first one as the reference. The automatic alignment function is then used to bring each of the other templates into line with the first, creating a set of templates with the same reference phase.
5.0 Known bugs and features that require implementation