Fluorescence Telescopes Research Articles

First results from the Telescope Array

The Telescope Array Project is a successor to the High Resolution Flyʼs Eye (HiRes) and AGASA (Akeno Giant Air Shower Array) experiments. It is the largest ultra high energy cosmic ray experiment in the northern hemisphere. The Telescope Array observatory has been collecting data since 2008 using a hybrid of fluorescence telescopes and scintillator surface detectors. Some of the first results from the experiment are presented including the monocular spectrum from the Middle Drum fluorescence site and the spectrum from the scintillator array. These are in good agreement with the spectrum from the High Resolution Flyʼs Eye. In addition, a first pass at a composition measurement is made and indicates a predominantly light composition in the 10 19 eV region. Finally, some of the ongoing work of the group is presented including a novel technique for an end to end calibration of the telescopes involving a 40 MeV linear accelerator.

Advanced functionality for radio analysis in the Offline software framework of the Pierre Auger Observatory

The advent of the Auger Engineering Radio Array (AERA) necessitates the development of a powerful framework for the analysis of radio measurements of cosmic ray air showers. As AERA performs “radio-hybrid” measurements of air shower radio emission in coincidence with the surface particle detectors and fluorescence telescopes of the Pierre Auger Observatory, the radio analysis functionality had to be incorporated in the existing hybrid analysis solutions for fluorescence and surface detector data. This goal has been achieved in a natural way by extending the existing Auger Offline software framework with radio functionality. In this article, we lay out the design, highlights and features of the radio extension implemented in the Auger Offline framework. Its functionality has achieved a high degree of sophistication and offers advanced features such as vectorial reconstruction of the electric field, advanced signal processing algorithms, a transparent and efficient handling of FFTs, a very detailed simulation of detector effects, and the read-in of multiple data formats including data from various radio simulation codes. The source code of this radio functionality can be made available to interested parties on request.

Cosmic ray Cherenkov and fluorescence imaging: Photosensors and data acquisition systems for a new generation of focal planes

In this paper the design of a new generation of focal planes for Imaging Atmospheric Cherenkov and Fluorescence Telescopes is discussed, based on a Digital Photon Counting architecture instrumented with (SiPM) Silicon Photomultipliers. 3 × 3mm2 SiPMs were chosen to minimize the photoelectron pile-up within intervals shorter than the clock sampling time. The large number of channels requires a compact, modular design with minimal cabling and distance between the photosensors and the frontend electronics. Other design requirements are a high reliability, easy field maintenance and minimization of the total power budget. Data acquisition electronics are partitioned in on-board frontend and off-detector high-level trigger electronics. Extensive use of mixed-signal ASICs and low-power FPGAs for early data reduction were adopted. Temperature is controlled by a liquid cooling sub-system. An asynchronous data readout and filtering, where each of the trigger levels works at its own clock frequency is adopted. The off-detector data acquisition and trigger architecture is based on an asynchronous multi-gigabit switching approach implemented over standard MicroTCA boards, equipped with optical interfaces and high-capability FPGAs. The boards are connected by multi-Gbps optical links to the frontend electronics. Trigger primitives are sent asynchronously to the MicroTCA trigger boards via data links running at their own clocks, for maximum bandwidth. Data and slow-control data streams are sent over the same data lines, reducing in this way the number of cables required. Each crate can process up to 4 × 104 channels and the modularity offered allows further expansion by inter-connecting additional crates with optical fiber links.

R&D for future SiPM cameras for Fluorescence and Cherenkov Telescopes

R&D for future SiPM cameras for Fluorescence and Cherenkov Telescopes

The Balloon-the-Shower programme of the Pierre Auger Observatory

The southern part of the Pierre Auger Observatory in Argentina investigates cosmic rays with energies above about 5·1017 eV. High-energy events which have been recorded with both detector components, surface water Cherenkov tanks and fluorescence telescopes, are crucial for the energy calibration of the entire detector system. Using this method, the energy reconstruction of extensive air showers relies on a proper fluorescence light reconstruction which depends on the knowledge of atmospheric conditions like pressure, temperature and water vapour. These properties of the atmosphere vary with altitude and in time. Therefore, a dedicated monitoring programme has operated since March 2009 to measure an actual atmospheric profile with meteorological radio soundings shortly after the detection of a high-energy air shower with E0 > 2·1019 eV. We will present the technical implementation of this programme as well as a reconstruction analysis using the data obtained. The reconstructed primary energy of air showers and the position of the shower maximum are compared with those results using either monthly models for the local atmospheric conditions or global meteorological models.

