Code Architecture

Framework Structure

PINT has four basic classes: TOAs Class, Timing Model Class, Residual Class, and Fitter Class. The connection is showed in the figure below.

Treatment of Times

Raw TOA times are assumed to be UTC as measured by an observatory clock, however they are represented as astropy.Time objects, so it should be OK to specify them in different time systems (TAI, TT, TDB).

Time corrections are then applied to obtain some realization of UTC (is this supposed to be UTC(NIST), UTC(GPS), or what??) in this sense:

UTC = UTC(obs) + CLOCK_CORRECTION

From there, TDB is computed from UTC using the time conversions built in to the astropy.Time class, which proceeds via the following flowchart:

Classes for TOAs

Individual arrival times are represented by a TOA object, while a collection of them are represented by the TOAs object. TOA objects are generally only transitory, since most of the useful functionality for computing with TOAs is implements in the collective TOAs class

TOA Class

The TOA class represents a single time of arrival. It has the following instance variables

• mjd This is an astropy.time object representing the arrival time. It is generally the UTC time recorded by an observatory clock, but can be in a different time system in certain cases (such as barycentric arrival times).
• obs This is one of the observatory codes specified in $PINT/datafiles/observatories.txt. These represent a location in ITRF coordinates and assume an observatory fixed to the rotation Earth.
• error This is the uncertainty in the mjd as an astropy Quantity with units (typically microseconds)
• freq This is the observatory-centric frequency of the observed TOA as an astropy Quantity with units (typically in MHz)
• flags This is any number of keyword=value pairs that provided additional metadata for the TOA (e.g. backend=GUPPI, ...)
• (SUGGESTION TOAs should be able to have a position and velocity specified per TOA instead of an observatory. Perhaps this can be implemented as a special obs code.)

TOAs Class

This class represents a collection of TOAs. Rather than do this as a collection of TOA objects, the information is kept in an astropy.Table for computational efficiency. A TOAs object can be instantiated from TEMPO/Tempo2 'tim' files or from a previously pickled TOAs object. (Soon it will also be able to be instantiated from a list of TOA objects, but this is not in the master branch yet)

The instance variables include:

• toas a list of TOA objects. This only exists until the table is created.

PINT model classes

##Introduction PINT model classes are a set of classes which provide the timing model calculation,majorly time delays,phases and delay derivatives. It is an independent module from TOA class module. All the model classes are subclasses of TimingModel class.

##Get your model The easiest way to get your model is using PINT built in models. If you have a .par file, a type of file provides a set of model parameters. To build your model, just simply do:

>>>import pint.models.model_builder as mb
>>>mb.get_model('filename.par')