Observation of Multi-T[CLC]e[/CLC]V Gamma Rays from the Crab Nebula using the Tibet Air Shower Array

Abstract

The Tibet experiment, operating at Yangbajing (4300 m above sea level), is the lowest energy air shower array, and the new high-density array constructed in 1996 is sensitive to gamma-ray air showers at energies as low as 3 TeV. With this new array, the Crab Nebula was observed in multi-TeV gamma-rays and a signal was detected at the 5.5 sigma level. We also obtained the energy spectrum of gamma-rays in the energy region above 3 TeV which partially overlaps those observed with imaging atmospheric Cerenkov telescopes. The Crab spectrum observed in this energy region can be represented by the power-law fit dJ&parl0;E&parr0;&solm0;dE=&parl0;4.61+/-0.90&parr0;x10-12&parl0;E&solm0;3 TeV&parr0;-2.62+/-0.17 cm-2 s-1 TeV-1. This is the first observation of gamma-ray signals from point sources with a conventional air shower array using scintillation detectors.

Teraelectronvolt Astronomy

“…In addition, whilst in principle all-sky detectors, the field of view obtained is limited in practice by the rapid increase in energy threshold with zenith angle; typically a factor two increase between 0 MILAGRO achieves its best background rejection power and sensitivity in the regime above 10 TeV. Widely spaced (∼1 m 2 detectors > 5 m apart) scintillationbased detectors have been used for CR measurements and in the search for UHE γ-ray sources for many years Instruments of this type located at high altitudes can be used for γ-ray astronomy around a few TeV, as demonstrated with the Tibet Air-Shower Array (Amenomori et al 1999) at 4300 m above sea level. The ARGO-YBJ instrument is a 5800 m 2 complete ground coverage instrument at the same site, utilizing resistive plate counters (RPCs) and achieving a threshold of a few hundred GeV and a sensitivity similar to that of MILAGRO.…”

VHE γ‐Ray Observation of the Crab Nebula and its Pulsar with the MAGIC Telescope

“…Since its discovery, detailed studies of the VHE emission energy spectrum, ranging from several hundred GeV up to 80 TeV, have been carried out (e.g. Akerlof et al 1990;Vacanti et al 1991;Baillon et al 1991;Goret et al 1993;Konopelko et al 1996;Tanimori et al 1998;Hillas et al 1998;Amenomori et al 1999;Majumdar et al 2002;Aharonian et al 2004Aharonian et al , 2006. Between 10 and ∼ 200 GeV, observations are sparse.…”

Ground-based detectors in very-high-energy gamma-ray astronomy

“…Such detectors are usually installed at high altitude to collect more charged particles. Several types of particle samplers have been tried, including scintillator arrays [7], resistive plate chamber carpets [8] and water Cherenkov ponds [9,10,11]. A sketch of the Milagro water Cherenkov detector is shown in Fig.…”