The exposure of the hybrid detector of the Pierre Auger Observatory

The Pierre Auger Observatory is a detector for ultra-high energy cosmic rays. It consists of a surface array to measure secondary particles at ground level and a fluorescence detector to measure the development of air showers in the atmosphere above the array. The “hybrid” detection mode combines the information from the two subsystems. We describe the determination of the hybrid exposure for events observed by the fluorescence telescopes in coincidence with at least one water-Cherenkov detector of the surface array. A detailed knowledge of the time dependence of the detection operations is crucial for an accurate evaluation of the exposure. We discuss the relevance of monitoring data collected during operations, such as the status of the fluorescence detector, background light and atmospheric conditions, that are used in both simulation and reconstruction.

Results from the Pierre Auger Observatory

The southern part of the Pierre Auger Observatory located in Province of Mendoza, Argentina, is now completed and fully operational. Data are routinely recorded since 2004, even during the construction phase. It consists of a ground array of more than 1.600 water-Cherenkov detectors spread over an area of 3000 km 2, overlooked by 24 wide-angle fluorescence telescopes placed in four sites on the array boundary. Southern Observatory is taking data in hybrid mode making it the first hybrid detector for studying the origin and the nature of cosmic rays at extreme energies. Current characteristics of the observatory and recent results on primary cosmic ray spectrum, arrival directions and composition are presented.

The Northern site of the Pierre Auger Observatory

To increase statistics for cosmic ray events with energies above 50EeV and to obtained a full sky coverage, a Northern Auger Observatory with a surface of 20,000km2 is planned in South East Colorado, USA. The design will use the well proven hybrid concept: a surface array combined with fluorescence telescopes. In this paper, the basic elements of Auger North will be described.

SiPM development for the imaging Cherenkov and fluorescence telescopes

A silicon photomultiplier (SiPM) is a novel solid state photodetector which has an outstanding photon counting ability. The device has excellent features such as high quantum efficiency (QE), good charge resolution, fast response (<100ps), very compact size, high gain (up to 2∼3×106), very low power consumption with low bias voltages (30∼70V), immunity to the magnetic field. In the last few years, UV sensitive SiPMs with a p-on-n structure have been developed by a few companies such as Hamamatsu, Photonique, Zecotek Photonics Inc., and institutes such as the MPI-HLL (Max-Planck-Institute for Physics—Max-Planck-Institute Semiconductor Laboratory) as well as the MPI-MEPhI (Max-Planck-Institute for Physics—Moscow Engineering Physical Institute). UV sensitive SiPMs are particularly promising for astroparticle physics applications in imaging atmospheric Cherenkov telescopes (IACTs), such as MAGIC/MAGIC-II [1] and CTA [2], and a fluorescence telescope in the space, JEM-EUSO [3].The current status of the SiPM development by MPI-HLL, MPI-MEPhI, and the study of the application to the telescopes noted above will be reported.

The northern site of the Pierre Auger Observatory

The Pierre Auger Observatory is an international facility dedicated to the full-sky study of the highest-energy cosmic rays. The southern site of the Auger Observatory was completed in June 2008. Data collected since January 2004 have yielded important information on the energy spectrum, the primary particle composition, the fluxes of photons and neutrinos and on the anisotropic distribution of the arrival directions of the most energetic particles. On this basis, the scientific motivation for the northern Auger Observatory site in Colorado, USA, is discussed. The overall layout, the key components and the expected performance of this 20 000 km2 hybrid observatory comprised of an array of 4400 surface detectors and 39 fluorescence telescopes are described.

