Showing papers by "Mike Irwin published in 1989"
TL;DR: In this article, photometric data were presented for the gravitationally lensed quasar system 2237 + 0305, which showed unambiguous evidence for a change in brightness of one of the four component images.
Abstract: New photometric data are presented for the gravitationally lensed quasar system 2237 + 0305, which shows unambiguous evidence for a change in brightness of one of the four component images. This represents the first detection of a microlensing event. For the case where the source intersects the critical curve of the microlens, observational constraints on the timescale for the event allows a limit of 0.1 solar mass or less to be placed on the mass on the lensing object. The data illustrate the immense potential for obtaining information on the size of the quasar-continuum-emitting region, together with the mass function of compact objects in the lensing galaxy, through a comprehensive photometric monitoring program of the 2237 + 0305 system. 13 refs.
249 citations
TL;DR: In this article, the authors reported new interferometric observations of AS431 using MERLIN (the Jodrell Multi-Element Radio Linked Interferometer Network), in which the sensitivity was sufficient to map the stellar thermal-continuum radio emission with a beam size of 0.6 arcsec, corresponding to a spatial separation of 1,100 AU at the assumed distance of 1.9 kpc.
Abstract: THE Wolf–Rayet star AS431 (number 147 in ref. 1) is known to be bright at X-ray and radio wavelengths2,3, and previous radio-interferometric observations indicate that it has an extended struc-ture3. Here we report new interferometric observations of AS431 using MERLIN (the Jodrell Multi-Element Radio Linked Inter-ferometer Network), in which the sensitivity was sufficient to map the stellar thermal-continuum radio emission with a beam size of 0.1 arcsec. The object is resolved into two radio sources, separated by 0.6 arcsec, corresponding to a spatial separation of 1,100 AU at the assumed distance of 1.9 kpc. The computed brightness of the two sources, ∼10,000 K, is typical of optically thick thermal emission from a stellar wind, but compared with other observations2suggests that some part of the emission is non-thermal. One of the radio components corresponds to the position of the single source revealed by accurate optical observations. We simulate the observed total radio spectrum with a two-component model for the emission.
49 citations
TL;DR: The Q1429-008 system comprises two components, R-band magnitudes m(R) = 17.7 and 20.8, and the velocity difference between the two spectra, derived from cross-correlation techniques, is 260 + or - 300 km/s as mentioned in this paper.
Abstract: Observational evidence is presented for the existence of a new wide-separation, high-redshift gravitationally lensed quasar Q1429-008. The Q1429-008 system comprises two components, R-band magnitudes m(R) = 17.7 and 20.8. The spectra of the two components are very similar although small systematic differences in the emission-line strengths are probably present. The velocity difference between the two spectra, derived from cross-correlation techniques, is 260 + or - 300 km/s. The observational data are consistent with a deflector of cluster mass and dimensions, at a redshift about 1.5, but such an observer-deflector-source geometry is unlikely a priori. If the deflector is at the 'most likely' redshift, about 0.6, then the lower limit to the deflector mass-to-light ratio is extremely high. 17 refs.
25 citations