Ground-based very high energy gamma ray astronomy: Observational highlights

It is now more than 20 years since the first ground based gamma ray experiments involving atmospheric Cerenkov radiation were undertaken. The present highlights in observational ground-based very high energy (VHE) gamma ray astronomy and the optimism about an interesting future for the field follow progress in these areas: (1) the detection at increased levels of confidence of an enlarged number of sources so that at present claims were made for the detection, at the 4 to 5 sd level of significance, of 8 point sources; (2) the replication of the claimed detections with, for the first time, confirmation of the nature and detail of the emission; and (3) the extension of gamma ray astronomy to the ultra high energy (UHE) domain. The pattern, if any, to emerge from the list of sources claimed so far is that X-ray binary sources appear to be copious emitters of gamma rays over at least 4 decades of energy. These X-ray sources which behave as VHE and UHE gamma ray emitters are examined

The 1000 GeV gamma ray emission from radio pulsars

Radio pulsars have concentrated on long observations of the Crab pulsar and showed that it emits short intense bursts and a persistent weak periodic flux at gamma-ray energies 1000 GeV. It was shown that the light curve of the persistent emission was dominated by a single peak, coincident with the position of the radio and low energy gamma-ray main pulse. The results of a more detailed analysis of the structure of this main pulse are reported following an appraisal of the timing system. It is shown that at energies 1000 GeV the duration of the main pulse is not greater than 0.4 ms, which is less than that seen at all frequencies other than radio. Flux limits for the emission of 1000 GeV gamma-rays by seven other radio pulsars are reporte

The 1000 GeV gamma rays from ms pulsars

The detection of 1000 GeV gamma-rays with the characteristic 6.1 ms periodicity of the radio pulsar PSR 1953 +29 is reported. This result, significant at the 5.4 beta level, provides the first direct evidence for the association of the 6 ms radio pulsar PSR1953+29 with the gamma-ray source 2CG065+0. Extensive observations of the 1.5 ms pulsar PSR 1937 are also reported

1000 GeV gamma rays from Cygnus X-3: An update

Measurements of 1000 GeV gamma-rays from Cygnus X-3 made with the University of Durham facility at Dugway, Utah in 1981/82 are reviewed. The light curve of the 4.8 hour modulated emission is updated and shows evidence significant at the 4.4 sigma level for strong emission (9% of the cosmic ray rate) at phase 0.625 and less significant (1.4 sigma level) indications of weaker emission (3% of the cosmic ray rate) at phase 0.125. The effect constituting the excess on the few nights showing the strongest emission appears to arise from the smallest Cerenkov light signals suggesting a steep gamma-ray spectrum. The 1982 data have been searched unsuccessfully for evidence of emission at phase 0.2, in coincidence with the results from the ultra-high energy (extensive Air Showers (EAS) measurements in 1979-1982. A systematic investigation of a long term variation in the strength of the peak of the 4.8 hr modulated 1000 GeV gamma-ray emission has been made. We find that in addition to the approximately 34 d variation reported by us previously, a stronger effect exists at around 19d