This tutorial outlines the flow of a basic pulsar analysis, using the following pulsar tools:
|Pulsar Tools||Tool Tutorials|
|gtpsearch||Period Search Tutorial|
|gtpspec||Pulsation Search Tutorial|
|gtptest||Periodicity Test Tutorial|
|gtpphase||Pulse Phase Calculation|
|gtephem||Ephemeris Computation Utility|
Download data, screen events as you do for your spectral or image analysis.
Note: For maximum pulse-detection sensitivity, select only events within a relatively small spatial region, typically one degree or less ; steady flux is a "noise" for your periodicity searches and for periodicity significance tests.
Also see: Tim Naylor's Optimal Photometry Page for optimal spatial region size for the highest signal-to-noise ratio.
Two sets of parameters are commonly used in pulsar timing analyses:
These parameters (the ephemeris information of your pulsar) may or may not be available for your analysis; if they are, it will be helpful to collect such information before going any further. You might also find ephemeris information of your pulsar in the pulsar ephemerides database. It is a FITS file containing spin and orbital parameters and other related information for your convenience and can be viewed with the FTOOL fv. If your pulsar is not listed in the database, you might want to look for ephemeris information in the literature. Parameters you need to collect for the pulsar tools include:
|t0:||an ephemeris epoch, or an arbitrary chosen origin of time|
|φ0:||pulse phase at time t0|
|f0:||pulse frequency at time t0|
|f1:||the 1st time derivative of frequency at time t0|
|f2:||the 2nd time derivative of frequency at time t0|
NOTE: f0, f1, and f2 can be replaced by p0, p1, and p2, which are pulse period at time t0, the 1st time derivative of period at time t0, the 2nd time derivative of period at time t0, respectively.
|PBDOT:||first time derivative of PB (orbital period)|
|A1:||projected semi-major axis in light seconds|
|XDOT:||first time derivative of A1 (projected semi-major axis)|
|ECCDOT:||first time derivative of ECC (eccentricity)|
|OM:||longitude of periastron|
|OMDOT:||first time derivative of periastron longitude|
|T0:||barycentric time (TDB scale) of periastron in MJD|
|GAMMA:||time-dilation and gravitational redshift parameter|
|SHAPIRO_R:||range parameter of Shapiro delay in binary system|
|SHAPIRO_S:||shape parameter of Shapiro delay in binary system|
With the ephemeris information of your pulsar, you can calculate a pulse phase for each photon and test for periodicity in your dataset.IMPORTANT: Because the LAT data are sparse, long accumulation time is required. Calculating a pulse phase therefore requires precise position and timing information for the pulsar.
The FSSC science tool gtpphase processes the event file using a pulsar ephemeris (or ephemerides) in the pulsar ephemerides database, or equivalent information entered manually. The tool modifies the event file in place and nothing will be displayed when the input file is successfully processed. For more details, see the gtpphase tutorial.
The next step is to use the FSSC science tool gtptest to test the phase folded event file for periodicity. The tool produces output from several statistical tests and a graphical plot of a folded light curve on your screen. For more details, see the gtptest tutorial.
If the entire dataset is not covered by the timing information in the pulsar ephemerides database, or if you have only an approximate timing ephemeris, you may be able to use the FSSC science tool gtpsearch to refine the pulsar ephemeris for your particular dataset. A provisional ephemeris for such an analysis may be found in the literature, or the FSSC science tool gtephem may find an ephemeris entry for your pulsar in the database. For more details, see the gtephem tutorial. The gtpsearch tool can then be run to check the precision of the ephemeris at the time of your observation and to refine the ephemeris. For more details, see the gtpsearch tutorial. If gtpsearch finds a timing ephemeris that produces a significant pulse signal, this ephemeris can be used with gtpphase to assign a pulse phase to each event.
The details on a full pulsation search are beyond the scope of this tutorial and not described here.
For more information about pulsar analysis, see the Pulsar Analysis Cicerone.
Last updated by: Masaharu Hirayama 08/20/2009