The flat-spectrum radio quasar 3C 345 from the high to the low emission state

¹ Dipartimento di Fisica e Astronomia “G. Galilei”, Università di Padova, Vicolo dell’Osservatorio 3, 35122 Padova, Italy
e-mail: marco.berton@unipd.it
² INAF – Osservatorio Astronomico di Brera, via E. Bianchi 46, 23807 Merate (LC), Italy
³ Purple Mountain Observatory, Chinese Academy of Sciences, 2 West Beijing Road, Nanjing 210008, PR China
⁴ Aalto University Metsähovi Radio Observatory, Metsähovintie 114, 02540 Kylmälä, Finland
⁵ Aalto University Department of Radio Science and Engineering, 00076 Aalto, Finland
⁶ Universidad de Concepción, Departamento de Astronomía, Casilla 160-C, Concepción, Chile
⁷ Yunnan Observatories, Chinese Academy of Sciences, Kunming, Yunnan 650011, PR China
⁸ School of Physics, Huazhong University of Science and Technology, Wuhan 430074, PR China
⁹ Nordic Optical Telescope, Apartado 474, 38700 Santa Cruz de La Palma, Spain
¹⁰ Osservatorio Astronomico della Regione Autonoma Valle d’Aosta, Saint Barthelemy, 11020 Nus, Italy

Received: 21 July 2017
Accepted: 7 March 2018

Abstract

We report simultaneous observations at different energy bands in radio, optical, UV, X-rays and γ rays of the flat-spectrum radio-quasar 3C 345. We built the light curve of the source at different frequencies from 2008, the beginning of the Fermi all-sky survey, to 2016, using new data and public archives. In particular we obtained several optical spectra, to study the behavior of emission lines and the continuum in different activity states and to derive the black hole mass. 3C 345 showed two flaring episodes in 2009, which occurred simultaneously in γ ray, optical/UV and X-rays, and were later followed in radio. The source shows an inverse Compton dominated spectral energy distribution, which moved from higher to lower frequencies from the high to the low state. The reverberation of emission lines during one outburst event allowed us to constrain the location of production of γ rays very close to the broad-line region, and possibly in the jet-base. We report the observation of an increased accretion after the outburst, possibly induced by the decrease of magnetic field intensity with respect to the low state.