J. A. Gaidos

The Haleakala gamma ray observatory

A 10 m2 multi-mirror telescope for observing Cherenkov light signals from atmospheric cascades is now operating at Mount Haleakala, Maui, Hawaii. It differs from other atmospheric Cherenkov detectors in accepting pulses that originate from single photoelectrons, employing two sets of 18 optically independent phototubes in a logic system with nanosecond time resolution to reject ambient light from the night sky. With an angular aperture of 1.3 × 10−4 sr, cosmic ray showers are observed at a rate of ∼ 0.5 hz at the zenith, with nearly complete rejection of ambient light. This rate for hadronic showers implies an effective threshold near 100 GeV for electromagnetic showers. Two regions of the sky, one centered on the source and the other separated by from it by 3.6° are simultaneously monitored. Examples of observations of episodic and periodic (pulsar) sources are given.

The Haleakala Gamma Observatory

The Haleakala Gamma Observatory is a 10m2 multi-mirror telescope for observing Cherenkov light from electromagnetic cascades in the atmosphere. It is situated at an altitude of 2950 meters at 20.7°N, 156°W on Mount Haleakala, Maui, Hawaii. It differs from most Cherenkov devices in accepting single photoelectron pulses. It employs two sets of 18 phototubes observing seperate regions of the sky to continuously monitor hadronic background. Hardware coincidence resolution is 10ns, and digital filtering can reduce this substantially, effectively eliminating random signals from ambient light. Events are timed to within ±2μs of UTC by a Cesium beam atomic clock. Hadronic showers are observed at rates of 0.5 to 0.7 Hz, implying a threshold for gamma-induced showers of about 200 GeV.

VHE GAMMA RAYS FROM CYGNUS X-3

The Haleakala 10 m2 Cherenkov light telescope observed Cyg X-3 for 113 hours during the summer and fall of 1985. A 60-sec. burst of gamma rays was observed during the radio flare of early Oct. at a phase of o BB = 0.74. No evidence for pulsar periodicity was found during the burst. Searches for periodicity outside the burst have not yet produced positive results.

VHE gamma-ray studies at the Haleakala gamma observatory

Abstract Data collected with the Cerenkov telescope at the Haleakala Gamma Observatory have been analyzed in an effort to establish evidence for emission of VHE γ-rays for a number of candidate sources. Brief episodes of emission from Her X-1 have been detected. The results from searches for emission from other sources, which has not been detected by our group, are discussed. Continued observations with an upgraded telescope facility are currently underway.

TeV atmospheric Cherenkov telescope at the South Pole

Abstract A collaboration has formed to design and construct an atmospheric Cherenkov telescope to be located at the South Pole, a site which offers several unique features for TeV gamma ray astronomy.

Vhe Gamma Rays From Her X-1 in June–July 1985

We have observed Her X-1 for 29 hours during June and July, 1985, with the Haleakala 10 m2 Cherenkov-light gamma-ray telescope, operated at a threshold below 300 GeV. Special attention was given to a search for bursts. We report evidence for possible bursts on days 165 and 168 at orbit phases of.87,.93, and.60 of the binary system.

VHE Gamma Rays from the X-Ray Pulsar 4U0115+63

The x-ray binary pulsar, UHURU designation 4U0115+63, was observed for 39 hours from August through December 1985 at the Haleakala Gamma Observatory. Three intervals of ≤1000 seconds exhibited significant (chance probability ≤ 10-3) pulsation at the characteristic 3.6 second period of the neutron star member of the binary system. The average peak flux above 0.2 TeV for these observations was (2.0 ± 0.4) x 10-9 cm-2 sec-1. These observations are consistent with previous reports of the sporadic nature of this source.

Vhe Gamma Rays from the Crab Pulsar

The Haleakala 10m2 Cherenkov light telescope, which has an estimated energy threshold for gamma-induced atmospheric cascades of 2 x 1011eV, has observed the Crab pulsar, PSR0531, for a total of more than 211 hours. The results of analysis of 10% of this data are reported. Using standard methods of periodic analysis, pulsar periodicity consistent with radio ephemerides has been observed on at least two occasions. The light curve obtained exhibits both a primary and a secondary peak. Like other known astrophysical VHE gamma sources, this pulsar appears episodic in its emissions, with episodes lasting less than an hour.