Serguei Vorobiov - Profile on Academia.edu (original) (raw)

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Papers by Serguei Vorobiov

Research paper thumbnail of Performance of Silicon Photomultipliers for the Dual-Mirror Medium-Sized Telescopes of the Cherenkov Telescope Array

Proceedings of The 34th International Cosmic Ray Conference — PoS(ICRC2015), 2016

Research paper thumbnail of Performance of the SST-1M telescope of the Cherenkov Telescope Array observatory

Proceedings of The 34th International Cosmic Ray Conference — PoS(ICRC2015), Aug 18, 2016

Research paper thumbnail of Performance of a small size telescope (SST-1M) camera for gamma-ray astronomy with the Cherenkov Telescope Array

Proceedings of 35th International Cosmic Ray Conference — PoS(ICRC2017), 2017

for the CTA SST-1M Project.

Research paper thumbnail of Auger average scaler rate variability in 2015

Auger average scaler rate variability in 2015

Research paper thumbnail of Hess J1731-347

Research paper thumbnail of Air-Shower Reconstruction at the Pierre Auger Observatory based on Deep Learning

Proceedings of 36th International Cosmic Ray Conference — PoS(ICRC2019), 2019

The surface detector array of the Pierre Auger Observatory measures the footprint of air showers ... more The surface detector array of the Pierre Auger Observatory measures the footprint of air showers induced by ultra-high energy cosmic rays. The reconstruction of event-by-event information sensitive to the cosmic-ray mass, is a challenging task and so far mainly based on fluorescence detector observations with their duty cycle of approx15\approx 15 \%approx15. Recently, great progress has been made in multiple fields of machine learning using deep neural networks and associated techniques. Applying these new techniques to air-shower physics opens up possibilities for improved reconstruction, including an estimation of the cosmic-ray composition. In this contribution, we show that deep convolutional neural networks can be used for air-shower reconstruction, using surface-detector data. The focus of the machine-learning algorithm is to reconstruct depths of shower maximum. In contrast to traditional reconstruction methods, the algorithm learns to extract the essential information from the signal and...

Research paper thumbnail of Arrival directions of the highest-energy cosmic rays detected with the Pierre Auger Observatory

Proceedings of The 34th International Cosmic Ray Conference — PoS(ICRC2015), 2016

We present the results of a search for small to intermediate scale anisotropies in the distributi... more We present the results of a search for small to intermediate scale anisotropies in the distribution of arrival directions of ultra-high energy cosmic rays recorded at the Pierre Auger Observatory. The data set, gathered in ten years of operation, includes arrival directions with zenith angles up to 80 • , and is about three times larger than that used in earlier studies. We update the test based on correlations with active galactic nuclei (AGNs) from the Véron-Cetty and Véron catalog, which does not yield a significant indication of anisotropy with the present data set. We perform a blind search for localized excess fluxes and for self-clustering of arrival directions at angular scales up to 30 • and for different energy thresholds between 40 EeV and 80 EeV. We also examine the correlation of arrival directions with relatively nearby galaxies in the 2MRS catalog, AGNs detected by Swift-BAT,and a sample of radio galaxies with jets and with the Centaurus A galaxy. None of the searches shows a statistically significant evidence of anisotropy. The two largest departures from isotropy that were found have a post-trial probability ≈ 1.4%. One is for cosmic rays with energy above 58 EeV that arrive within 15 • of the direction toward Centaurus A. The other is for arrival directions within 18 • of Swift-BAT AGNs closer than 130 Mpc and brighter than 10 44 erg/s, with the same energy threshold.

