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A search for variable radio emission in the galactic plane Taylor, Andrew Russell


A description and the results of two surveys to search for highly variable radio emission in the galactic plane are presented. The surveys were carried out by making daily beamswitched maps of the survey regions and comparing the results of each day to the average of all days for evidence of variability. The first survey, at 21 cm, maps an area of 86 sq. deg. of the local spiral arm, in the direction of the constellation Cygnus, and searches for variability to a sensitivity of ~ 0.3 Jy. The second survey, at 6 cm, covers an area of 56 sq. deg. in the galactic longitude range (ℓˡˡ) 40°- 140°. The study of variability in this survey is not yet complete but variations at a level of ~10 mJy are expected to be measurable. It is concluded that large intensity variations (greater than ~ 1 Jy) on a time scale of days are extremely rare; only one possible variation at a level of 0.9 Jy was detected during the 52 days of the 21 cm survey. A preliminary examination of the 6 cm data reveals one highly variable radio source, designated GT 0236+610, that reached a maximum flux density of 285 mJy. The results of further observations of this source are presented. The 6 cm observations were averaged over the complete survey period and the data were searched for compact sources down to a level of 10 - 20 mJy. The positions and 6 cm flux density for the resulting 196 compact sources are listed.

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