| 22nd of June 2022 |
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| Rapid Intra-Day Variability in PMN J1726+0639 |
| by Bignall et al. |
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Bignall et al. report the discovery of rapid intra-day variability in
the radio source PMN J1726+0639 at GHz frequencies, during a survey to
search for such variability with the Australia Telescope Compact
Array. Follow-up observations were conducted over two years and
revealed a clear, repeating annual cycle in the rate, or
characteristic timescale, of variability, showing that the observed
variations can be attributed to scintillations from interstellar
plasma inhomogeneities (analogous to the twinkling of starlight).
The authors fit kinematic
models to the data, allowing for finite anisotropy in the
scintillation pattern.
The parameters are inconsistent
with expectations from a previously proposed model of scattering
associated with plasma filaments radially oriented around hot
stars. We note that evidence for a foreground interstellar cloud
causing anomalous Ca II absorption towards the nearby star Rasalhague
(alpha Oph) has been previously reported, and Bignall et al. speculate that the
interstellar scintillation of PMN J1726+0639 might be associated with
this nearby cloud.
The image above shows light curves for PMN J1726+0639 during an epoch of rapid scintillation, at frequencies between 4500 MHz and 10600 MHz, averaged over ∼100 MHz intervals and 150-second time intervals. The lowest frequencies are in red, and the highest are shown in violet. The rapid intra-day variability in flux density is clear. |