Alberto Carraminana

New measurements of the 12. 6 millisecond pulsar in Cygnus X-3

Evidence for a 12.59 ms pulsar in Cygnus X-3 is presented on the basis of TeV gamma-ray observations. Evidence for pulsed emission at a phase in the 4.8 hr cycle and with a pulsar period and secular period derivative are compatible with earlier measurements (Chadwick et al., 1985). The conservative overall Rayleigh probability of uniformity of phase for this new result is 1.7 x 10 to the -6th. Data from observations of Cygnus X-3 from 1981 to 1985 are analyzed using a new X-ray ephemeris of the 4.8 hr X-ray cycle. This suggests that Cygnus X-3 is producing sporadic very high energy gamma rays at a fixed time in the 4.8 hr X-ray cycle. 28 refs.

Recent observations of VHE gamma rays from Cygnus X-3

The authors observations of Cygnus X-3 in 1981-88 have suggested that sporadic 12.6 ms pulsed very high energy gamma rays are produced at or near the maximum (phase 0.6) in the 4.8 h X-ray cycle. Cygnus X-3 was observed with the Durham University Mark IV Northern Hemisphere gamma-ray telescope in 1989, shortly after two radio outbursts were detected from the object. An analysis of these data suggests that 12.6 ms pulsar emission may be observed at a phase in the 4.8 h cycle some 1000 s before their prediction from previous measurements. This is in agreement with measurements made at Woomera by the University of Adelaide. More recent observations using the Mark III Southern Hemisphere telescope at large zenith angles have not provided any further evidence for pulsar activity.

The University of Durham Southern Hemisphere VHE gamma ray telescope

The design of very high energy (VHE) gamma ray telescopes is discussed and it is shown that a triple-mirror telescope operating in threefold fast coincidence provides an effective instrument. The design, construction and operation of a large VHE gamma ray telescope with an energy threshold of 300 GeV (at the zenith) and incorporating several novel features is described. The use of a coincidence ‘guard ring’ technique is shown to result in the rejection of about 50% of the off-source (proton) events which form a high background and limit the sensitivity of such telescopes.

VHE Gamma Ray Emission from Centaurus X-3

The high mass X-ray binary Centaurus X-3 has been observed using the Narrabri 250 GeV gamma ray telescope and the observations show evidence for pulsed VHE gamma ray emission, significant at the 4.2 SD level. The detected gamma ray signal in the total dataset comprises a broad pulse at precisely the contemporary X-ray period. The VHE emission is strongest for a few hours around the ascending node in the 2.1 d binary orbit. The time averaged energy flux in VHE gamma rays (> 250 GeV) is estimated to be ~ 1036 erg s-1 with a peak luminosity of 3×1036 erg s-1.

SN1987a - updated limit to 400 GeV gamma ray emission using the narrabri VHE gamma ray telescope - May 1989

Abstract A search for 400 GeV gamma rays from SN 1987a has been conducted using the Narrabri gamma ray telescope, starting with a fortuitous observation within 5 hours of the core collapse in 1987 February. A more extensive program of observations up to 1988 April has been reported by us 1 . A luminosity limit of 4 × 10 38 erg s −1 (significant at the 3 SD level) was obtained for the emission of gamma rays of energy > 400 GeV immediately following the collapse. Subsequent observations throughout 1987 indicate continued validity of this limit. In 1988 January–February, as the possibility of the penetration of VHE gamma rays increased, a series of observations provided a limit to the luminosity of 7×10 37 erg s −1 . We here report the results of continuing observations up to 1989 May.

TeV gamma rays from millisecond pulsars

We summarize here the results of the VHE gamma ray study of millisecond pulsars made over seven years by the Durham group. In addition to reporting observations made recently with the Mark III and IV telescopes at Narrabri, Australia, we consider the application of new analysis techniques to earlier data taken using telescopes at Dugway, USA. Pulsed VHE γ‐rays have been detected from three of the eight millisecond pulsars observed; we compare our results with the predictions of a theory of VHE emission from millisecond pulsars.

400 Gev gamma rays from the X-ray pulsar 1E2259+586

Abstract We report observations of the X-ray pulsar 1E2259+586 made in 1988 October using the very high energy gamma ray telescope operating in La Palma. We find evidence significant at the 5.3 × 10 −5 level for the emission of 400 GeV gamma rays pulsating at 6.9790s. The flux of gamma rays is (2.0 ± 0.8) × 10 −10 cm −2 s −1 corresponding to VHE gamma ray luminosity of (5.3 ± 2.1) × 10 35 erg s −1 .

Enhancement of the gamma ray signal in atmospheric Cerenkov light measurements using the University of Durham VHE gamma ray telescopes

Abstract The design of two types of very high energy (VHE) gamma ray telescope which have the capability to enhance the gamma ray signal is discussed. The performance of the array of Cerenkov light telescopes operated at Dugway from 1981 – 1984 to provide within field of view arrival direction measurements from inter telescope fast timing is assessed, and is compared with that of a large telescope now operating at Narrabri which has focal plane detectors incorporating a coincidence “guard ring” system. We conclude that the coincidence guard ring technique applied to a large collecting area telescope offers the greater sensitivity.