The Pierre Auger Observatory is the world’s largest cosmic ray observatory. Our current exposure reaches nearly 40,000 km
2
sr and provides us with an unprecedented quality data set. The performance ...and stability of the detectors and their enhancements are described. Data analyses have led to a number of major breakthroughs. Among these, we discuss the energy spectrum and the searches for large-scale anisotropies. We present analyses of our
X
max
data and show how it can be interpreted in terms of mass composition. We also describe some new analyses that extract mass-sensitive parameters from the 100 % duty cycle surface detector (SD) data. A coherent interpretation of all these recent results opens new directions. The consequences regarding the cosmic ray composition and the properties of ultrahigh-energy cosmic ray (UHECR) sources are briefly discussed.
Radio emission from the extensive air showers (EASs), initiated by ultrahigh-energy cosmic rays, was theoretically suggested over 50 years ago. However, due to technical limitations, successful ...collection of sufficient statistics can take several years. Nowadays, this detection technique is used in many experiments consisting in studying EAS. One of them is the Auger Engineering Radio Array (AERA), located within the Pierre Auger Observatory. AERA focuses on the radio emission, generated by the electromagnetic part of the shower, mainly in geomagnetic and charge excess processes. The frequency band observed by AERA radio stations is 30-80 MHz. Thus, the frequency range is contaminated by human-made and narrow-band radio frequency interferences (RFIs). Suppression of contaminations is very important to lower the rate of spurious triggers. There are two kinds of digital filters used in AERA radio stations to suppress these contaminations: the fast Fourier transform median filter and four narrow-band IIR-notch filters. Both filters have worked successfully in the field for many years. An adaptive filter based on a least mean squares (LMS) algorithm is a relatively simple finite impulse response (FIR) filter, which can be an alternative for currently used filters. Simulations in MATLAB are very promising and show that the LMS filter can be very efficient in suppressing RFI and only slightly distorts radio signals. The LMS algorithm was implemented into a Cyclone V field programmable gate array for testing the stability, RFI suppression efficiency, and adaptation time to new conditions. First results show that the FIR filter based on the LMS algorithm can be successfully implemented and used in real AERA radio stations.
Neutrinos play a fundamental role in the understanding of the origin of ultrahigh-energy cosmic rays. They interact through charged and neutral currents in the atmosphere generating extensive air ...showers. However, the very low rate of events potentially generated by neutrinos is a significant challenge for detection techniques and requires both sophisticated algorithms and high-resolution hardware. Air showers initiated by protons and muon neutrinos at various altitudes, angles, and energies were simulated in CORSIKA and the Auger OffLine event reconstruction platforms, giving analog-to-digital convertor (ADC) patterns in Auger water Cherenkov detectors on the ground. The proton interaction cross section is high, so proton "old" showers start their development early in the atmosphere. In contrast to this, neutrinos can generate "young" showers deeply in the atmosphere relatively close to the detectors. Differences between "old" proton and "young" neutrino showers are visible in attenuation factors of ADC waveforms. For the separation of "old" proton and "young" neutrino ADC traces, many three-layer artificial neural networks (ANNs) were tested. They were trained in MATLAB (in a dedicated way -only "old" proton and "young" neutrino showers as patterns) by simulated ADC traces according to the Levenberg-Marquardt algorithm. Unexpectedly, the recognition efficiency is found to be almost independent of the size of the networks. The ANN trigger based on a selected 8-6-1 network was tested in the Cyclone V E FPGA 5CEFA9F31I7, the heart of prototype front-end boards developed for testing new algorithms in the Pierre Auger surface detectors.
Seven front-end boards (FEBs) equipped with the biggest Cyclone V E field-programmable gate array (FPGA) 5CEFA9F31I7N supporting eight channels sampled up to 250 MS/s at 14-bit resolution have been ...successfully installed in seven surface detectors (SDs) on the Pierre Auger Test Array. SDs use six channels with a sampling of 120 MHz. Two remaining channels with independent sampling at a 200-MHz rate were tested as radio channels. The FEBs have been developed without antialiasing filters to keep a maximal flexibility. Communication between SDs and the central data acquisition system (CDAS) has been established via a standard radio link without any modification of a standard protocol. Any tuning of required processes, typically being a task of the unified board, has been moved to the FPGA algorithm. The power consumption by the new FEBs is at the level of 18 W, but the average solar panel output power is ~10 W. An external power control circuit (with a hysteresis cut OFF/ON) supplies the entire SD electronics to avoid a total battery discharge and the possible damage this may cause. Such an interrupted operation reduces significantly the statistics of events recorded while a second (or larger) solar panel would eliminate this inconvenience, we gather experience here under realistic conditions on the Argentine pampas, including the reduced amount of available power. We installed seven FEBs in the Pierre Auger Test Array in November 2015. Data acquisition is going smoothly on the primary Auger (T1) trigger only. The time-over-threshold trigger has not been implemented due to instabilities.
The Pierre Auger Observatory is the largest extensive air shower detector, covering 3000 km2 in Argentina. The Observatory makes available, for educational and outreach purposes, 1% of its cosmic ray ...data set, corresponding after 10 years of running to more than 35 000 cosmic ray events. Several different proposals of educational activities have been developed within the collaboration and are available. We will focus on the activity guide we developed with the aim of exploring the rich education and outreach potential of cosmic rays with Portuguese high school students. In this guide we use the Auger public data set as a starting point to introduce open questions on the origin, nature and spectrum of high energy cosmic rays. To address them, the students learn about the air-shower cascade development, data reconstruction and its statistical analysis. The guide has been used both in the context of student summer internships at research labs and directly in schools, under the supervision of trained teachers and in close collaboration with Auger researchers. It is now available in Portuguese, English and Spanish.
