NAME

    gtexposure - Compute exposure for a light curve

USAGE

    gtexposure infile scfile irfs srcmdl target specin ra dec rad
    apcorr emin emax enumbins

DESCRIPTION

    Given a counts light curve prepared using gtbin for a specific
    location on the sky, this tool computes the exposure (cm2-s)
    associated with each time bin,allowing for a light curve in photons/s
    to be computed.

    If the light curve file contains DSS keywords from gtselect that
    describe an acceptance cone on the sky from which the events are
    extracted, then this tool will perform an aperture correction, i.e.,
    it will adjust the exposure as a function of energy to account for the
    tails of the psf that lie outside the acceptance cone.

    In order to provide reasonably accurate flux estimates for broad
    energy bands, the exposure must be weighted by a function that
    approximates the spectral shape of the target source. This function
    may either be specified using an XML model definition such as those
    used with gtlike, or it may be given as a simple spectral index.

PARAMETERS

    infile [file]
    Input count-space light curve file produced using gtbin.

    scfile [file]
    spacecraft pointing history file, obtained from the FSSC LAT data server.

    irfs [string]
    Reference to the LAT Instrument response functions e.g. P6_V3_DIFFUSE.

    srcmdl = none [string]
    XML file containing the Likelihood model for the target source.

    target [string]
    The name of the target source in the XML model file.

    specin = -2.1 [double]
    Photon spectral index to use for weighting the exposure as a function
    of energy. If srcmdl=none and target="", then this is used in lieu of
    the full Likelihood model.

    (ra = 0) [double]
    Right Ascension (degrees J2000) of the source (or extraction
    region). This is used only if infile lacks DSS keywords describing the
    acceptance cone.

    (dec = 0) [double]
    Declination (degrees J2000) of the source (or extraction region). This
    is used only if infile lacks DSS keywords describing the acceptance
    cone.

    (rad = 180) [double]
    Radius (degrees) of the extraction region. This will be used for the
    aperture correction.

    (apcorr = yes)
    Flag to apply aperture-correction. Users may wish to disable this to
    determine the full exposure as a function of time at a given location.

    (emin = 100)
    Minimum energy (MeV) over which to integrate the exposure. This is
    used only if infile lacks DSS keywords describing the energy range of
    the events.

    (emax = 2e5)
    Maximum energy (MeV) over which to integrate the exposure. This is
    used only if infile lacks DSS keywords describing the energy range of
    the events.

    (enumbins = 30)
    Number of energies, logrithmically-spaced, at which to evaluate the
    exposure for the weighted integral. 30 over 4.5 decades in energy
    should be sufficient for most spectral shapes.
    
    (chatter = 2) [integer]
         This parameter fixes the output verbosity: no screen output (0),
         nominal screen output (2), maximum verbosity (4). Default is "2".

    (clobber = yes) [boolean]
         If true, an existing file of the same name will be overwritten.
         Default is "yes".

    (debug = no) [boolean]
         Activate debugging mode. Default is "no". 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 is activated if set to "yes".
         Default is "no".

    (mode = ql) [string]
         Mode of automatic parameters: "h" for batch, "ql" for interactive.
         Default is "ql".