Radio Ridge Research Articles

Observations of the Supernova Remnant IC443 at 1{middle dot}42 GHz

The supernova remnant IC443 has been mapped at 1·42 GHz with a resolution of |${1}^{\prime}\cdot05\times{2}^{\prime}\cdot71$| arc, using the Half-Mile telescope at Cambridge. The map shows that the source has a thick shell extending over the eastern half of its circumference with no evidence of a shell on the western edge. There is remarkably detailed agreement of optical and radio features, with some optical filaments clearly located on the outer edge of radio ridges. Comparison of the map with other high resolution maps at higher frequencies shows an increase in the spectral index near the brightest optical features. Estimates of some physical parameters of the source are derived in the final section of the paper.

Soft X-ray Emission from Galactic Radio Spurs

Shklovsky and Sheffer1 have recently raised the interesting possibility that the galactic radio spurs could be soft X-ray sources. As radio spurs have often been considered to be very old supernova remnants2,3, and since three old remnants have been found to be soft X-ray sources4,5, this idea has particular merit. Shklovsky and Sheffer point out that the soft X-ray (0.21 to 0.28 keV) map of Bowyer et al.6 shows enhanced emission in the northern galactic hemisphere in a region coincident with secondary radio ridges of the North Polar Spur7 and that this correlation may provide experimental verification of the hypothesis concerning the possible supernova remnant origin of the spurs.

Filamentary Nebulosity in the Vicinity of Loop III

PROJECTING from the plane of the galaxy are three loops of nonthermal radio emission. Loop I, originally called the North Polar Spur, is 113° in diameter1 and is centred on lII = 330°; bII = 19.5°. The Cetus Arc, now called Loop II, is 92° in diameter2 and is centred at lII = 100; bII = −30°. Loop III is 71° in diameter3 and is centred near the north celestial pole at lII = 124°; bII = 11.5°. It was proposed in ref. 1 that Loop I is the remnant of a supernova close to the Sun, as the radio emission is non-thermal and seems to come from a shell source. If the radio loops are supernova remnants, then we would expect to observe filamentary nebulosity surrounding their radio ridges, as is observed in well known supernova remnants such as the Cygnus Loop.