Speaker
Description
Determining the origins of low-frequency (~MHz) variability of extragalactic sources has, until recently, largely been limited to small populations and/or single frequencies. Variability offers a unique opportunity to study both intrinsic properties of sources as well as the intervening media between source and observer. However, large population studies with significant spectral and temporal coverage have only recently become available with the development of radio telescopes like the Murchison Widefield Array (MWA). Using two epochs of the Galactic and Extragalactic All-sky MWA (GLEAM) survey, we have conducted a variability analysis of over 23,000 sources across 100—231MHz over a year-long timescale, the only spectral variability study of its kind. Contrary to expectations, we find a large sub-population of radio galaxies exhibiting large variation in flux density and spectral shape which cannot be explained entirely by either intrinsic or extrinsic mechanisms. Intrinsic origins, such as flaring active galactic nuclei (AGN), suggest a significant component of the flux density comes from the core/jet or evolution of these sources within one year. Extrinsic variability, such as refractive interstellar scintillation, suggests unexpected morphologies, like hot-spots or knots in the lobes of radio galaxies, contradictory to what we expect at low frequencies. Our measured variations suggest that low-frequency variability is more common than previously thought, and highlight the insufficient understanding of the emission mechanisms at low frequencies, and AGN evolutionary scenarios. In the SKA era, as large-scale, spectral variability surveys become achievable, rigorous statistics and understanding of the origins of low-frequency variability is needed. This study provides the first standardised methodology for future statistical analyses and classifications of low-frequency spectral variability.
| Suggested presentation duration (minutes) | 15 min. |
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