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H.E.S.S. Monitoring of PKS 2155-304 in 2015 and 2016

Institute of Nuclear Physics, Polish Academy of Sciences, PL-31342 Krakow, Poland
Institut für Theoretische Physik, Lehrstuhl IV: Weltraum und Astrophysik, Ruhr-Universität Bochum, D-44780 Bochum, Germany
Centre for Space Science, North-West University, Potchefstroom 2520, South Africa
Landessternwarte, Universität Heidelberg, Königstuhl, D-69117 Heidelberg, Germany
Author to whom correspondence should be addressed.
Galaxies 2019, 7(1), 21;
Received: 24 November 2018 / Revised: 3 January 2019 / Accepted: 14 January 2019 / Published: 19 January 2019
(This article belongs to the Special Issue Monitoring the Non-Thermal Universe)
PDF [473 KB, uploaded 29 January 2019]


PKS 2155-304 is one of the brightest blazar located in Southern Hemisphere, monitored with H.E.S.S. since the first light of the experiment. Here we report multiwavelength monitoring observations collected during the period of 2015–2016 with H.E.S.S., Fermi-LAT, Swift-XRT, Swift-UVOT, and ATOM. Two years of multiwavelength data with very good temporal coverage allowed to characterize broadband emission observed from the region of PKS 2155-304 and study potential multifrequency correlations. During the period of monitoring, PKS 2155-304 revealed complex multiwavelength variability with two outbursts characterized by completely different multiband properties. The 2015 activity of the blazar is characterized by a flare observed at all wavelengths studied. The broadband emission observed during the outburst is well correlated without any time lags. Contrary to 2015, in 2016, only orphan outburst in the optical and ultraviolet wavelengths was observed. Such an orphan activity is reported for the first time for the blazar PKS 2155-304. View Full-Text
Keywords: active galactic nuclei; blazar variability; multi-wavelength active galactic nuclei; blazar variability; multi-wavelength

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Wierzcholska, A.; Zacharias, M.; Jankowsky, F.; Wagner, S. H.E.S.S. Monitoring of PKS 2155-304 in 2015 and 2016. Galaxies 2019, 7, 21.

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