Showing papers by "John Reynolds published in 1993"
TL;DR: In this article, high-resolution images of the supernova remnant at a frequency of 8.8 GHz were presented, which reveal a spherical shell-like structure with a radius of 0.6 arcsec (4 × 1017 cm, assuming a distance of 50 kpc) and an additional component that is aligned with the optical ring.
Abstract: SUPERNOVA 1987A in the Large Magellanic Cloud, the closest known supernova for 400 years, offers unprecedented opportunities for the detailed study of the evolution of a supernova at all wavelengths. The radio remnant of SN1987A was detected in July 1990 (ref. 1), since when it has steadily brightened at all radio frequencies2. Its present brightness and size are now sufficient for its structure to be resolved. Here, we present high-resolution images of the remnant at a frequency of 8.8 GHz, which reveal a spherical, shell-like structure with a radius of 0.6 arcsec (4 × 1017 cm, assuming a distance of 50 kpc) and an additional component that is aligned with the optical ring (of somewhat larger radius) imaged by the Hubble Space Telescope3. We suggest that this alignment arises from an interaction between the expanding shock wave and dense clouds sheared from the ring. The mean expansion velocity of the supernova shock front, as measured from its current radio size, is ∼30,000 km s−1. Observations made over 600 days suggest, however, that either the remnant is rapidly changing shape or that the expansion velocity is decreasing more rapidly than expected.
49 citations
TL;DR: In this article, the Parkes catalogue was used to measure the 2.3 GHz total and correlated flux densities on a baseline of 275 km of all sources in all sources which are south of declination +10°, have a catalogued 2.7 GHz total flux density exceeding 0.5 Jy, and have a 2.0 GHz spectral index flatter than −0.5.
Abstract: We have measured the 2.3 GHz total and correlated flux densities on a baseline of 275 km of all sources in the Parkes catalogue which (i) are south of declination +10°, (ii) have a catalogued 2.7 GHz total flux density exceeding 0.5 Jy, and (iii) have a 2.7/5.0 GHz spectral index flatter than −0.5. More than 14% of the sample showed visibility amplitudes greater than 0.9, and more than 72% showed visibility amplitudes greater than 0.5. Of the sources with optical or other identifications 79% were quasars. In this paper we briefly summarise the results of this survey.
16 citations
TL;DR: In this article, the authors observed 1 10 -1 01 (18.3 GHz) transition of ortho-cyclopropenylidene, C 3 H 2, at 24 positions in the unusual dense cloud G1.
Abstract: We have observed 1 10 -1 01 (18.3 GHz) transition of ortho-cyclopropenylidene, C 3 H 2 , at 24 positions in the unusual dense cloud G1.6-0.025. Except for one position, the transition is refrigerated, a phenomenon which has not been seen in this transition before and was not predicted to occur. In general, the absorption correlates with the absorption seen in the 2 0 -3 −1 (12.2 GHz) transition of methanol, but there are significant differences. We suspect that collisional excitation at relatively high kinetic temperature (50 K) enhanced by photon trapping is responsible for the refrigeration
8 citations
6 citations