NAME

    gtephem - Computes and displays a pulsar's frequency ephemeris for
              a given pulsar and instant of time.

USAGE
    
    gtephem psrdbfile psrname reftime timeformat timesys

DESCRIPTION

    This tool searches for pulsar ephemerides in a pulsar ephemerides
    database in Fermi (formerly GLAST) D4 FITS format, computes a
    pulse frequency and its time derivatives at the given time using
    the best ephemeris available, and displays the result.  If the
    given pulsar is in a binary system and its orbital parameters are
    found fin the pulsar ephemerides database, it accounts for binary
    modulation to correct time delays due to the pulsar's orbital
    motion.

PARAMETERS

psrdbfile [file name]
    Name of pulsar ephemerides database file, in Fermi (formerly
    GLAST) D4 FITS format (See PULSAR EPHEMERIS DATABASE
    FILE). Multiple files may be combined by listing them in a text
    file, one per line, and supplying the list file name preceded by
    an @ sign. If psrdbfile is NONE (case-insensitive), no ephemeris
    is loaded from a file.

psrname = ANY [string]
    Name of the pulsar, used to select only ephemerides valid for a
    particular pulsar.

reftime = 0. [string]
    Reference time for which an ephemeris will be selected, if any is
    available in the input file. The interpretation of this number is
    determined by the timeformat and timesys parameters.

timeformat = MJD [enumerated string (MJD|FERMI|GLAST)]
    String describing the representation used for the reference time.

timesys = TDB [enumerated string (TAI|TDB|TT|UTC)]
    String describing the time system used for the reference time.

(strict = no) [bool]
    If strict is yes, only spin ephemerides whose stated range of
    validity contains the epoch will be selected. If strict is no,
    the ephemeris closest to the epoch will be selected, regardless
    of its stated range of validity.

(solareph = JPL DE405) [enumerated string (JPL DE200|JPL DE405)]
    Solar system ephemeris used to select the ephemerides. This only
    has effect when the matchsolareph parameter is either ALL or
    PSRDB.

(matchsolareph = ALL) [enumerated string (NONE|PSRDB|ALL)]
    String that controls whether to use the name of the solar system
    ephemeris given by the solareph parameter to select ephemerides
    in the pulsar database. If matchsolareph is ALL or PSRDB, the
    string given by the solareph parameter is used to select the
    ephemerides. If matchsolareph is NONE, no selection will be
    performed.

(leapsecfile = DEFAULT) [file name]
    Name of the file containing the name of the leap second table, in
    OGIP-compliant leap second table format. If leapsecfile is the
    string DEFAULT, the default leap-second file (leapsec.fits),
    which is distributed with the extFiles package, will be used.

(reportephstatus = yes) [bool]
    If reportephstatus is yes, the application will examine the input
    pulsar ephemeris database, and report findings which may affect
    the requested ephemeris computations. If reportephstatus is no,
    it will not report any ephemeris status.

(chatter = 2) [integer, min=0, max=4]
    This parameter fixes the output verbosity: no screen output (0),
    nominal screen output (2), maximum verbosity (4).

(clobber = yes) [boolean]
    Overwrite or do not overwrite existing output files.

(debug = no) [boolean]
    Activate debugging mode. When debug is "no", all exceptions that
    are not caught and handled by individual tool-specific code are
    caught by a top-level exception handler that displays information
    about the exception and then exits. When debug is "yes", such
    exceptions are not caught by the top level code. Instead the tool
    produces a segmentation violation, which is more useful for
    debugging. When debugging mode is enabled, the tool produces more
    verbose output describing any errors or exceptions that are
    encountered.

(gui = no) [boolean]
    Graphical user Interface (GUI) mode activated if "yes" is
    specified.

(mode = ql) [string]
    Mode of automatic parameters.

EXAMPLES

    To find an ephemeris for a particular pulsar at a particular time,
    gtephem can be invoked as follows.

       > gtephem psrdbfile=bogus_pulsardb.fits psrname="PSR J9999+9999" \
           reftime=54870.3 timeformat=MJD timesys=TDB

    If gtephem is invoked with chatter parameter set to 4 or larger,
    it will display spin and orbital ephemerides that is used to
    compute an extrapolated spin ephemeris at a particular moment in
    time, together with an extrapolated ephemeris at the given
    time.

        > gtephem psrdbfile=bogus_pulsardb.fits psrname="PSR J1834-0010" \
           reftime=54369.3 timeformat=MJD timesys=TDB chatter=4

PULSAR 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 tools in Fermi 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. Also,
    pulsar ephemerides for the Fermi LAT pulsars and timing models
    associated with various Fermi publications are available at the
    following web page.

    http://fermi.gsfc.nasa.gov/ssc/data/access/lat/ephems/

KNOWN BUGS

      Some differences have been noted between output on Windows and
      output on Linux. The values are not qualitatively far off, but
      it is not yet known whether the differences are significant, or
      indicate a problem in the code.

SEE ALSO

    gtpulsardb
