2025MNRAS.536.1344S

We present multifrequency radio data for a sample of Narrow-Line type 1 Seyfert (NLS1) galaxies. We first focus on the sub-class of gamma-ray emitting NLS1 galaxies, studying the long-term radio variability of five sources and comparing it to their gamma-ray state. We then extend the observations of the southern NLS1 galaxy sample of Chen et al. by observing several candidate NLS1 sources for the first time, and re-observing several other gamma-ray-quiet sources to obtain a first indication of their radio variability. We find that the gamma-ray emitting NLS1 galaxies are highly variable radio emitters and that there are instances of contemporaneous flaring activity between the radio and gamma-ray bands (PKS 0440$-$00, PMN J0948+0022, and PKS 1244$-$255). However, there are also cases of significant radio outbursts without gamma-ray counterparts (PMN J0948+0022 and PKS 2004$-$447). The five gamma-ray NLS1s favour flat or inverted radio spectra, although the spectral indices vary significantly over time. For the gamma-ray-quiet sample, the difference between the previous observations at 5.5 GHz and new Australia Telescope Compact Array (ATCA) observations indicates that over half of the 14 sources exhibit apparent variability. In contrast to gamma-ray-loud sources, gamma-ray-quiet objects tend to have steep spectra, especially in the lower radio band (887.5-1367.5 MHz) of Australian Square Kilometre Array Pathfinder (ASKAP) data, with a number of the variable sources having flatter spectra at higher radio frequencies.