Research paper thumbnail of The AMIGA Muon Counters of the Pierre Auger Observatory: Performance and Studies of the Lateral Distribution Function

Proceedings of The 34th International Cosmic Ray Conference — PoS(ICRC2015), Aug 18, 2016

The AMIGA enhancement (Auger Muons and Infill for the Ground Array) of the Pierre Auger Observato... more The AMIGA enhancement (Auger Muons and Infill for the Ground Array) of the Pierre Auger Observatory consists of a 23.5 km 2 infill area where air shower particles are sampled by water-Cherenkov detectors at the surface and by 30 m 2 scintillation counters buried 2.3 m underground. The Engineering Array of AMIGA, completed since February 2015, includes 37 scintillator modules (290 m 2) in a hexagonal layout. In this work, the muon counting performance of the scintillation detectors is analysed over the first 20 months of operation. Parametrisations of the detector counting resolution and the lateral trigger probability are presented. Finally, preliminary results on the observed muon lateral distribution function (LDF) are discussed.

Research paper thumbnail of Test results of a prototype device to calibrate the Large Size Telescope camera proposed for the Cherenkov Telescope Array

Proceedings of 35th International Cosmic Ray Conference — PoS(ICRC2017), 2017

Research paper thumbnail of The Instrument Response Function Format for the Cherenkov Telescope Array

Proceedings of The 34th International Cosmic Ray Conference — PoS(ICRC2015), 2016

a for the CTA Consortium †

Research paper thumbnail of Calibration of the Cherenkov Telescope Array

Proceedings of The 34th International Cosmic Ray Conference — PoS(ICRC2015), 2016

Research paper thumbnail of Performance of the Cherenkov Telescope Array

Proceedings of 35th International Cosmic Ray Conference — PoS(ICRC2017), 2017

The Cherenkov Telescope Array (CTA) is expected to become the by far largest and most sensitive o... more The Cherenkov Telescope Array (CTA) is expected to become the by far largest and most sensitive observatory for very-high-energy gamma rays in the energy range from 20 GeV to more than 300 TeV. CTA will be capable of detecting gamma rays from extremely faint sources with unprecedented precision on energy and direction. The performance of the future observatory derived from detailed Monte Carlo simulations is presented in this contribution for the two CTA sites located on the island of La Palma (Spain) and near Paranal (Chile). This includes the evaluation of CTA sensitivity over observations pointing towards different elevations and for operations at higher night-sky background light levels.

Research paper thumbnail of The flux of ultra-high energy cosmic rays after ten years of operation of the Pierre Auger Observatory

Proceedings of The 34th International Cosmic Ray Conference — PoS(ICRC2015), 2016

Research paper thumbnail of New limits on Quantum Gravity energy scale with PKS 2155-304 HESS data using a likelihood fit

Research paper thumbnail of Ultra-high energy neutrinos searches with the Pierre Auger Observatory

SciPost Physics Proceedings, 2019

In the EeV range, neutrinos are expected to be produced by ultra-high energy cosmic rays interact... more In the EeV range, neutrinos are expected to be produced by ultra-high energy cosmic rays interactions with the Cosmic Microwave Background during propagation in the Universe. We report on the search for ultra-high energy neutrinos in data collected with the Surface Detector of the Pierre Auger Observatory. The searches are most efficient in the zenith angle range from 60 degrees to 95 degrees with tau neutrinos skimming in the Earth playing a dominant role. The present non-detection of UHE neutrinos in the Pierre Auger Observatory excludes the most optimistic scenarios of neutrino production in terms of UHE cosmic rays chemical composition and cosmological evolution of the acceleration sites. We also report on the searches for neutrinos in coincidence with the recent Gravitational Wave events detected by LIGO/Virgo.

Research paper thumbnail of Testing the agreement between the Xmax distributions measured by the Pierre Auger and Telescope Array Observatories

Research paper thumbnail of Construction of a Schwarzschild-Couder telescope as a candidate for the Cherenkov Telescope Array: status of the optical system

Schwarzschild-Couder Telescope, Optical System Figure 1: Left: Ray-tracing simulation of the Schw... more Schwarzschild-Couder Telescope, Optical System Figure 1: Left: Ray-tracing simulation of the Schwarzschild-Couder telescope optical system, which includes the primary and secondary mirrors as well as their respective baffles and the focal plane. Right: CAD model of the full size prototype Schwarzschild-Couder telescope (pSCT) under construction at the Fred Lawrence Whipple Observatory in Arizona.

