gtpspec Help File

Searches for pulsations in wide frequency range using the Discrete Fast Fourier Transfer (FFT) technique.

Usage: evfile scfile psrdbfile psrname outfile binwidth numbins timeorigin usertime userformat usersys ra dec ephstyle f1f0ratio f2f0ratio p1p0ratio p2p0ratio

gtpspec searches for pulsations in a relatively wide range of frequencies. It uses the Discrete Fast Fourier Transfer (FFT) technique to compute power spectrum density. This tool is suitable for a so-called blind period search, in which data are examined for pulsations at any frequency. Ephemeris information can be given in one of the following forms:

• Manually input the source (pulsar) location (for the barycentric correction), pulse
  frequency or period, and related information.

• Automatically extracted from a pulsar ephemerides database, available online. If necessary, this tool reads the spacecraft orbit file and performs the barycentric correction, the p-dot cancellation, and the binary demodulation to each photon arrival time on-the-fly.

Example: gtpspec

The example below shows how to perform a pulsation search in the simplest case, where one can assume no significant frequency variations exist throughout the observation. The time origin of
this search is taken to be the center of the observation. That means, if a pulsation is found, the pulse frequency should be interpreted as measured at the center of the observation (i.e.,
the time origin).

>	gtpspec evfile=fakepulsar_event.fits \ scfile=simscdata_1week.fits \ psrdbfile=bogus_pulsardb.fits psrname="PSR J9999+9999" \ outfile=gtpspec_example_1.fits binwidth=0.01 numbins=1000000 \ timeorigin=MIDDLE ra=111.11 dec=22.22 ephstyle=FREQ \ f1f0ratio=0.0 f2f0ratio=0.0

This command produces an output message that describes the search criteria and explains the search result. A plot will also be produced.

Pulser Ephemeris Database File

A pulsar ephemeris database file is a FITS file or a text file in a Fermi-specific format, and contains a set of pulsar ephemerides to be used in a temporal analysis of Fermi data. When so specified, the pulsar analysis Science Tools load pulsar ephemerides from pulsar ephemeris database files, and use them in their tasks. A pulsar ephemeris database file can be created, filtered, and combined by the gtpulsardb tool.

Pulsar ephemerides for the Fermi LAT pulsars and timing models associated with various Fermi publications are also available on the FSSC's Gamma-ray Pulsar Timing Database page.