gtpsearch Help File

Searches for pulsations at frequencies near to a known, guessed or estimated reference frequency.

Usage: evfile scfile psrdbfile psrname outfile algorithm numphase
numharm maxharm scanstep numtrials timeorigin usertime
userformat usersys ephstyle ephepoch timeformat timesys
ra dec f0 f1 f2 p0 p1 p2

This tool searches for pulsations in data which is known or suspected to have a pulsation of a known approximate period or frequency. It is not useful for a so-called blind period search, in which data are examined for pulsations at any frequency. The tool supports several test statistics available, including Chi-squared (X2), Z- squared-n ( Z2N), H, and Rayleigh (Z2N with N == 1). 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.

Examples: gtpsearch

Performing a period search is straight forward if the object of interest is listed in a pulsar ephemerides database file. The example below shows how to perform the test under these
circumstances using the files described above. The time origin of periodicity test 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).

> gtpsearch evfile=fakepulsar_event.fits scfile=simscdata_1week.fits \
psrdbfile=bogus_pulsardb.fits psrname="PSR J9999+9999" \
outfile=gtpsearch_example_1.fits algorithm=Chi2 numphase=10 \
scanstep=0.5 numtrials=800 timeorigin=MIDDLE ephstyle=DB

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.