Fermi Gamma-ray Space Telescope

Appendix A. Binary Modulation and Orbital Phase

Sample Files:

To try the examples, you can download simulated data files below. The simulated data is for demonstration purposes and the simulated pulsar is slightly brighter than the Vela pulsar. For more information, see the parameters used for the simulation.

Also see:

1. Periodicity Search and Pulse Phase Assignment for Binary Pulsars

Periodicity tests by gtpsearch and pulse phase assignment by gtpphase can be performed with arrival time correction for an binary orbit. The tools (gtpsearch and gtpphase) automatically look for orbital parameters in the pulsar ephemerides database for each photon; correct the photon arrival times into times at which the photons would have arrived if they were emitted at the center of gravity of the binary system in a gravity-free environment; and apply periodicity tests on -- or assign pulse phases to -- the resultant arrival times. All those actions will be performed on-the-fly, so you will not see corrected arrival times in your event file.

Since gtpsearch and gtpphase read orbital parameters from the pulsar ephemerides database, in order to analyze a binary pulsar that is not listed in the pulsar ephemerides database, you need to add an entry (or entries) to the database, so that it will contain orbital parameters for your pulsar. In the following example, gtpulsardb appends two entries listed in a text file named my_pulsardb_bin.txt to the pulsar ephemerides database named bogus_pulsardb.fits. You also need a text file that lists those file names. You can use your favorite editor to create the text file, and give it a name (e.g., filename_list.txt).

Now run gtpulsardb as follows to create an output file named bogus_pulsardb_appended.fits.

2. Orbital phase assignment for objects in a binary system

If orbital parameters are listed in the pulsar ephemerides database, or if you can add an entry (or entries) of orbital parameters of your binary system to the database (see the previous section for how to do it), then an orbital phase for each photon in your dataset can be written into your event file. In the following example, gtophase processes the event file named fakepulsar_event_bary.fits using an pulsar ephemeris (or ephemerides) in the pulsar ephemerides database named bogus_pulsardb.fits for the pulsar named "PSR J1834-0010" with a phase offset of 0.0 (i.e., no offset in phase). Note that gtophase modifies the event file (fakepulsar_event_bary.fits) in place and that nothing will be displayed when the input file is successfully processed.

Last updated by: Masaharu Hirayama 08/24/2009