Faint gamma-ray sources at low redshift: the radio galaxy IC 1531

Abstract

We present a multiwavelength study of IC 1531 (z = 0.02564), an extragalactic radio source associated with the γ-ray object 3FGL J0009.9 − 3206 and classified as a blazar of uncertain type in the Third Fermi-Large Area Telescope AGN catalog (3LAC). A core-jet structure, visible in radio and X-rays, is enclosed within a ∼220 kpc wide radio structure. The morphology and spectral characteristics of the kiloparsec jet in radio and X-rays are typical of Fanaroff–Riley type I galaxies. The analysis of the radio data and optical spectrum and different diagnostic methods based on the optical, infrared, and γ-ray luminosities also support a classification as a low-power RG seen at moderate angles (θ = 10°–20°). In the framework of leptonic models, the high-energy peak of the non-thermal nuclear spectral energy distribution can be explained in terms of synchrotron-self-Compton emission from a jet seen at θ ∼ 15°. Similarly to other misaligned AGNs detected by Fermi, the required bulk motion is lower (Γbulk = 4) than the values inferred in BL Lac objects, confirming that, because of the de-boosting of emission from the highly relativistic blazar region, these nearby systems are valuable targets to probe the existence of multiple sites of production of the most energetic emission in the jets.

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