A. Almela

An Indication of Anisotropy in Arrival Directions of Ultra-high-energy Cosmic Rays through Comparison to the Flux Pattern of Extragalactic Gamma-Ray Sources

A new analysis of the data set from the Pierre Auger Observatory provides evidence for anisotropy in the arrival directions of ultra-high-energy cosmic rays on an intermediate angular scale, which is indicative of excess arrivals from strong, nearby sources. The data consist of 5514 events above with zenith angles up to 80°xa0recorded before 2017 April 30. Sky models have been created for two distinct populations of extragalactic gamma-ray emitters: active galactic nuclei from the second catalog of hard Fermi-LAT sources (2FHL) and starburst galaxies from a sample that was examined with Fermi-LAT. Flux-limited samples, which include all types of galaxies from the Swift-BAT and 2MASS surveys, have been investigated for comparison. The sky model of cosmic-ray density constructed using each catalog has two free parameters, the fraction of events correlating with astrophysical objects, and an angular scale characterizing the clustering of cosmic rays around extragalactic sources. A maximum-likelihood ratio test is used to evaluate the best values of these parameters and to quantify the strength of each model by contrast with isotropy. It is found that the starburst model fits the data better than the hypothesis of isotropy with a statistical significance of 4.0σ, the highest value of the test statistic being for energies above . The three alternative models are favored against isotropy with 2.7σ–3.2σ significance. The origin of the indicated deviation from isotropy is examined and prospects for more sensitive future studies are discussed.

Digital electronics for the Pierre Auger Observatory AMIGA muon counters

The ``Auger Muons and Infill for the Ground Array (AMIGA) project provides direct muon counting capacity to the Pierre Auger Observatory and extends its energy detection range down to 0.3 EeV. It currently consists of 61 detector pairs (a Cherenkov surface detector and a buried muon counter) distributed over a 23.5 km2 area on a 750 m triangular grid. Each counter relies on segmented scintillator modules storing a logical train of `0s and `1s on each scintillator segment at a given time slot. Muon counter data is sampled and stored at 320 MHz allowing both the detection of single photoelectrons and the implementation of an offline trigger designed to mitigate multi-pixel PMT crosstalk and dark rate undesired effects. Acquisition is carried out by the digital electronics built around a low power Cyclone III FPGA. This paper presents the digital electronics design, internal and external synchronization schemes, hardware tests, and first results from the Observatory.

Analog multiplexer for testing multianode photomultipliers used in AMIGA project of the Pierre Auger Observatory

Most particle detectors used in astroparticle physics have an optoelectronic device that senses generated light and converts it into an electrical pulse. Photomultiplier tubes are commonly used, particularly those with multiple anodes. Prior to coupling to a detector system these tubes must be fully characterized, which requires either the same number of data acquisition channels as outputs or a switching-multiplexer system. Given that every project has its own requirements, the testing system must be as flexible as possible. The multiplexer presented here can be used to test silicon photomultipliers or any high-frequency signal. It is a scalable 64 to 4 channel analog device designed for low crosstalk and low attenuation. Results of the application of this multiplexer with a −3 dB bandwidth of 800 MHz are shown by testing 64-channel tubes for the AMIGA project.

Silicon photo-multipliers characterization system

Silicon photo-multipliers (SiPMs) are currently progressively replacing photo-multipliers tubes (PMTs) in most applications due to their technical advantages, specially in high energy physics experiments. This work describes a system to test photo-detectors in order to calibrate and characterize the parameters generally defined by scientific projects requirements. The system controls and monitors different variables, as temperature, bias, controlled light-source emission, and chamber humidity. It is included in this document the calibration results for a SensL MicroFC-SMA-30035 SiPM and its operation under working thermal conditions, such as the expected for an atmospheric Cherenkov telescope detector. First results show that the usage of this SiPM in a telescope is feasible concerning the expected thermal excursion.

AMIGA at the Auger observatory: the telecommunications system

AMIGA is an extension of the Pierre Auger Observatory that will consist of 85 detector pairs, each one composed of a surface water-Cherenkov detector and a buried muon counter. Each muon counter has an area of 30 square meters and is made of scintillator strips, with doped optical fibers glued to them, which guide the light to 64 pixel photomultiplier tubes. The detector pairs are arranged at 433 m and 750 m array spacings. In this paper we present the telecommunications system designed to connect the muon counters with the central data processing system at the observatory campus in Malargue. The telecommunications system consists of a point-to-multipoint radio link designed to connect the 85 muon counters or subscribers to two coordinators located at the Coihueco fluorescence detector building. The link provides TCP/IP remote access to the scintillator modules through router boards installed on each of the surface detectors of AMIGA. This setup provides a flexible LAN configuration for each muon counter connected to a WAN that links all the data generated by the muon counters and the surface detectors to the Central Data Acquisition System, or CDAS, at the observatory campus. We present the design parameters, the proposed telecommunications solution and the laboratory and field tests proposed to guarantee its functioning for the whole data traffic generated between each surface detector and muon counter in the AMIGA array and the CDAS.