Research paper thumbnail of Measurement of the Cosmic Ray Flux near the Second Knee with the Pierre Auger Observatory

Proceedings of 36th International Cosmic Ray Conference — PoS(ICRC2019)

We present the first measurement of the energy spectrum of cosmic rays down to 100 PeV from the P... more We present the first measurement of the energy spectrum of cosmic rays down to 100 PeV from the Pierre Auger Observatory using the part of the surface-detector array with 750 m spacing. This analysis is made possible by a set of additional particle triggers, installed in 2013, which lowers the threshold above which the array is fully efficient by half an order of magnitude. The measurement thus covers a critical energy range around 10 17 eV where previous observations have shown a change in the spectral index, the so-called second or iron knee. The work relies on a geometrical exposure, a nearly 100% duty cycle, and an almost model-independent analysis, with the energy estimation provided by the fluorescence detector. We discuss the spectrum and the associated uncertainties and compare the results to other studies in the same energy range.

Research paper thumbnail of Progress in Monte Carlo design and optimization of the Cherenkov Telescope Array

arXiv (Cornell University), Jul 10, 2013

The Cherenkov Telescope Array (CTA) will be an instrument covering a wide energy range in veryhig... more The Cherenkov Telescope Array (CTA) will be an instrument covering a wide energy range in veryhigh-energy (VHE) gamma rays. CTA will include several types of telescopes, in order to optimize the performance over the whole energy range. Both large-scale Monte Carlo (MC) simulations of CTA super-sets (including many different possible CTA layouts as subsets) and smaller-scale simulations dedicated to individual aspects were carried out and are ongoing. We summarize results of the prior round of large-scale simulations, show where the design has now evolved beyond the conservative assumptions of the prior round and present first results from the ongoing new round of MC simulations.

Research paper thumbnail of Anisotropies of the Highest Energy Cosmic-ray Events Recorded by the Pierre Auger Observatory in 15 years of Operation

Proceedings of 36th International Cosmic Ray Conference — PoS(ICRC2019), 2019

Research paper thumbnail of Performance of Silicon Photomultipliers for the Dual-Mirror Medium-Sized Telescopes of the Cherenkov Telescope Array

Proceedings of The 34th International Cosmic Ray Conference — PoS(ICRC2015), 2016

Research paper thumbnail of Performance of the SST-1M telescope of the Cherenkov Telescope Array observatory

Proceedings of The 34th International Cosmic Ray Conference — PoS(ICRC2015), Aug 18, 2016

Research paper thumbnail of Performance of a small size telescope (SST-1M) camera for gamma-ray astronomy with the Cherenkov Telescope Array

Proceedings of 35th International Cosmic Ray Conference — PoS(ICRC2017), 2017

for the CTA SST-1M Project.

Research paper thumbnail of Auger average scaler rate variability in 2015

Auger average scaler rate variability in 2015

Research paper thumbnail of Hess J1731-347

Research paper thumbnail of Air-Shower Reconstruction at the Pierre Auger Observatory based on Deep Learning

Proceedings of 36th International Cosmic Ray Conference — PoS(ICRC2019), 2019

The surface detector array of the Pierre Auger Observatory measures the footprint of air showers ... more The surface detector array of the Pierre Auger Observatory measures the footprint of air showers induced by ultra-high energy cosmic rays. The reconstruction of event-by-event information sensitive to the cosmic-ray mass, is a challenging task and so far mainly based on fluorescence detector observations with their duty cycle of approx15\approx 15 \%approx15. Recently, great progress has been made in multiple fields of machine learning using deep neural networks and associated techniques. Applying these new techniques to air-shower physics opens up possibilities for improved reconstruction, including an estimation of the cosmic-ray composition. In this contribution, we show that deep convolutional neural networks can be used for air-shower reconstruction, using surface-detector data. The focus of the machine-learning algorithm is to reconstruct depths of shower maximum. In contrast to traditional reconstruction methods, the algorithm learns to extract the essential information from the signal and...

