IACT data

For Imaging Air Cherenkov Telescopes (IACTs), such as CTA, H.E.S.S., MAGIC or VERITAS, ctools operates on event lists. An event list is a table where each row corresponds to a registered event and each column corresponds to a property of the event. Required properties are the event identifier, the reconstructed event direction, the reconstructed event energy and the trigger time. Event lists are provided as FITS binary tables. An example for a minimal event list is shown below.

Metadata, such as the telescope pointing direction, the live time, or any other information that may be relevant for data processing, is stored in the FITS header of the event list binary table. An example for the metadata that is included in the header of the H.E.S.S. Collaboration event lists is shown below.

Every event list needs to be accompanied by a table with so-called Good Time Intervals (GTIs) where each row corresponds to a time interval of continuous data taking, and the two columns correspond to the start and stop times of these time intervals. An example for the GTIs of the H.E.S.S. event lists comprising a single GTI is shown below.

Note that times are given in so-called Mission-Elapsed Time (MET) in seconds, and that the zero-point of the MET is specified by the MJDREFI and MJDREFF keywords as the integer and fractional part of a Modified Julian Date (MJD) in the header of the GTI. The same holds also for the trigger times in the event list.

For further information on the data format we recommend to read the Data formats for gamma-ray astronomy document.