D. Hampf

Event reconstruction techniques for the wide-angle air Cherenkov detector HiSCORE

Wide-angle, non-imaging air Cherenkov detectors provide a way to observe cosmic gamma-rays which is complementary to observations by imaging Cherenkov telescopes. Their particular strength lies in the multi-TeV to ultra high energy range (Eγ>30TeV), where large effective areas, yet small light sensitive areas per detector station are needed. To exploit this potential to full extent, a large station spacing is required to achieve a large effective area at a reasonable effort. In such a detector, the low number of signals per event, the absence of imaging information, and the poor signal to noise ratio of Cherenkov light to night sky brightness pose considerable challenges for the event reconstruction, especially the gamma hadron separation. The event reconstruction presented in this paper has been developed for the wide-angle detector HiSCORE, but the concepts may be applied more generically. It is tested on simulated data in the 10 TeV to 5 PeV energy range using the air shower simulation CORSIKA and the HiSCORE detector simulation sim_score. For the tests, a regular grid of 22×22 detector stations with a spacing of 150 m is assumed, covering an area of 10 km2. The angular resolution of individual events is found to be about 0.3° near the energy threshold, improving to below 0.1° at higher energies. The relative energy resolution is 20% at the threshold and improves to 10% at higher energies. Several parameters for gamma hadron separation are described. With a combination of these parameters, 80–90% of the hadronic background can be suppressed, while about 60% of the gamma-ray events are retained. The point source sensitivity to gamma-ray sources is estimated, using conservative assumptions, to be about 8×10−13ergs−1cm−2 at 100 TeV gamma-ray energy for a 10 km2 array. With more optimistic assumptions, and a 100 km2 array, a sensitivity of about 1×10−13ergs−1cm−2 can be achieved (at 100 TeV). Even in the former case the detector is sensitive enough to measure the continuation of currently known gamma-ray spectra into the ultra high energy domain. Due to its large field of view of 0.6 sr it also offers a great potential for the discovery of new gamma-ray sources at the so far largely unexplored energies of 100 TeV and above.

HiSCORE - The Hundred*i square-km cosmic ORigin explorer

Addressing the mysteries of cosmic rays requires a comprehensive observational approach, including information on mass composition and spectrum (from CR nuclei) as well as directional information (gamma-rays or neutrinos). HiSCORE covers both approaches using indirect air-shower observations of cosmic rays from 100 TeV to 1 EeV and gamma-rays in the so far poorly covered energy range from 10 TeV to several PeV. Among other questions of astroparticle and particle physics, HiSCORE will allow cosmic ray composition and spectral measurements in the transition range between Galactic and Extragalactic origin. Searching for gamma-rays from the PeV-accelerators, the pevatrons, will consititute a crucial building-block for solving the question of the origin of Galactic cosmic rays. HiSCORE is an array of non-imaging light-collecting stations for Cherenkov light-front sampling. The lateral Cherenkov photon density and arrival-time distribution are measured, allowing the reconstruction of the direction, the energy, ...

Simulation of the expected performance for the proposed gamma-ray detector HiSCORE

The HiSCORE project aims at opening up a new energy window in gamma-ray astronomy: The energy range above 30 TeV and up to several PeV. For this, a new detector system is being designed. It consists of a large array of non-imaging Cherenkov detectors with a light sensitive area of 0.5 square metres each. The total effective area of the detector will be 100 square kilometres. A large inter-station distance of 150 metres and a simple and inexpensive station design will make the instrumentation of such a large area feasible. A detailed detector simulation and event reconstruction system has been developed and used in conjunction with the CORSIKA air-shower simulation to estimate the sensitivity of the detector to gamma-ray point sources. The threshold for gamma-rays is 44 TeV (50% trigger efficiency) in the standard configuration, and the minimal detectable flux from a point source is below 10^(-13) erg / (s cm^2) above 100 TeV. Several options to lower the energy threshold of the detector have been examined. The threshold is decreased to 34 TeV by a smaller station spacing of 100 metres, and is further decreased to 24 TeV if the detector is set up at an altitude of 2000 metres above sea level. At a spacing of 150 metres, however, a higher altitude has no positive effect on the energy threshold. The threshold can also be reduced if the detector stations consist of small, independent 2 x 2 sub-arrays. In this case, the station spacing is not significant for the threshold, but again a higher altitude decreases the threshold further.

