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PKS 1954-388: RadioAstron detection on 80,000 km baselines and multiwavelength observations

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 ORCID: 0000-0001-5273-9817, McCallum, J ORCID: 0000-0002-0233-6937, Mueller, C, Phillips, C, Plotz, C, Quick, J, Reynolds, C, Schulz, R, Sokolovsky, KV, Tzioumis, AK and Zuga, V 2017 , 'PKS 1954-388: RadioAstron detection on 80,000 km baselines and multiwavelength observations' , Publications of the Astronomical Society of Australia, vol. 34 , pp. 1-10 , doi: 10.1017/pasa.2017.16.

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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 × 1012 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 ∼9 months after the start of a prolonged gamma-ray high-state—a 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.

Item Type: Article
Authors/Creators:Edwards, PG and Kovalev, YY and Ojha, R and An, H and Bignall, H and Carpenter, B and Hovatta, T and Stevens, J and Voytsik, P and Andrianov, AS and Dutka, M and Hase, H and Horiuchi, S and Jauncey, DL and Kadler, M and Lisakov, M and Lovell, JEJ and McCallum, J and Mueller, C and Phillips, C and Plotz, C and Quick, J and Reynolds, C and Schulz, R and Sokolovsky, KV and Tzioumis, AK and Zuga, V
Keywords: galaxies: active, galaxies: jets, gamma rays: galaxies, ISM: structure, radio continuum: galaxies
Journal or Publication Title: Publications of the Astronomical Society of Australia
Publisher: C S I R O Publishing
ISSN: 1323-3580
DOI / ID Number: 10.1017/pasa.2017.16
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© Astronomical Society of Australia 2017

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