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Published December 2016 | Published + Submitted
Journal Article Open

The awakening of the γ-ray narrow-line Seyfert 1 galaxy PKS 1502+036


After a long low-activity period, a γ-ray flare from the narrow-line Seyfert 1 PKS 1502+036 (z = 0.4089) was detected by the Large Area Telescope (LAT) on board Fermi in 2015. On 2015 December 20, the source reached a daily peak flux, in the 0.1–300 GeV band, of (93 ± 19) × 10^(−8) ph cm^(−2) s^(−1), attaining a flux of (237 ± 71) × 10^(−8) ph cm^(−2) s^(−1) on 3-h time-scales, which corresponds to an isotropic luminosity of (7.3 ± 2.1) × 10^(47) erg s^(−1). The γ-ray flare was not accompanied by significant spectral changes. We report on multiwavelength radio-to-γ-ray observations of PKS 1502+036 during 2008 August–2016 March by Fermi-LAT, Swift, XMM–Newton, Catalina Real-Time Transient Survey and the Owens Valley Radio Observatory (OVRO). An increase in activity was observed on 2015 December 22 by Swift in optical, UV and X-rays. The OVRO 15 GHz light curve reached the highest flux density observed from this source on 2016 January 12, indicating a delay of about three weeks between the γ-ray and 15 GHz emission peaks. This suggests that the γ-ray-emitting region is located beyond the broad-line region. We compared the spectral energy distribution (SED) of an average activity state with that of the flaring state. The two SED, with the high-energy bump modelled as an external Compton component with seed photons from a dust torus, could be fitted by changing the electron distribution parameters as well as the magnetic field. The fit of the disc emission during the average state constrains the black hole mass to values lower than 10^8 M_⊙. The SED, high-energy emission mechanisms and γ-ray properties of the source resemble those of a flat spectrum radio quasar.

Additional Information

© 2016 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. Accepted 2016 September 13. Received 2016 September 12; in original form 2016 June 22. Published: 14 September 2016. The Fermi LAT Collaboration acknowledges generous ongoing support from a number of agencies and institutes that have supported both the development and the operation of the LAT as well as scientific data analysis. These include the National Aeronautics and Space Administration and the Department of Energy in the United States, the Commissariat à l'Energie Atomique and the Centre National de la Recherche Scientifique/Institut National de Physique Nucléaire et de Physique des Particules in France, the Agenzia Spaziale Italiana and the Istituto Nazionale di Fisica Nucleare in Italy, the Ministry of Education, Culture, Sports, Science and Technology (MEXT), High Energy Accelerator Research Organization (KEK) and Japan Aerospace Exploration Agency (JAXA) in Japan, and the K. A. Wallenberg Foundation, the Swedish Research Council and the Swedish National Space Board in Sweden. Additional support for science analysis during the operations phase is gratefully acknowledged from the Istituto Nazionale di Astrofisica in Italy and the Centre National d'Études Spatiales in France. We thank the Swift team for making these observations possible, the duty scientists, and science planners. The OVRO 40 m monitoring programme is supported in part by NASA grants NNX08AW31G and NNX11A043G, and NSF grants AST-0808050 and AST-1109911. The CSS survey is funded by the National Aeronautics and Space Administration under Grant No. NNG05GF22G issued through the Science Mission Directorate Near-Earth Objects Observations Programme. The CRTS survey is supported by the US National Science Foundation under grants AST-0909182. Based on observations obtained with XMM–Newton, an ESA science mission with instruments and contributions directly funded by ESA Member States and NASA. Part of this work was done with the contribution of the Italian Ministry of Foreign Affairs and Research for the collaboration project between Italy and Japan. We thank S. Ciprini, J. Perkins, and the anonymous referee for useful comments and suggestions.

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August 19, 2023
October 25, 2023