Editing OP313 Dec2023 Jan2024 LST1 analysis details (section)

== Systematic on the energy scale  ==


Test the effect of a +/-15% shift on a possible bias on the absolute energy scale between simulations and observed data. This is the typical value used in currents IACTs and also it was found by Federico Di Pierro et al. to be the energy scale mismatch between LST-1 and MAGIC.

This can be done at different analysis levels:

* Post DL3 in Gammapy (e.g. have a look at https://github.com/bkhelifi/CTAO-CTAC_Meeting_Granada_2023/blob/main/Crab_simulations_systematic_errors_Solution.ipynb)
[[File:SED_OP313_energy_scale_gammapy.png|900px]]

* Scaling of true energy in IRFs by ±15%

[[File:SED_OP313_energy_scale_pyirf.png|900px]]

{| class="wikitable"
|+ Best-fit spectral parameters after scaling the true energy by ±15%
|-
! Energy true scale !! Index !! Amplitude [x 10<sup>-8</sup> TeV<sup>-1</sup> s<sup>-1</sup> cm<sup>-2</sup>] 
|-
| +15% || 1.78 ± 0.55 || 1.80 ± 0.30
|-
| -15% || 2.57 ± 0.38 || 0.60 ± 0.10
|}


* DL1: scaling the pixel charges
Using rescale_dl1_charge 

Analysis changing the amount of light. Trigger and fluctuations are not affected, but all the rest, starting from cleaning are. Better to try this first before producing low-level MC.

* Simtel files (simulating new MC productions scaling the light yield, e.g. +/- 15 %): before doing this test, first try the approach at DL1 level scaling the charge.