دانلود رایگان مقاله کالیبراسیون آرایه تلسکوپ چرنکوف با الکترون اشعه کیهانی

abstract

Cosmic ray electrons represent a background for gamma-ray observations with Cherenkov telescopes, initiating air-showers which are difficult to distinguish from photon-initiated showers. This similarity, however, and the presence of cosmic ray electrons in every field observed, makes them potentially very useful for calibration purposes. Here we study the precision with which the relative energy scale and collection area/efficiency for photons can be established using electrons for a major next generation instrument such as CTA. We find that variations in collection efficiency on hour timescales can be corrected to better than 1%. Furthermore, the break in the electron spectrum at ∼ 0.9 TeV can be used to calibrate the energy scale at the 3% level on the same timescale. For observations on the order of hours, statistical errors become negligible below a few TeV and allow for an energy scale cross-check with instruments such as CALET and AMS. Cosmic ray electrons therefore provide a powerful calibration tool, either as an alternative to intensive atmospheric monitoring and modelling efforts, or for independent verification of such procedures.

5. Conclusions

Tests of electron spectral reconstruction demonstrate that a measurement of the relative normalisation and energy scaling factor of the cosmic-ray electron spectrum is possible at the 3% level with under one hour of CTA observations. Such short timescale measurements make it possible to use the electron background seen in all observation runs as a “standard candle”, allowing the systematics of the gamma-ray spectral reconstruction of CTA to be assessed over the lifetime of the instrument. This technique can be used in concert with the several absolute calibration techniques for the atmosphere, individual telescopes, and for the full array, that have been proposed for CTA [20]. Together with point spread function verification using point-like gamma-ray sources (for example blazar flares), this procedure can be used as a high level check of the “health” of the instrument over its expected 30 year operational lifetime, ensuring absolute data corrections remain consistent and spectral results are stable. This conclusion can of course be extended from CTA to any instrument with substantially improved sensitivity and field of view with respect to current IACTs.