Walter K. Gear

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SCUBA, the Submillimetre Common-User Bolometer Array, built by the Royal Observatory Edinburgh for the James Clerk Maxwell Telescope, is the most versatile and powerful of a new generation of submillimetre cameras. It combines a sensitive dual-waveband imaging array with a three-band photometer, and is sky-background limited by the emission from the Mauna(More)
We present total and polarized intensity images of 15 active galactic nuclei obtained with the Very Long Baseline Array at 7 mm wavelength at 17 epochs from 1998 March to 2001 April. At some epochs the images are accompanied by nearly simultaneous polarization measurements at 3 mm, 1.35/0.85 mm, and optical wavelengths. Here we analyze the 7 mm images to(More)
Dust emission around the nearby star ǫ Eridani has been imaged using a new submillimetre camera (SCUBA at the JCMT). At 850 µm wavelength a ring of dust is seen, peaking at 60 AU from the star and with much lower emission inside 30 AU. The mass of the ring is at least ∼ 0.01 M ⊕ in dust, while an upper limit of 0.4 M ⊕ in molecular gas is imposed by CO(More)
Of the blazars detected by EGRET in GeV c-rays, 3C 279 is not only the best observed by EGRET but also one of the best monitored at lower frequencies. We have assembled 11 spectra, from GHz radio through GeV c-rays, from the time intervals of EGRET observations. Although some of the data have appeared in previous publications, most are new, including data(More)
Blazars are the most extreme active galactic nuclei. They possess oppositely directed plasma jets emanating at near light speeds from accreting supermassive black holes. According to theoretical models, such jets are propelled by magnetic fields twisted by differential rotation of the black hole's accretion disk or inertial-frame-dragging ergosphere. The(More)
In the local Universe, most galaxies are dominated by stars, with less than ten per cent of their visible mass in the form of gas. Determining when most of these stars formed is one of the central issues of observational cosmology. Optical and ultraviolet observations of high-redshift galaxies (particularly those in the Hubble Deep Field) have been(More)
Modern far-infrared and submillimeter instruments require large-format arrays. We consider the relative performance of filled-array (bare pixel) and feedhorn-coupled architectures for bolometer focal planes. Based on typical array parameters, we quantify the relative observing speeds and comment on the merits of the different architectures. Filled arrays(More)
The blazar 3C 279, one of the brightest identified extragalactic objects in the γ-ray sky, underwent a large (factor of ∼10 in amplitude) flare in γ-rays towards the end of a 3-week pointing by CGRO, in 1996 January-February. The flare peak represents the highest γ-ray intensity ever recorded for this object. During the high state, extremely rapid γ-ray(More)
We report on multi-frequency linear polarization monitoring of 15 active galactic nuclei containing highly relativistic jets with apparent speeds from ∼4 c to >40c. The measurements were obtained at optical, 1 mm, and 3 mm wavelengths , and at 7 mm with the Very Long Baseline Array. The data show a wide – 2 – range in degree of linear polarization among the(More)