Restarting activity in the nucleus of PBC J2333.9-2343

An extreme case of jet realignment

¹ INAF–Istituto di Astrofisica e Planetologia Spaziali di Roma (IAPS-INAF), via del Fosso del Cavaliere 100, 00133 Roma, Italy
e-mail: lorena.hernandez@iaps.inaf.it
² Istituto di Astrofisica Spaziale e Fisica Cosmica (IASF-INAF), via P. Gobetti 101, 40129 Bologna, Italy
³ INAF–Osservatorio Astronomico di Brera, via E. Bianchi 46, 23807 Merate, Italy
⁴ Departamento de Ciencias Físicas, Universidad Andrés Bello, Fernández Concha 700, Las Condes, Santiago, Chile
⁵ Ethiopian Space Science and Technology Institute (ESSTI), Entoto Observatory and Research Center (EORC), Astronomy and Astrophysics Research Division, PO Box 33679, Addis Ababa, Ethiopia
⁶ Instituto de Astrofísica de Andalucía, CSIC, Glorieta de la Astronomía, s/n, 18008 Granada, Spain
⁷ Instituto Nacional de Astrofísica, Óptica y Electrónica, Apartado Postal 51-216, 72000 Puebla, Mexico

Received: 30 January 2017
Accepted: 24 April 2017

Abstract

Context. The giant radio galaxy PBC J2333.9-2343 shows different characteristics at different wavebands that are difficult to explain within the actual generic schemes of unification of active galactic nuclei (AGN). It is therefore a good candidate host for different phases of nuclear activity.

Aims. We aim at disentangling the nature of this AGN by using simultaneous multiwavelength data.

Methods. We obtained data in 2015 from the Very Long Baseline Array (VLBA), the San Pedro Mártir telescope, and the XMM-Newton observatories. This allows the study of the nuclear parts of the galaxy through its morphology and spectra and the analysis of the spectral energy distribution (SED). We also reanalysed previously-presented optical data from the San Pedro Mártir telescope from 2009 to provide a homogeneous comparison.

Results. At X-ray frequencies the source is unabsorbed. The optical spectra are of a type 1.9 AGN, both in 2009 and 2015, although showing a broader component in 2015. The VLBA radio images show an inverted spectrum with a self-absorbed, optically thick compact core (α_c = 0.40, where S_ν ∝ ν^{+ α}) and a steep-spectrum, optically thin jet (α_j,8−15 = −0.5). The SED resembles that of typical blazars and is best represented by an external Compton (EC) model with a viewing angle of approximately 3–6°. The apparent size of the large-scale structure of PBC J2333.9-2343 must correspond to an intrinsic deprojected value of approximately 7 Mpc for θ_v < 10°, and to >13 Mpc for θ_v < 5°, a value much larger than the biggest giant radio galaxy known, which is 4.5 Mpc.

Conclusions. The above arguments suggest that PBC J2333.9-2343 has undergone a new episode of nuclear activity and that the direction of the new jet has changed in the plane of the sky and is now pointing towards us. This changes this source from a radio galaxy to a blazar, a very exceptional case of restarting activity.