Research paper thumbnail of Arrival directions of the highest-energy cosmic rays detected with the Pierre Auger Observatory

Proceedings of The 34th International Cosmic Ray Conference — PoS(ICRC2015), 2016

We present the results of a search for small to intermediate scale anisotropies in the distributi... more We present the results of a search for small to intermediate scale anisotropies in the distribution of arrival directions of ultra-high energy cosmic rays recorded at the Pierre Auger Observatory. The data set, gathered in ten years of operation, includes arrival directions with zenith angles up to 80 • , and is about three times larger than that used in earlier studies. We update the test based on correlations with active galactic nuclei (AGNs) from the Véron-Cetty and Véron catalog, which does not yield a significant indication of anisotropy with the present data set. We perform a blind search for localized excess fluxes and for self-clustering of arrival directions at angular scales up to 30 • and for different energy thresholds between 40 EeV and 80 EeV. We also examine the correlation of arrival directions with relatively nearby galaxies in the 2MRS catalog, AGNs detected by Swift-BAT,and a sample of radio galaxies with jets and with the Centaurus A galaxy. None of the searches shows a statistically significant evidence of anisotropy. The two largest departures from isotropy that were found have a post-trial probability ≈ 1.4%. One is for cosmic rays with energy above 58 EeV that arrive within 15 • of the direction toward Centaurus A. The other is for arrival directions within 18 • of Swift-BAT AGNs closer than 130 Mpc and brighter than 10 44 erg/s, with the same energy threshold.

Research paper thumbnail of The AMIGA Muon Counters of the Pierre Auger Observatory: Performance and Studies of the Lateral Distribution Function

Proceedings of The 34th International Cosmic Ray Conference — PoS(ICRC2015), Aug 18, 2016

The AMIGA enhancement (Auger Muons and Infill for the Ground Array) of the Pierre Auger Observato... more The AMIGA enhancement (Auger Muons and Infill for the Ground Array) of the Pierre Auger Observatory consists of a 23.5 km 2 infill area where air shower particles are sampled by water-Cherenkov detectors at the surface and by 30 m 2 scintillation counters buried 2.3 m underground. The Engineering Array of AMIGA, completed since February 2015, includes 37 scintillator modules (290 m 2) in a hexagonal layout. In this work, the muon counting performance of the scintillation detectors is analysed over the first 20 months of operation. Parametrisations of the detector counting resolution and the lateral trigger probability are presented. Finally, preliminary results on the observed muon lateral distribution function (LDF) are discussed.

Research paper thumbnail of Test results of a prototype device to calibrate the Large Size Telescope camera proposed for the Cherenkov Telescope Array

Proceedings of 35th International Cosmic Ray Conference — PoS(ICRC2017), 2017

Research paper thumbnail of The Instrument Response Function Format for the Cherenkov Telescope Array

Proceedings of The 34th International Cosmic Ray Conference — PoS(ICRC2015), 2016

a for the CTA Consortium †

Research paper thumbnail of Calibration of the Cherenkov Telescope Array

Proceedings of The 34th International Cosmic Ray Conference — PoS(ICRC2015), 2016

Research paper thumbnail of Performance of the Cherenkov Telescope Array

Proceedings of 35th International Cosmic Ray Conference — PoS(ICRC2017), 2017

The Cherenkov Telescope Array (CTA) is expected to become the by far largest and most sensitive o... more The Cherenkov Telescope Array (CTA) is expected to become the by far largest and most sensitive observatory for very-high-energy gamma rays in the energy range from 20 GeV to more than 300 TeV. CTA will be capable of detecting gamma rays from extremely faint sources with unprecedented precision on energy and direction. The performance of the future observatory derived from detailed Monte Carlo simulations is presented in this contribution for the two CTA sites located on the island of La Palma (Spain) and near Paranal (Chile). This includes the evaluation of CTA sensitivity over observations pointing towards different elevations and for operations at higher night-sky background light levels.

