M. R. Dickinson

TeV gamma rays from PSR 1706-44

Observations made with the University of Durham Mark 6 atmospheric Cerenkov telescope conrm that PSR B1706-44 is a very high energy -ray emitter. There is no indication from our dataset that the very high energy -rays are pulsed, in contrast to the ndings at 300 GeV is estimated to be (3:90:7stat)10 11 cm 2 s 1 .

Centaurus X-3: A Source of High-Energy Gamma Rays

Centaurus X-3 is a well studied high-mass accreting X-ray binary and a variable source of high-energy gamma rays with energies from 100 MeV to 1 TeV. Previous results have suggested that the origin of the gamma rays is not the immediate vicinity of the neutron star but is sited in the accretion disk, perhaps in an accretion wake. The Durham Mark 6 gamma-ray telescope has been used to measure the gamma-ray flux from Centaurus X-3 with much higher sensitivity than previous ground-based measurements. The flux above ~400 GeV was measured to be (2 ± 0.3) × 10-11 cm-2 s-1 and appears constant over a period of 2-3 months. In 10 hours of observations there is no evidence for periodicity in the detected gamma rays at the X-ray spin period either from a site in the region of the neutron star or from any other potential site in the orbit.

A burst of pulsed VHE gamma rays from AE Aquarii

Abstract We report the results of observations of AE Aquarii made on 25 occasions between July 1992 and October 1993 with the University of Durham very high energy (VHE) gamma-ray telescopes at Narrabri, N.S.W., Australia. The observations lasted for a total of 78 h and no persistent low-level pulsed emission was detected above an energy threshold of 350 GeV. However, an excess of pulsed VHE γ-rays was observed on 1993 October 11. The burst lasted for approximately 4200 s and occurred at phase 0.62–0.74 in the 9.88 h orbital cycle. The count rate excess was significant at the 0.99997 level and the periodicity was at the second harmonic of the 33 s period The hadron-induced background in the burst data has been suppressed by applying simple imaging techniques to those events recorded by an individual telescope and using trigonometric height of maximum analysis for the events recorded by two telescopes. These two independent results together provide evidence at a probability of chance occurrence of 10−7, after allowing for degrees of freedom, for the emission of a burst of pulsed γ-rays from AE Aquarii with threshold energy > 350 GeV, which show the characteristic features of γ-ray induced cascades. There is also some evidence to suggest that the brightness spectrum of Cerenkov events recorded during the burst is harder than that recorded in a sample of the background. The flux during the burst was approximately 4% of the total cosmic ray background at E> 350 GeV, corresponding to a peak pulsed luminosity of 1032 erg s−1

The University of Durham Mark 6 Gamma Ray Telescope

The design, construction and operation of the University of Durham ground-based gamma ray telescope is discussed. The telescope has been designed to detect gamma rays in the ≤ 200 GeV region and to achieve good discrimination between gamma ray and hadron initiated showers in the higher energy region (≳ 300 GeV). The telescope was commissioned in 1995 and a description of its design and operation is presented, together with a verification of the telescopes performance.

The University of Durham Mark 6 VHE gamma ray telescope

The operation of the University of Durham Mark 6 atmospheric Cerenkov telescope is discussed. The telescope has been used to detect gamma rays at energies ⩾150 GeV and to achieve good discrimination between gamma ray and hadron initiated showers, using both conventional imaging and novel fluctuation measures. The telescope was commissioned in 1995 and a description of its operation is presented. Verification of the performance during observations of PSR B1706-44 is described.

VHE gamma rays from PSR B1706-44

Observations made with the University of Durham Mark 6 atmospheric Cerenkov telescope confirm that PSR B1706-44 is a VHE γ-ray emitter. The γ-ray flux has been measured at 250 GeV, and suggests a spectral slope that is consistent with extrapolation from the sub-10 GeV region. There is no indication from our dataset that the VHE γ-rays are pulsed, in contrast to the findings at <20 GeV, which indicate that 100% of the flux is pulsed.