The trigger based on the Discrete Cosine Transform (DCT) allows recognition of ADC traces of a specific shape i.e., with a very short rise time and fast exponential attenuation related to a narrow, ...flat muon component of very inclined extensive air showers generated by hadrons and starting their development early in the atmosphere ("old" showers). Showers, crossing a surface detector composed of water Cherenkov tanks, such as those in the Pierre Auger Observatory generate Cherenkov light, which may hit photomultipliers (PMTs) directly or after several reflections. The geometry of the water Cherenkov tank imposes a type of the filter preferring the detection of very inclined showers (with very large zenith angle), where mainly two PMTs can be hit by direct light. The 3rd PMT is then hit by reflected light, but with some delay. For the fast sampling (80 MHz), this delay causes the signal to appear in the next time bin. Two-fold coincidences of DCT coefficients allow triggering signals that are ignored at that time due to either too high an amplitude threshold for three-fold coincidences in a single time bin (the standard Auger threshold trigger) or due to the de-synchronization of the signals in time caused by the tank geometry (delay on one or more time bins due to a longer light path corresponding to the reflection on the tank walls). Three DCT engines implemented into EP3C40F324I7 FPGA use all DSP blocks and generate the spectral trigger, when 8 DCT coefficients simultaneously are inside the acceptance lane in at least 2 channels. An additional veto signal (analyzing the amplitude) controls the trigger rate to avoid a saturation of a transmission channel. In a test performed in the Pierre Auger laboratory in Malargue (Argentina), the spectral trigger has been tuned for shapes corresponding to "old" showers. Both laboratory and long-term field measurements on a test tank confirmed a high efficiency of the recognition of expected patterns of ADC traces. The patterns of the spectral trigger for "young" showers are being optimized in simulations. We expect to detect "young" showers close to their cores.
We present first results from a trigger based on the discrete cosine transform (DCT) operating in new front-end boards with a Cyclone V E field-programmable gate array (FPGA) deployed in seven test ...surface detectors in the Pierre Auger Test Array. The patterns of the ADC traces generated by very inclined showers (arriving at 70° to 90° from the vertical) were obtained from the Auger database and from the CORSIKA simulation package supported by the Auger OffLine event reconstruction platform that gives predicted digitized signal profiles. Simulations for many values of the initial cosmic ray angle of arrival, the shower initialization depth in the atmosphere, the type of particle, and its initial energy gave a boundary on the DCT coefficients used for the online pattern recognition in the FPGA. Preliminary results validated the approach used. We recorded several showers triggered by the DCT for 120 Msamples/s and 160 Msamples/s.
The radio detector system for ultrahigh-energy cosmic rays in the Pierre Auger Observatory operates in the frequency range 30-80 MHz, which is often contaminated by human-made radio-frequency ...interferences (RFIs). Several filters were used to suppress the RFI: based on the FFT, an IIR notch filter, and an FIR filter based on the linear prediction. The last refreshes the FIR coefficients calculating either in the external ARM processor, internal soft-core NIOS processor implemented inside the field programmable gate aray (FPGA), or hardcore embedded processors based on Integrated ARM CortexA9800 MHz Hardcore Processor System (HPS) being a silicon part of the FPGA chip. Refreshment times significantly depend on the type of calculation process. For a stationary RFI, the FIR coefficients can be refreshed each minute or rarer. However, an efficient suppression of nonstationary short-term contaminations requires a much faster response. Calculations of FIR coefficients in an external Voipac PXA270M ARM processor take 1-2 s, by the soft-core virtual NIOS processor on the level of hundreds of milliseconds. The HPS allows a reduction of the refreshment time to ~20 ms (for a 32-stage FIR filter). A symmetry of covariance matrix allows one to use the much faster Levinson procedure instead of typical Gauss routine for solving a set of linear equations of time. A hardware implementation of this procedure inside the FPGA fabric as a specialized μC (with 100-MHz clock) requires only ~53800 clock cycles. We used 64or 48-b floating-point representations to calculate FIR coefficients. Resources occupation is relatively high, as the design was optimized for a maximal register performance. However, the RFI suppression is very efficient. We expect a significant suppression of even a short-term nonstationary RFI.
Experiments which observe coherent radio emission from extensive air showers induced by ultra-high energy cosmic rays are designed for a detailed study of the development of the electromagnetic part ...of air showers. Radio detectors can operate with 100% up time as e.g. surface detectors based on water-Cherenkov tanks. They are being developed for ground-based experiments (e.g. the Pierre Auger Observatory) as another type of air shower detector in addition to fluorescence detectors, which operate with only ~ 10% of duty on dark nights. The radio signals from air showers are caused by coherent emission caused by geomagnetic radiation and charge excess processes. The self-triggers currently used in radio detectors often generate a dense stream of data, which is analyzed afterwards. Large amounts of stored data require significant computing resources for off-line analysis. An improvement of the trigger efficiency would be highly desirable. A wavelet trigger, which investigates the power of radio signals ( ~ V 2 /R) on-line is a promising development of the current designs. In this work, Morlet wavelets with various scaling factors were used for an analysis of real data from the Auger Engineering Radio Array (AERA) and for an optimization of the utilization of the resources in an FPGA. The wavelet analysis showed that the power of events is concentrated mostly in a limited range of the frequency spectrum (consistent with a range imposed by the input analog band-pass filter). However, we found several events with suspicious spectral characteristics, where the signal power was spread over the full band-width sampled by a 200 MHz digitizer with a significant contribution from very high and very low frequencies. These events most probably do not originate from cosmic ray showers but could be human-made contaminations. The engine of a wavelet analysis can be implemented in the modern powerful FPGA and can remove suspicious events on-line to reduce the trigger rate.
PDF
