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4th of July 2017
A radio outburst from PKS 1954-388
by Phil Edwards (CASS)
PKS 1954-388 is an active galaxy about 6 billion light years from our own Galaxy (at a redshift of 0.63). It is regularly observed with the ATCA as part of part of a multi-frequency program monitoring galaxies observed with NASA's Fermi gamma-ray satellite. Observations are made every month or two in the 5.5, 9, 17 and 38 GHz bands in order to study the variability at radio wavelengths and to search for correlations with gamma-ray activity. As PKS 1954-388 is a bright radio source, the ATCA observations can be made in "snap-shot" mode, with observations of several minutes sufficient to measure the flux density of the source. A portion of the resulting light-curve is shown above, providing a text-book example of the evolution of a radio flare. The radio emission from active galaxies is synchrotron radiation, produced by relativistic electrons under the influence of a magnetic field. A radio outburst can be generated by an increase in the number of high energy electrons, which produce higher frequency radio emission, and as they lose energy gradually produce more emission at lower frequencies. The plot above shows the outburst peaks first at 38 and 17 GHz, then later at 9 GHz, and later again at 5.5 GHz. It is notable that the peaks are also sharper, and stronger, at the higher frequencies, in line with expectations.

The data are presented as part of a multi-wavelength study of this source in the paper "PKS 1954-388: RadioAstron Detection on 80,000 km Baselines and Multiwavelength Observations" by Edwards et al., published in the Publications of the Astronomical Society of Australia.

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