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(Luigi Foschini 4 Jan 2006): I think that the keyword MJDREF is important, otherwise the time system has no reference. Indeed, the start date can be selected to be also the launch date or any other useful date. I suggested Jan 1, 2001 just to say a number, but there are no constrains on this.
(Seth Digel, 5 Jan 2006) My intent in specifying TIMEUNIT = 'days', TIMESYS = 'MJD', and omitting MJDREF was so that the time-related columns (like times of peak fluxes) would be specified in the table as absolute dates in MJD, so no reference time is needed. I guess that this might be equivalent to setting MJDREF = 0. Also, I see that according to HEASARC recommendations I should have written the unit for days as 'd'.
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Additional issues (starting 31 Dec 2005)
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