barytime -- perform barycenter correction on EGRET data
barytime miscdir outputdir inputfile outputfile printfile coord rastring decstring angsel consiz mincon angmin angmax emin emax zensel zenmax zenoff clobber
This routine reads EGRET event files, performs user-selected cuts on photon direction, energy and quality screening parameters, and produces an output list with a column containing the solar-system barycenter corrected photon arrival times. The output file can then be used as input to other LHEAsoft temporal anlaysis tools such as "efold", "lcurve" or "powspec" to perform detailed temoral analysis (it also retains the same basic structure as the original event file, and can be used with other EGRET software). Specifically, the corrected photon arrival times in units of Julian Days are listed in the table column labled "TIME", in the first table extension (called EGRET_SMDB) of the output file.
Note that the direction specification should be that of the source in question, not that the observatory Z-axis. For a wide field-of-view instrument such as EGRET the difference becomes signifcant. This is the reason there is not simply a bary-center corrected time column in the archive files.
The input event files are in FITS table format, and follow a naming convention: "qvp3040f.fits.gz" where the 3040 indicates CGRO Viewing Period 304.0. These data are available through the HEASARC Browse system or by direct WWW or FTP download, e.g. <ftp://cossc.gsfc.nasa.gov/compton/data/egret/high_level/phase3/pnt_3040> in the case of the aforementioned example (the CGRO observing schedules or "Timelines" for the 9 year mission are available at: <http://cossc.gsfc.nasa.gov/timeline/index.html>).
This utility is derived from the program "PULSAR" developed by the EGRET instrument team.
1. Generate a SSBC corrected photon arrival time list for the Crab pulsar, using data obtained during CGRO Viewing Period 1. Photon energies between 100 and 1000 MeV are to be included.
barytime inputfil=qvp0010f.fits emin=100 emax=1000 coord=g rastring=184.56 decstring=-5.78 angsel=fixed angmin=0.0 angmax=5.0