Full simulation of space-based extensive air showers detectors with ESAF

Future detection of extensive air showers (EAS) produced by ultra high energy cosmic particles by means of space-based fluorescence telescopes will open a new window on the universe and allow cosmic ray and neutrino astronomy at a level that is virtually impossible for ground based detectors. In the context of the extreme universe space observatory (EUSO) project, an end-to-end simulation of EAS observation with a spatial detector has been designed (EUSO simulation and analysis framework, ESAF). This paper describes the detailed Monte-Carlo developed to simulate all the physical processes involved in the fluorescence detection technique, from the EAS development to the instrument response. Particular emphasis is given to modeling the light propagation in the atmosphere and the effect of clouds. The simulation is used to assess the performances of EAS spatial detection. Main results on energy threshold and resolution, direction resolution and X max determination are reported. Results are based on EUSO telescope design, but are also extended to larger and more sensitive detectors.

UHECR besides Cen A : Hints of galactic sources

Ultra High Energy Cosmic Rays, UHECR, maybe protons, as most still believe and claim, or nuclei; in particular lightest nuclei as we advocated recently. The two model offer a dramatic different view of the UHECR sky because different galactic Lorentz deflection and GZK cut-off. The first (Auger Collaboration) nucleon proposal (2007) Pierre Auger Collaboration (2007) [1] foresaw to trace clearly the UHECR GZK Universe reaching far (up to 100 Mpc) Super-Galactic-Plane, with little angular dispersion. On the contrary Lightest Nuclei model (2008) Fargion et al. (2008) [2], inspired by observed composition and by nearest Cen A clustering (almost a quarter of the AUGER events) explains (by cut off) a modest and narrow (few Mpc) Universe view, as well as the puzzling Virgo absence. The lightest nuclei offer a little blurred Astronomy. Here we address a part of the remaining scattered events in the new up-dated Auger map (March 2009-ICRC09). We found within the rarest clustering the surprising imprint of a few remarkable galactic sources. In particular we recognize a first trace of Vela, brightest gamma and radio galactic source, and smeared sources along the Galactic Plane and Center. We expect in the near future much more clustering along Cen A and a few more conforming to those galactic sources. The clustering may imply additional tails of fragments (by nuclei photo-dissociation) at half energies ( 2 – 4 ⋅ 10 19 eV ). The UHECR light-nuclei fragility and opacity may also reflect into a train of secondaries as gamma and neutrinos UHE events at tens or hundred PeVs. These UHE neutrinos might be detectable in the near future within the nearest AUGER and Array Fluorescence Telescope views, (few km distances), by the fast fluorescence flashing of horizontal up-going τ Air-showers.

Hybrid detection of ultra high energy cosmic rays with the Pierre Auger Observatory

The Pierre Auger Observatory has been designed to observe ultra high energy cosmic rays employing two independent techniques. It consists of a surface array overlooked by air fluorescence telescopes which together provide a powerful instrument for air shower reconstruction. The hybrid reconstruction approach and its performance are described and the hybrid detector exposure derived using an accurate simulation which takes into account the exact and time dependent working conditions of the experiment.

Measuring radio signals from extensive air showers

Understanding the origin and mechanism of production of the most energetic cosmic rays is one of the challenging questions of contemporary astroparticle physics. The extremely low flux of those particles does not permit direct measurements and observations are made via the cascade of secondary particles they initiate in the atmosphere, the so-called extensive air shower (EAS). Two techniques are used to perform such measurements: arrays of ground particle detectors and fluorescence telescopes. The latter offers a calorimetric measurement of the EAS but suffers a critical uptime of the order of 10%. The ground detector array is much more robust but Monte Carlo simulations are needed for energy calibration. The above considerations illustrate the pertinency of a new observation technique that could come in addition to the existing one to increase both statistics and EAS understanding in the field of ultra high energy cosmic rays (UHECR). The radio detection technique, which has known a renewal of interest in the last 5 years, might be an appropriate candidate. We will give a brief review of the historical concept, present the modern theoretical approaches and the current experiment based upon this principle of detection.

