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9th of March 2015
The Spectral Variability of the GHz-Peaked Spectrum Radio Source PKS 1718-649 and a Comparison of Absorption Models
by Steven Tingay (Curtin University)
The figure shows data collected from the Australia Telescope Compact Array (ATCA) using the Compact Array Broadband Backend (green, grey, and blue data points), covering the full frequency range from 1 to 10 GHz, for PKS 1718-649 (NGC 6328), a compact GHz-Peaked radio source ( Tingay et al. 2015). The CABB measurements were obtained in three different observing sessions, over approximately 18 months. Variability is clearly seen both below the spectral peak and above. This variability is best explained by variations in the free-free absorption due to intervening ionised gas in NGC 6328 (explains variability below the peak) and variations in the intrinsic synchrotron spectrum (explains variability above the peak). The solid lines show various theoretical models. Models for homogenous absorption fail (purple and brown solid lines) and models for inhomogenous absorption succeed (blue, green, and grey solid lines), when additional data at approximately 700 MHz and 150 MHz are included from the Parkes 64-m Dish and the Murchison Widefield Array (MWA), respectively. The Parkes and MWA data are shown as red bars in the figure.

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