HESS/CTA sous-page: Data Analysis/Reconstruction of TeV Data

The group has developed and is maintaining a software pipeline allowing to reduce the raw data of TeV experiments (mainly H.E.S.S., but also CTA) in order to derive the High Level Products of gamma-ray astronomy (see next section), e.g. gamma-ray sky maps, energy spectra, light curves and phasograms. This pipeline is called HAP-Fr[1], implemented in the historical analysis chain of H.E.S.S., the H.E.S.S. Analysis Package (HAP). Its architecture relies on a custom framework developed for both the on-line and off-line analysis, SASH (Storage & analysis software at H.E.S.S.). Its implementation is made in C++, using the ROOT framework on which the raw data format is based. MySQL was chosen to design all databases.

Schematics of the main steps of the data analysis pipeline.


The reconstruction of direction of the events is using the so-called Hillas analysis[2] and the Model3D reconstruction[3], where as the energy reconstruction is based on a custom algorithm [4]. A string expertise have been developed on the discrimination of the gamma/background events. Developed for H.E.S.S.[4] and applied to CTA[5], a discrimination method using a multivariate analysis provides to the analysis chain an excellent sensitivity. This method is based on sensitive and robust discriminant variables and is using Boosted Decision Trees, implemented within the TMVA package [6].

Image below: Stereo differential sensitivity in Crab units for the stereo mode and the faint source configuration, computed at Zenith=18° and Offset= 0.5° for 50 hours of observation.



  1. B. Khelifi, et al., « HAP-Fr, a pipeline of data analysis for the H.E.S.S. II experiment », Proceedings of the ICRC 2015, The Hague, Neetherlands
  2. A. Daum, et al., Astroparticle Physics, 8 (1997), Issue 1-2, p.1 (arXiv:astro-ph/9704098)
  3. M. Lemoine-Gourmard, et al., Astroparticle Physics, 25 (2006), p.195
  4. Y. Becherini, et al., Astroparticle Physics, 34 (2011), p.858B
  5. Y. Becherini, et al., « Advanced analysis and event reconstruction for the CTA Observatory », Proceedings of the 2012 Heidelberg Symposium on High Energy Gamma-Ray Astronomy http://tmva.sourceforge.net