The flat spectrum radio quasar (FSRQ) PKS 2123−463 was associated in the first Fermi-Large Area Telescope (LAT) source catalogue with the γ-ray source 1FGL J2126.1−4603, but when considering the full first two years of Fermi observations, no γ-ray source at a position consistent with this FSRQ was detected, and thus PKS 2123−463 was not reported in the second Fermi-LAT source catalogue. On 2011 December 14 a γ-ray source positionally consistent with PKS 2123−463 was detected in flaring activity by Fermi-LAT. This activity triggered radio-to-X-ray observations by the Swift, Gamma-ray Optical/Near-Infrared Detector (GROND), Australia Telescope Compact Array (ATCA), Ceduna and Seven Dishes Karoo Array Telescope (KAT-7) observatories. Results of the localization of the γ-ray source over 41 months of Fermi-LAT operation are reported here in conjunction with the results of the analysis of radio, optical, ultraviolet (UV) and X-ray data collected soon after the γ-ray flare. The strict spatial association with the lower energy counterpart together with a simultaneous increase of the activity in optical, UV, X-ray and γ-ray bands led to a firm identification of the γ-ray source with PKS 2123−463. A new photometric redshift has been estimated as z = 1.46 ± 0.05 using GROND and Swift Ultraviolet/Optical Telescope (UVOT) observations, in rough agreement with the disputed spectroscopic redshift of z = 1.67. We fit the broad-band spectral energy distribution with a synchrotron/external Compton model. We find that a thermal disc component is necessary to explain the optical/UV emission detected by Swift/UVOT. This disc has a luminosity of ∼1.8 × 10⁴⁶ erg s⁻¹, and a fit to the disc emission assuming a Schwarzschild (i.e. non-rotating) black hole gives a mass of ∼2 × 10⁹ M⊙. This is the first black hole mass estimate for this source.

Item Type:	Refereed Article
Keywords:	galaxies: active; galaxies: nuclei; quasars: general; quasars: individual: PKS 2123-463; gamma rays: general
Research Division:	Physical Sciences
Research Group:	Astronomical and Space Sciences
Research Field:	Cosmology and Extragalactic Astronomy
Objective Division:	Expanding Knowledge
Objective Group:	Expanding Knowledge
Objective Field:	Expanding Knowledge in the Physical Sciences
UTAS Author:	Blanchard, JM (Mr Jay Blanchard)
UTAS Author:	Lovell, JEJ (Dr Jim Lovell)
ID Code:	83102
Year Published:	2012
Web of Science® Times Cited:	7
Deposited By:	Mathematics and Physics
Deposited On:	2013-03-01
Last Modified:	2017-11-01
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