Volume 627, July 2019
|Number of page(s)||11|
|Published online||12 July 2019|
The large gamma-ray flare of the flat-spectrum radio quasar PKS 0346−27⋆
Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
2 Institut für Theoretische Physik und Astrophysik, Universität Würzburg, Emil-Fischer-Str. 31, 97074 Würzburg, Germany
3 INAF/IAPS, Via Fosso del Cavaliere 100, 00133 Roma, Italy
4 US Naval Research Laboratory, Code 7653, 4555 Overlook Ave. SW, Washington, DC 20375-5352, USA
5 Space Science Data Center – Agenzia Spaziale Italiana, Via del Politecnico, snc, 00133 Roma, Italy
6 Istituto Nazionale di Fisica Nucleare, Sezione di Perugia, 06123 Perugia, Italy
Accepted: 19 June 2019
Aims. In this paper, we characterize the first γ-ray flaring episode of the flat-spectrum radio quasar PKS 0346−27 (z = 0.991), as revealed by Fermi-LAT monitoring data, and the concurrent multi-wavelength variability observed from radio through X-rays.
Methods. We studied the long- and short-term flux and spectral variability from PKS 0346−27 by producing γ-ray light curves with different time binning. We complement the Fermi-LAT data with multi-wavelength observations from the Atacama Large Millimeter Array (radio mm-band), the Rapid Eye Mount telescope (near-infrared) and Swift (optical-UV and X-rays). This quasi-simultaneous multi-wavelength coverage allowed us to construct time-resolved spectral energy distributions (SEDs) of PKS 0346−27 and compare the broadband spectral properties of the source between different activity states using a one-zone leptonic emission model.
Results. PKS 0346−27 entered an elevated γ-ray activity state starting from the beginning of 2018. The high-state continued throughout the year, displaying the highest fluxes in May 2018. We find evidence of short-time scale variability down to approximately 1.5 h, which constrains the γ-ray emission region to be compact. The extended flaring period was characterized by a persistently harder spectrum with respect to the quiescent state, indicating changes in the broadband spectral properties of the source. This was confirmed by the multi-wavelength observations, which show a shift in the position of the two SED peaks by approximately two orders of magnitude in energy and peak flux value. As a result, the non-thermal jet emission completely outshines the thermal contribution from the dust torus and accretion disk during the high state. The broadband SED of PKS 0346−27 transitions from a typical Low-Synchrotron-Peaked (LSP) to the Intermediate-Synchrotron-Peaked (ISP) class, a behavior previously observed in other flaring γ-ray sources. Our one-zone leptonic emission model of the high-state SEDs constrains the γ-ray emission region to have a lower magnetic field, larger radius, and higher maximum electron Lorentz factors with respect to the quiescent SED. Finally, we note that the bright and hard γ-ray spectrum observed during the peak of flaring activity in May 2018 implies that PKS 0346−27 could be a promising target for future ground-based Cherenkov observatories such as the Cherenkov Telescope Array (CTA). The CTA could detect such a flare in the low-energy tail of its energy range during a high state such as the one observed in May 2018.
Key words: galaxies: active / galaxies: jets / quasars: individual: PKS 0346−27 / gamma rays: galaxies
Tables of the measured fluxes are only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (22.214.171.124) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/627/A140
© R. Angioni et al. 2019
Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Open Access funding provided by Max Planck Society.
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