Radio detection of cosmic rays in the Pierre Auger Observatory

In small-scale experiments such as CODALEMA and LOPES, radio detection of cosmic rays has demonstrated its potential as a technique for cosmic ray measurements up to the highest energies. Radio detection promises measurements with high duty-cycle, allows a direction reconstruction with very good angular resolution, and provides complementary information on energy and nature of the cosmic ray primaries with respect to particle detectors at ground and fluorescence telescopes. Within the Pierre Auger Observatory, we tackle the technological and scientific challenges for an application of the radio detection technique on large scales. Here, we report on the results obtained so far using the Southern Auger site and the plans for an engineering array of radio detectors covering an area of ∼ 20 km 2 .

Detection of exotic massive hadrons in ultrahigh energy cosmic ray telescopes

We investigate the detection of exotic massive strongly interacting hadrons (uhecrons) in ultrahigh energy cosmic ray telescopes. The conclusion is that experiments such as the Pierre Auger Observatory have the potential to detect these particles. It is shown that uhecron showers have clear distinctive features when compared to proton and nuclear showers. The simulation of uhecron air showers, and its detection and reconstruction by fluorescence telescopes, is described. We determine basic cuts in observables that will separate uhecrons from the cosmic ray bulk, assuming this is composed by protons. If these are composed by a heavier nucleus, the separation will be much improved. We also discuss photon induced showers. The complementarity between uhecron detection in accelerator experiments is discussed.

Analysis of the fluorescence emission from atmospheric nitrogen by electron excitation, and its application to fluorescence telescopes

A microscopic analysis of the processes involved in the fluorescence emission of nitrogen molecules induced by electronic collisions is carried out for a large range of incident energies (eV to GeV) and pressures (Pa to atmospheric conditions). The contribution of secondary electrons to that fluorescence is calculated by means of detailed Monte Carlo simulations. For this purpose, a novel analytical approximation of the energy spectrum of secondary electrons is used. The results of the simulations are shown to be useful for the interpretation of available experimental data. For instance, they account for the pressure dependence of the fluorescence observed in laboratory experiments. The conditions under which emitted fluorescence is proportional to deposited energy are also studied. Finally, these calculations provide an absolute value of the fluorescence yield consistent with available experimental data.

On site calibration for new fluorescence detectors of the telescope array experiment

The Telescope Array experiment is searching for the origin of ultra-high energy cosmic rays using a ground array of particle detectors and three fluorescence telescope stations. The precise calibration of the fluorescence detectors is important for small systematic errors in shower reconstruction. This paper details the process of calibrating cameras for two of the fluorescence telescope stations. This paper provides the operational results of these camera calibrations.

Third level trigger for the fluorescence telescopes of the Pierre Auger Observatory

The trigger system for the Auger fluorescence telescopes is implemented in hard- and software for an efficient selection of fluorescence light tracks induced by high-energy extensive air showers. The algorithm of the third stage uses the multiplicity signal of the hardware for fast rejection of lightning events with above 99% efficiency. In a second step direct muon hits in the camera and random triggers are rejected by analyzing the space–time correlation of the pixels. The trigger algorithm was tested with measured and simulated showers and implemented in the electronics of the fluorescence telescopes. A comparison to a prototype trigger without multiplicity shows the superiority of this approach, e.g. the false rejection rate is a factor 10 lower.

A new numerical technique to determine primary cosmic ray composition in the ankle region

In this paper we introduce a new multiparametric technique that attempts to tackle simultaneously the problems of composition determination and hadronic interaction uncertainty. Employing simulations of a real world detector under its planned operational conditions, and disregarding systematics, we can asses that the present technique should be able to determine the composition of a binary mixture of p and Fe with a statistical confidence of few percent, in a way that is independent of the assumed hadronic interaction model. Moreover, the combination of real data with the tools developed and presented here should give an indication of the reliability of the various hadronic interaction models in current use in the area. We center our study in the region of the ankle, where composition carries critical astrophysical information, and use two main parameters: the number of muons at 600 m from the shower axis and the depth of the shower maximum obtained from the hybrid operation of the planned muon counters and high elevation fluorescence telescopes of the AMIGA and HEAT Auger enhancements.