Using Muon Rings for the Calibration of the Cherenkov Telescope Array: A Systematic Review of the Method and Its Potential Accuracy

Abstract

The analysis of ring images produced by muons in an Imaging Atmospheric Cherenkov Telescope (IACT) provides a powerful and precise method to calibrate the IACT optical throughput and monitor its optical point-spread function (PSF). First proposed by the Whipple collaboration in the early 90's, this method has been refined by the so-called second generation of IACT experiments: H.E.S.S., MAGIC and VERITAS. We review here the progress made with these instruments and investigate the applicability of the method as the primary throughput calibration method for the different telescope types forming the future Cherenkov Telescope Array (CTA). We find several additional systematic effects not yet taken into account by previous authors and propose several new analytical methods to include these in the analysis. Slight modifications in hardware and analysis need to be made to ensure that such a calibration works as accurately as required for the CTA. We derive analytic estimates for the expected muon data rates for optical throughput calibration, camera pixel flat-fielding and monitoring of the optical PSF. The achievable statistical and systematic uncertainties of the method are also assessed.

Muon calibration of the ASTRI-Horn telescope: preliminary results

“…and 12 p.e., and the removal of the outliers with iterative process. To each cleaned image, the standard analysis [2] was applied to reconstruct the geometrical ring parameters (centre, radius and width). The position of the muon impact point, necessary to evaluate the number of photons hitting the primary mirror, was computed using the light distribution along the rings.…”

“…The distribution of the best fit values of the PSF measured with muon reconstruction is plotted in Fig 2. Light distribution along the ring: the calibration with muons is strongly dependent on the precision on the muon impact point of the primary mirror obtained by fitting the light distribution along the ring. From the muon impact, in fact, it is possible to evaluate the number of photons hitting the telescope [2]. In our analysis both mirrors are assumed with circular shapes, that allowed us to use theoretical formulas; the secondary mirror shadow was computed taking into account the angle with the telescope axis of the incident direction of the muons [2].…”

“…From the muon impact, in fact, it is possible to evaluate the number of photons hitting the telescope [2]. In our analysis both mirrors are assumed with circular shapes, that allowed us to use theoretical formulas; the secondary mirror shadow was computed taking into account the angle with the telescope axis of the incident direction of the muons [2]. For each event, the intensity profile along the ring was accumulated in 15 bins and, after a smoothing, fitted with the theoretical profile.…”

“…Muon calibration is widely used in telescopes with large collecting areas (primary mirror diameter >10m) [2], but in the case of a small size telescope (diameter ∼4m) this method presents several challenging aspects. A first application of muon calibration on small size telescope has been obtained with FACT [3], and evaluations based on simulated data for ASTRI-Horn [4] were presented in [5].…”

The Application of Electromagnetic Sensors for Determination of Cherenkov Cone Inside and in the Vicinity of the Detector Volume in Any Environment Known

“…If one or more electromagnetic sensors, do not transmit the data received at the collection point for various reasons (very low energetic level detection by the electromagnetic sensors, significant errors, etc. ), then the determination of the Cherenkov cone will be erroneous [ 14 ].…”