Impact of H.E.S.S. Lidar profiles on Crab Nebula data

Devin, J.; Bregeon, J.; Vasileiadis, G.; Gallant, Y. A.

doi:10.1051/epjconf/201919701001

Cited by 12 publications

(19 citation statements)

References 6 publications

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“…Therefore, atmospheric conditions are monitored during data taking in experiments such as H.E.S.S. (Aharonian et al, 2004;Devin et al, 2019), MAGIC (Aleksić et al, 2012) and VERITAS (Weekes et al, 2002;Holder et al, 2011). Additional instruments to measure the transparency of the atmosphere are also planned to be built for CTA (Doro et al, 2013;López et al, 2013;Gaug, 2016;Iarlori et al, 2016;Valore et al, 2017).…”

Section: Introductionmentioning

confidence: 99%

An analysis method for data taken by Imaging Air Cherenkov Telescopes at very high energies under the presence of clouds

Sobczyńska

Adamczyk

Sitarek

et al. 2020

Astroparticle Physics

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The effective observation time of Imaging Air Cherenkov Telescopes (IACTs) plays an important role in the detection of γ-ray sources, especially when the expected flux is low. This time is strongly limited by the atmospheric conditions. Significant extinction of Cherenkov light caused by the presence of clouds reduces the photon detection rate and also complicates or even makes impossible proper data analysis. However, for clouds with relatively high atmospheric transmission, high energy showers can still produce enough Cherenkov photons to allow their detection by IACTs. In this paper, we study the degradation of the detection capability of an array of small-sized telescopes for different cloud transmissions. We show the expected changes of the energy bias, energy and angular resolution and the effective collection area caused by absorption layers located at 2.5 and 4.5 km above the observation level. We demonstrate simple correction methods for reconstructed energy and effective collection area. As a result, the source flux that is observed during the presence of clouds is determined with a systematic error of 20%. Finally, we show that the proposed correction method can be used for clouds at altitudes higher than 5 km a.s.l.. As a result, the analysis of data taken under certain cloudy conditions will not require additional time-consuming Monte Carlo simulations.

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Section: Introductionmentioning

confidence: 99%

An analysis method for data taken by Imaging Air Cherenkov Telescopes at very high energies under the presence of clouds

Sobczyńska

Adamczyk

Sitarek

et al. 2020

Astroparticle Physics

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“…H. Abdalla 1 , H. Abe 2 , S. Abe 2 , A. Abusleme 3 , F. Acero 4 , A. Acharyya 5 , V. Acín Portella 6 , K. Ackley 7 , R. Adam 8 , C. Adams 9 , S.S. Adhikari 10 , I. Aguado-Ruesga 11 , I. Agudo 12 , R. Aguilera 13 , A. Aguirre-Santaella 14 , F. Aharonian 15 , A. Alberdi 12 , R. Alfaro 16…”

Section: Acknowledgementsmentioning

confidence: 99%

“…An approach to atmospheric corrections for IACTs has been already studied in MAGIC [8] and H.E.S.S. [5,9] collaborations. In [8] it is shown that for layers of low and moderate optical depths a straightforward correction to the reconstructed energy is possible.…”

Section: Introductionmentioning

confidence: 99%

“…The corrected energy is simply obtained as a reconstructed (estimated) energy, , scaled with the inverse of the average optical depth. In the presence of clouds event reconstruction using simulations based on cloudless atmospheric models [5,9] yields a bias in the reconstructed energy, therefore the analysis should be performed using simulations that include proper atmospheric conditions.…”

Section: Introductionmentioning

confidence: 99%

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Performance of the Cherenkov Telescope Array in the presence of clouds

Pecimotika¹,

Adamczykc²,

Prester³

et al. 2021

Proceedings of 37th International Cosmic Ray Conference — PoS(ICRC2021)

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The Cherenkov Telescope Array (CTA) is the future ground-based observatory for gamma-ray astronomy at very high energies. The atmosphere is an integral part of every Cherenkov telescope. Different atmospheric conditions, such as clouds, can reduce the fraction of Cherenkov photons produced in air showers that reach ground-based telescopes, which may affect the performance. Decreased sensitivity of the telescopes may lead to misconstructed energies and spectra. This study presents the impact of various atmospheric conditions on CTA performance. The atmospheric transmission in a cloudy atmosphere in the wavelength range from 203 nm to 1000 nm was simulated for different cloud bases and different optical depths using the MODerate resolution atmospheric TRANsmission (MODTRAN) code. MODTRAN output files were used as inputs for generic Monte Carlo simulations. The analysis was performed using the MAGIC Analysis and Reconstruction Software (MARS) adapted for CTA. As expected, the effects of clouds are most evident at low energies, near the energy threshold. Even in the presence of dense clouds, high-energy gamma rays may still trigger the telescopes if the first interaction occurs lower in the atmosphere, below the cloud base. A method to analyze very high-energy data obtained in the presence of clouds is presented. The systematic uncertainties of the method are evaluated. These studies help to gain more precise knowledge about the CTA response to cloudy conditions and give insights on how to proceed with data obtained in such conditions. This may prove crucial for alert-based observations and time-critical studies of transient phenomena.

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“…It is caused mainly by the uncertainty in the atmospheric production and absorption of the Cherenkov photons as well as lack of a "test Email addresses: jsitarek@uni.lodz.pl (Julian Sitarek), dsobczynska@uni.lodz.pl (Dorota Sobczyńska), kadamczyk@uni.lodz.pl (Katarzyna Adamczyk), mitsza@camk.edu.pl (Michał Szanecki) beam" for IACT instruments. Despite various calibration methods (inter-telescope calibration : Hofmann, 2003, muon analysis: Vacanti et al, 1994, flux comparisons at different thresholds: Aleksić et al, 2016b, LIDAR corrections: Fruck & Gaug, 2015Devin et al, 2019) it is still at the level of ∼ 15% (see e.g. Aharonian et al, 2006;Abeysekara et al, 2015;Aleksić et al, 2016b), much larger than of satellite experiments (c.f.…”

Section: Introductionmentioning

confidence: 99%

V-shaped cherenkov images of magnetically-separated gamma-rays

Sitarek

Sobczyńska

Adamczyk

et al. 2020

Astroparticle Physics

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Cherenkov Telescope Array (CTA) is an upcoming instrument that will start a new generation of atmospheric Cherenkov telescopes. CTA is expected not only to provide an unprecedented sensitivity in the tens of GeV to hundreds of TeV range, but also to considerably improve the systematic uncertainties of the measurements. We study the images registered by Cherenkov telescopes from low energy gamma rays with its first interaction in the upper parts of the atmosphere. The images show a characteristic separation due to the deflection of the first e − e + pair in the Geomagnetic Field. We evaluate the performance of the standard stereoscopic analysis for such events. We derive also a novel method for energy estimation of V-shaped events based purely on geometrical properties of the image. We investigate the potential of combining the classical energy estimation and the novel method for independent validation of the systematic shifts in the energy scale of Cherenkov telescopes and discuss the limitations of such analysis.

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Impact of H.E.S.S. Lidar profiles on Crab Nebula data

Cited by 12 publications

References 6 publications

An analysis method for data taken by Imaging Air Cherenkov Telescopes at very high energies under the presence of clouds

An analysis method for data taken by Imaging Air Cherenkov Telescopes at very high energies under the presence of clouds

Performance of the Cherenkov Telescope Array in the presence of clouds

V-shaped cherenkov images of magnetically-separated gamma-rays

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