The HiSCORE Project

A central question of Astroparticle Physics, the origin of cosmic rays, still remains unsolved. HiSCORE (Hundred*i Square-km Cosmic ORigin Explorer) is a concept for a large-area wide-angle non-imaging air shower detector, addressing this question by searching for cosmic ray pevatrons in the energy range from 10TeV to few PeV and cosmic rays in the energy range above 100TeV. In the framework of the Tunka-HiSCORE project, first prototypes have been deployed on the site of the Tunka-133 experiment, where we plan to install an engineering array covering an area of the order of 1km 2 . On the same site, also imaging and particle detectors are planned, potentially allowing a future hybrid detector system. Here we present the HiSCORE detector principle, its potential for cosmic ray origin search and the status of ongoing activities in the framework of the Tunka-HiSCORE experiment.

The HiSCORE experiment and its potential for gamma-ray astronomy

The HiSCORE (Hundred*i Square-km Cosmic ORigin Explorer) detector aims at the exploration of the accelerator sky, using indirect air-shower observations of cosmic rays from 100 TeV to 1 EeV and gamma rays in the last remaining observation window of gamma-ray astronomy from 10 TeV to several PeV. The main questions addressed by HiSCORE are cosmic ray composition and spectral measurements in the Galactic/extragalactic transition range, and the origin of cosmic rays via the search for gamma rays from Galactic PeV accelerators, the pevatrons. HiSCORE is based on non-imaging Cherenkov light-front sampling with sensitive large-area detector modules of the order of 0.5 m2. A prototype station was deployed on the Tunka cosmic ray experiment site in Siberia, where an engineering array of up to 1km2 is planned for deployment in 2012/2013. Here, we address the expected physics potential of HiSCORE, the status of the project, and further plans.

First deployment and prototype data of HiSCORE

With the HiSCORE (Hundred*i Square kilometer Cosmic ORigin Explorer) experiment we aim at the exploration of the accelerator sky using indirect air shower observations of cosmic rays from 100 TeV to 1 EeV and gamma rays above 10 TeV to several PeV. In this paper the HiSCORE detector is discribed and the results of the first prototype deployment are shown. Several components are discussed like the photomultiplier tubes, the clip-sum-trigger and the DRS4 based data acquisition. We present data taken with a first prototype station in April 2012 at Tunka.

Discovery of gamma-ray emission from the extragalactic pulsar wind nebula N157B with the High Energy Stereoscopic System

We present the significant detection of the first extragalactic pulsar wind nebula (PWN) detected in gamma rays, N157B, located in the large Magellanic Cloud (LMC). Pulsars with high spin-down luminosity are found to power energised nebulae that emit gamma rays up to energies of several tens of TeV. N157B is associated with PSRJ0537-6910, which is the pulsar with the highest known spin-down luminosity. The High Energy Stereoscopic System telescope array observed this nebula on a yearly basis from 2004 to 2009 with a dead-time corrected exposure of 46 h. The gamma-ray spectrum between 600 GeV and 12 TeV is well-described by a pure power-law with a photon index of 2.8 \pm 0.2(stat) \pm 0.3(syst) and a normalisation at 1 TeV of (8.2 \pm 0.8(stat) \pm 2.5(syst)) \times 10^-13 cm^-2s^-1TeV^-1. A leptonic multi-wavelength model shows that an energy of about 4 \times 10^49erg is stored in electrons and positrons. The apparent efficiency, which is the ratio of the TeV gamma-ray luminosity to the pulsars spindown luminosity, 0.08% \pm 0.01%, is comparable to those of PWNe found in the Milky Way. The detection of a PWN at such a large distance is possible due to the pulsars favourable spin-down luminosity and a bright infrared photon-field serving as an inverse-Compton-scattering target for accelerated leptons. By applying a calorimetric technique to these observations, the pulsars birth period is estimated to be shorter than 10 ms.

The hardware of the HiSCORE γ-ray and cosmic ray Cherenkov detector

The HiSCORE (Hundred Square km Cosmic ORigin Explorer) project is a ground-based large-area wideangle air shower detector array that will measure gamma rays and cosmic rays in the energy range of 10 TeV up to 1EeV. Each detector array station consists of four separate light collectors with an 8-inch photomultiplier (PMT) at each end. The first station prototype has already been deployed to Tunka valley. On-site station integration and first measurements have been made. This poster will focus on the hardware aspects and the first light results of the single station.