# Light curves¶

For light-curves, we recommend to store the information in an as similar format as possible to the one for Spectra and specifically SED.

For measurements at a given time, a TIME column should be added, for measurements for a given time interval, TIME_MIN and TIME_MAX columns should be added.

As explained in Time, times should be given as 64-bit floats, using the FITS time standard to specify a reference time point. Note that this allows some flexibility, and e.g. the commonly used “MJD values” for light curves are supported via these header keys:

MJDREFI =  0
MJDREFF =  0
TIMEUNIT= 'd'


Light curve producers are highly encouraged to always give the TIMESYS. For archival data this is often not given, and it’s unclear if the times are e.g. in the UTC or TT or some other TIMESYS.

This is a very preliminary description, based on the discussion here: https://github.com/open-gamma-ray-astro/gamma-astro-data-formats/pull/61

If someone has time to provide a more detailed description, and to produce example files in FITS or possibly also ECSV format, this would be highly welcome.