The discovery of a twinkling radio source with Apertif: Extreme scintillation from turbulent plasma in the direct solar neighbourhood

Propagation through turbulent interstellar plasma leads to interstellar scintillation of very compact radio sources. Such scintillations are a unique probe of the sub-AU scale structure of the interstellar medium, as well as of the micro-arcsecond structure of radio sources. Scintillations of a few percent on timescales of a few days is commonly seen at centimetre wavelengths and is thought to result from the line-of-sight integrated turbulence in Milky Way's interstellar plasma. Only three sources so far have shown more extreme variations (larger than tens of per-cent) on shorter timescales (hours or less). Such extreme variations requires propagation through very nearby (d < 10 pc) anomalously dense (n~10^2 cm^-3) plasma clouds. We report the discovery and monitoring, using Apertif, of a unique radio source showing extreme intra-hour variations at 1.4 GHz, with flux changes up to a factor 4 within 15 minutes. The longer wavelength of the observed scintillations, combined with the short timescales, requires scattering in a dense plasma that is extremely close: 1-2 lightyear, a distance which is within the Sun's sphere of gravitational influence.

Our results show the promise of deep large-area surveys done with radio telescopes with a large field of view of uncovering more of these interesting sources that are a unique probe to explore the plasma in the direct solar neighbourhood.