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29th of September 2020
Optical study of an intra-hour variable radio source
by Madrid et al.
Intra-day variability (IDV) of radio quasars was recognized in the 1980s, and became a topic of intense interest a decade later with the discovery of intra-hour variations (IHVs). The combination of large amplitude and short timescale strongly favoured scintillation, due to strongly scattering plasma clouds in the solar neighborhood, as the cause.

Observations with the Australia Telescope Compact Array revealed intra-hour variations in the radio source PKS B1322-110. As part of an optical follow-up, Madrid et al. obtained Gemini Hα and Hα continuum (HαC) images of the PKS B1322-110 field. A strong detection of PKS B1322-110 in the Hα−HαC image prompted the first optical spectrum of PKS B1322-110, revealing that PKS B1322-110 is a flat-spectrum radio quasar at a redshift of z=3.007. The figure above shows the GMOS spectrum of PKS B1322-110, displayed at the observed wavelength. The shift in wavelength from the rest-frame values allows the redshift to be measured. The letter T denotes prominent telluric absorption lines (due to the Earth's atmosphere) that are present at wavelengths larger than 6700 angstroms. At a redshift of z=3.007, PKS B1322-110 is at the high end of the redshift distribution of scintillating radio sources, with a previous study indicating that radio sources that show interstellar scintillation drop steeply beyond redshift ∼2. The paper was recently published in the Astrophysical Journal.

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