Gamma-ray Induced Air Showers Research Articles

Energy determination of gamma-ray induced air showers observed by an extensive air shower array

We propose a new energy estimator to determine the energies of gamma-ray induced air showers based on the lateral distribution of extensive air showers in the energy range between 10 TeV and 1000 TeV. We carry out a detailed Monte Carlo simulation assuming the Tibet air shower array located at an altitude of 4,300 m above sea level. We define S50, which denotes the particle density at 50 m from the air shower axis, as a new energy estimator. Using S50, the energy resolution is estimated to be approximately 16 % at 100 TeV in the range of the zenith angle 𝜃 < 20∘. We find S50 giving a better energy resolution than 27 % for the air shower size (N e) and 30 % for the sum of detected particles ( $\sum \rho $ ), which have been used so far, at 100 TeV. We also compare the reconstructed age distributions of gamma-ray induced air showers and hadronic cosmic-ray induced air showers. The age parameter may help to discriminate between primary gamma rays and hadronic cosmic rays.

Search for Galactic PeV gamma rays with the IceCube Neutrino Observatory

Gamma-ray induced air showers are notable for their lack of muons, compared to hadronic showers. Hence, air shower arrays with large underground muon detectors can select a sample greatly enriched in photon showers by rejecting showers containing muons. IceCube is sensitive to muons with energies above ∼500 GeV at the surface, which provides an efficient veto system for hadronic air showers with energies above 1 PeV. One year of data from the 40-string IceCube configuration was used to perform a search for point sources and a Galactic diffuse signal. No sources were found, resulting in a 90% C.L. upper limit on the ratio of gamma rays to cosmic rays of 1.2×10−3 for the flux coming from the Galactic plane region (−80°≲l≲−30°; −10°≲b≲5°) in the energy range 1.2–6.0 PeV. In the same energy range, point source fluxes with E−2 spectra have been excluded at a level of (E/TeV)2dΦ/dE∼10−12–10−11 cm−2 s−1 TeV−1 depending on source declination. The complete IceCube detector will have a better sensitivity (due to the larger detector size), improved reconstruction, and vetoing techniques. Preliminary data from the nearly final IceCube detector configuration have been used to estimate the 5-yr sensitivity of the full detector. It is found to be more than an order of magnitude better, allowing the search for PeV extensions of known TeV gamma-ray emitters.9 MoreReceived 30 October 2012DOI:https://doi.org/10.1103/PhysRevD.87.062002© 2013 American Physical Society

Selection and 3D-reconstruction of gamma-ray-induced air showers with a stereoscopic system of atmospheric Cherenkov telescopes

A simple 3D-reconstruction method for gamma-ray induced air showers is presented, which takes full advantage of the assets of a system of atmospheric Cherenkov telescopes combining stereoscopy and fine-grain imaging like the high energy stereoscopic system (HESS). The rich information collected by the cameras allows to select electromagnetic showers on the basis of their rotational symmetry with respect to the incident direction, as well as of their relatively small lateral spread. In the framework of a 3D-model of the shower, its main parameters – incident direction, shower core position on the ground, slant depth of shower maximum, average lateral spread of Cherenkov photon origins (or “photosphere 3D-width”) and primary energy – are fitted to the pixel contents of the different images. For gamma-ray showers, the photosphere 3D-width is found to scale with the slant depth of shower maximum, an effect related to the variation of the Cherenkov threshold with the altitude; this property allows to define a dimensionless quantity ω (the “reduced 3D-width”), which turns out to be an efficient and robust variable to discriminate gamma-rays from primary hadrons. In addition, the ω distribution varies only slowly with the gamma-ray energy and is practically independent of the zenith angle. The performance of the method as applied to HESS is presented. Depending on the requirements imposed to reconstructed showers, the angular resolution at zenith varies from 0.04° to 0.1° and the spectral resolution in the same conditions from 15% to 20%.

The STACEE ground-based gamma-ray detector

We describe the design and performance of the Solar Tower Atmospheric Cherenkov Effect Experiment (STACEE) in its complete configuration. STACEE uses the heliostats of a solar energy research facility to collect and focus the Cherenkov photons produced in gamma-ray induced air showers. The light is concentrated onto an array of photomultiplier tubes located near the top of a tower. The large Cherenkov photon collection area of STACEE results in a gamma-ray energy threshold below that of previous ground-based detectors. STACEE is being used to observe pulsars, supernova remnants, active galactic nuclei, and gamma-ray bursts

The STACEE-32 ground based gamma-ray detector

We describe the design and performance of the Solar Tower Atmospheric Cherenkov Effect Experiment detector in its initial configuration (STACEE-32). STACEE is a new ground-based gamma-ray detector using the atmospheric Cherenkov technique. In STACEE, the heliostats of a solar energy research array are used to collect and focus the Cherenkov photons produced in gamma-ray induced air showers. The large Cherenkov photon collection area of STACEE results in a gamma-ray energy threshold below that of previous detectors.

Observation of the Crab Nebula with an ultraviolet Cherenkov camera

Gamma-ray astronomy at energies of a few hundred GeV is now well established, with the observation of emission from the Crab Nebula by at least five independent groups. The technique is based on the detection of the Cherenkov light emitted by gamma-ray induced air showers. It requires clear, moonless nights, which seriously curtail the useful duty cycle. It is shown here that by detecting the UV Cherenkov photons instead of the full visible Cherenkov spectrum, the observations can be extended to moonlit nights, with lower constraints on the background light from the moon and stars, but with a somewhat higher energy threshold.