A1 Refereed original research article in a scientific journal
PKS 1954-388: RadioAstron Detection on 80,000 km Baselines and Multiwavelength Observations
Authors: Edwards PG, Kovalev YY, Ojha R, An H, Bignall H, Carpenter B, Hovatta T, Stevens J, Voytsik P, Andrianov AS, Dutka M, Hase H, Horiuchi S, Jauncey DL, Kadler M, Lisakov M, Lovell JEJ, McCallum J, Muller C, Phillips C, Plotz C, Quick J, Reynolds C, Schulz R, Sokolovsky KV, Tzioumis AK, Zuga V, Zuga V
Publisher: CAMBRIDGE UNIV PRESS
Publication year: 2017
Journal: Publications of the Astronomical Society of Australia
Journal name in source: PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF AUSTRALIA
Journal acronym: PUBL ASTRON SOC AUST
Article number: ARTN e021
Volume: 34
Number of pages: 10
ISSN: 1323-3580
eISSN: 1448-6083
DOI: https://doi.org/10.1017/pasa.2017.16
Self-archived copy’s web address: https://arxiv.org/abs/1705.02067
We present results from a multiwavelength study of the blazar PKS 1954-388 at radio, UV, X-ray, and gamma-ray energies. A RadioAstron observation at 1.66 GHz in June 2012 resulted in the detection of interferometric fringes on baselines of 6.2 Earth-diameters. This suggests a source frame brightness temperature of greater than 2 x 10(12) K, well in excess of both equipartition and inverse Compton limits and implying the existence of Doppler boosting in the core. An 8.4-GHz TANAMI VLBI image, made less than a month after the RadioAstron observations, is consistent with a previously reported superluminal motion for a jet component. Flux density monitoring with the Australia Telescope Compact Array confirms previous evidence for long-term variability that increases with observing frequency. A search for more rapid variability revealed no evidence for significant day-scale flux density variation. The ATCA light-curve reveals a strong radio flare beginning in late 2013, which peaks higher, and earlier, at higher frequencies. Comparison with the Fermi gamma-ray light-curve indicates this followed similar to 9 months after the start of a prolonged gamma-ray high-statea radio lag comparable to that seen in other blazars. The multiwavelength data are combined to derive a Spectral Energy Distribution, which is fitted by a one-zone synchrotron-self-Compton (SSC) model with the addition of external Compton (EC) emission.
