IGR J17488–2338: a newly discovered giant radio galaxy

¹ IASF/INAF, via Gobetti 101, 40129 Bologna, Italy
e-mail: molina@iasfbo.inaf.it
² School of Physics and Astronomy, University of Southampton, SO17 1 BJ Southampton, UK
³ IAPS/INAF via Fosso del Cavaliere 100, 00133 Roma, Italy
⁴ IRA/INAF, via Gobetti 101, 40129 Bologna

Received: 10 February 2014
Accepted: 5 March 2014

Abstract

We present the discovery of a large-scale radio structure associated with IGR J17488–2338, a source recently discovered by INTEGRAL and optically identified as a broad-line AGN at redshift 0.24. At low frequencies, the source properties are those of an intermediate-power FR II radio galaxy with a linear size of 1.4 Mpc. This new active galaxy is therefore a member of a class of objects called giant radio galaxies (GRGs), a rare type of radio galaxy with physical sizes larger than 0.7 Mpc; they represent the largest and most energetic single entities in the Universe and are useful laboratories for many astrophysical studies. Their large-scale structures could be due either to special external conditions or to uncommon internal properties of the source central engine. The AGN at the centre of IGR J17488–2338 has a black hole of 1.3 × 10⁹ solar masses, a bolometric luminosity of 7 × 10⁴⁶ erg s^-1 and an Eddington ratio of 0.3, suggesting that it is powerful enough to produce the large structure observed in radio. The source is remarkable also for other properties, among which its X-ray absorption, at odds with its type 1 classification, and the presence of a strong iron line, which is a feature not often observed in radio galaxies.