arXiv subjects

E. I. Robson

Publications and source records attributed to E. I. Robson.

24 records · Page 2Linked to original sources

arXiv1999

SCUBA Observations of the Elliptical Galaxy NGC 4374

We present SCUBA imaging and photometry of the elliptical galaxy NGC 4374. The imaging observations are used to examine the spatial distribution of thermal emission from dust and the radio to infrared continuum spectrum. In the SCUBA 850 um image, the galaxy is found to be a point source, constraining the emission to less than 15'' (1.5 kpc for a distance of 20.74 Mpc). The simplest interpretation is that the 2000 um to 850 um SCUBA emission is synchroton from a compact core or inner-jet, and most unlikely thermal emission from cold diffuse dust. We cannot exclude free-free emission, but this would be very unexpected. The thermal emission from dust is shown in IRAS data and these along with the 450 um SCUBA datum give a dust temperature of 35 K, corresponding to a dust mass of 0.12 million solar masses. These are pilot observations in a program to look for cold, diffusely distributed dust in elliptical galaxies, however much deeper 450 um imaging is required to investigate this in NGC 4374.

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arXiv1998

Millimetre and submillimetre continuum observations of the core and hotspots of Cygnus-A

We present millimetre photometry and submillimetre imaging of the central core and two hotspots in the radio lobes of the galaxy Cygnus-A. For both hotspots and the central core the synchrotron spectrum continues smoothly from the radio to a frequency of 677 GHz. The spectral index of the hotspots is constant over our frequ ency range, with a spectral index of about -1.0, which is steeper than at lower frequencies and represents the emission from an aged population of electrons. The core is significantly flatter, with a spectral index of -0.6 +/- 0.1, suggestive of an injected spectrum with no ageing, but some evidence for steepening exists at our highest observing frequency. Although IRAS data suggest t he presence of dust in Cygnus-A, our 450 um data show no evidence of cold dust, therefore the dust component must have a temperature lying between 85 K and 37 K, respectively.

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arXiv1998

SCUBA: A common-user submillimetre camera operating on the James Clerk Maxwell Telescope

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 Kea atmosphere at all observing wavelengths from 350 microns to 2 mm. The increased sensitivity and array size mean that SCUBA maps close to 10,000 times faster than its single-pixel predecessor (UKT14). SCUBA is a facility instrument, open to the world community of users, and is provided with a high level of user support. We give an overview of the instrument, describe the observing modes and user interface, performance figures on the telescope, and present a sample of the exciting new results that have revolutionised submillimetre astronomy.

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arXiv1998

SCUBA - A submillimetre camera operating on the James Clerk Maxwell Telescope

The Submillimetre Common-User Bolometer Array (SCUBA) is one of a new generation of cameras designed to operate in the submillimetre waveband. The instrument has a wide wavelength range covering all the atmospheric transmission windows between 300 and 2000 microns. In the heart of the instrument are two arrays of bolometers optimised for the short (350/450 microns) and long (750/850 microns) wavelength ends of the submillimetre spectrum. The two arrays can be used simultaneously, giving a unique dual-wavelength capability, and have a 2.3 arc-minute field of view on the sky. Background-limited performance is achieved by cooling the arrays to below 100 mK. SCUBA has now been in active service for over a year, and has already made substantial breakthroughs in many areas of astronomy. In this paper we present an overview of the performance of SCUBA during the commissioning phase on the James Clerk Maxwell Telescope (JCMT).

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arXiv1998

30 years of multi-wavelength observations of 3C 273

We present a wide multi-wavelength database of most observations of the quasar 3C 273 obtained during the last 30 years. This database is the most complete set of observations available for an active galactic nucleus (AGN). It contains nearly 20'000 observations grouped together into 70 light curves covering 16 orders of magnitude in frequency from the radio to the gamma-ray domain. The database is constituted of many previously unpublished observations and of most publicly available data gathered in the literature and on the World Wide Web (WWW). It is complete to the best of our knowledge, except in the optical (UBV) domain where we chose not to add all observations from the literature. In addition to the photometric data, we present the spectra of 3C 273 obtained by the International Ultraviolet Explorer (IUE) satellite. In the X-ray domain, we used the spectral fit parameters from the literature to construct the light curves. Apart from describing the data, we show the most representative light curves and the average spectrum of 3C 273. The database is available on the WWW in a homogeneous and clear form and we wish to update it regularly by adding new observations.

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arXiv1994

Modelling the millimetre-infrared flaring behaviour of the quasar 1253-055 (3C 279)

The infrared through millimetre light curve of 3C 279 is investigated for the period of 1986 until mid-1994, during which time several flares were observed. A quiescent spectrum (identified with emission from an underlying jet) is presented. Both the near-IR and 375-150 GHz regimes are shown to be well described by power laws, with no evidence for any thermal contribution in the IR. Successful isolation of the flaring component by subtraction of a base level is found to be difficult. Dividing each individual flare into two regimes corresponding to before and after maximum flux, we find strong linear correlations between log 90 GHz flux and 22-90 GHz spectral slope. Furthermore, the gradient of the linear correlation steepens as the flare decays after maximum. This trend is observed for several successive flares, and can be successfully explained in terms of evolution of the flare according to the the shocked-jet model of Marscher & Gear (1985).

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