| 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.
|