Research paper thumbnail of The flux of ultra-high energy cosmic rays after ten years of operation of the Pierre Auger Observatory

Proceedings of The 34th International Cosmic Ray Conference — PoS(ICRC2015), 2016

Research paper thumbnail of New limits on Quantum Gravity energy scale with PKS 2155-304 HESS data using a likelihood fit

Research paper thumbnail of Ultra-high energy neutrinos searches with the Pierre Auger Observatory

SciPost Physics Proceedings, 2019

In the EeV range, neutrinos are expected to be produced by ultra-high energy cosmic rays interact... more In the EeV range, neutrinos are expected to be produced by ultra-high energy cosmic rays interactions with the Cosmic Microwave Background during propagation in the Universe. We report on the search for ultra-high energy neutrinos in data collected with the Surface Detector of the Pierre Auger Observatory. The searches are most efficient in the zenith angle range from 60 degrees to 95 degrees with tau neutrinos skimming in the Earth playing a dominant role. The present non-detection of UHE neutrinos in the Pierre Auger Observatory excludes the most optimistic scenarios of neutrino production in terms of UHE cosmic rays chemical composition and cosmological evolution of the acceleration sites. We also report on the searches for neutrinos in coincidence with the recent Gravitational Wave events detected by LIGO/Virgo.

Research paper thumbnail of Testing the agreement between the Xmax distributions measured by the Pierre Auger and Telescope Array Observatories

Research paper thumbnail of Construction of a Schwarzschild-Couder telescope as a candidate for the Cherenkov Telescope Array: status of the optical system

Schwarzschild-Couder Telescope, Optical System Figure 1: Left: Ray-tracing simulation of the Schw... more Schwarzschild-Couder Telescope, Optical System Figure 1: Left: Ray-tracing simulation of the Schwarzschild-Couder telescope optical system, which includes the primary and secondary mirrors as well as their respective baffles and the focal plane. Right: CAD model of the full size prototype Schwarzschild-Couder telescope (pSCT) under construction at the Fred Lawrence Whipple Observatory in Arizona.

Research paper thumbnail of Measurement of the Cosmic Ray Flux near the Second Knee with the Pierre Auger Observatory

Proceedings of 36th International Cosmic Ray Conference — PoS(ICRC2019)

We present the first measurement of the energy spectrum of cosmic rays down to 100 PeV from the P... more We present the first measurement of the energy spectrum of cosmic rays down to 100 PeV from the Pierre Auger Observatory using the part of the surface-detector array with 750 m spacing. This analysis is made possible by a set of additional particle triggers, installed in 2013, which lowers the threshold above which the array is fully efficient by half an order of magnitude. The measurement thus covers a critical energy range around 10 17 eV where previous observations have shown a change in the spectral index, the so-called second or iron knee. The work relies on a geometrical exposure, a nearly 100% duty cycle, and an almost model-independent analysis, with the energy estimation provided by the fluorescence detector. We discuss the spectrum and the associated uncertainties and compare the results to other studies in the same energy range.

Research paper thumbnail of Progress in Monte Carlo design and optimization of the Cherenkov Telescope Array

arXiv (Cornell University), Jul 10, 2013

The Cherenkov Telescope Array (CTA) will be an instrument covering a wide energy range in veryhig... more The Cherenkov Telescope Array (CTA) will be an instrument covering a wide energy range in veryhigh-energy (VHE) gamma rays. CTA will include several types of telescopes, in order to optimize the performance over the whole energy range. Both large-scale Monte Carlo (MC) simulations of CTA super-sets (including many different possible CTA layouts as subsets) and smaller-scale simulations dedicated to individual aspects were carried out and are ongoing. We summarize results of the prior round of large-scale simulations, show where the design has now evolved beyond the conservative assumptions of the prior round and present first results from the ongoing new round of MC simulations.

Research paper thumbnail of Anisotropies of the Highest Energy Cosmic-ray Events Recorded by the Pierre Auger Observatory in 15 years of Operation

Proceedings of 36th International Cosmic Ray Conference — PoS(ICRC2019), 2019