Mon. Not. R. Astron. Soc., 450, 3975-3990 (2015/July-2)
Unveiling the nature of the γ-ray emitting active galactic nucleus PKS 0521-36.
D'AMMANDO F., ORIENTI M., TAVECCHIO F., GHISELLINI G., TORRESI E., GIROLETTI M., RAITERI C.M., GRANDI P., ALLER M., ALLER H., GURWELL M.A., MALAGUTI G., PIAN E. and TOSTI G.
Abstract (from CDS):
PKS 0521-36 is an active galactic nucleus (AGN) with uncertain classification. We investigate the properties of this source from radio to γ-rays. The broad emission lines in the optical and ultraviolet bands and steep radio spectrum indicate a possible classification as an intermediate object between broad-line radio galaxies (BLRG) and steep spectrum radio quasars (SSRQ). On pc-scales PKS 0521-36 shows a knotty structure similar to misaligned AGN. The core dominance and the γ-ray properties are similar to those estimated for other SSRQ and BLRG detected in γ-rays, suggesting an intermediate viewing angle with respect to the observer. In this context the flaring activity detected from this source by Fermi-Large Area Telescope between 2010 June and 2012 February is very intriguing. We discuss the γ-ray emission of this source in the framework of the structured jet scenario, comparing the spectral energy distribution (SED) of the flaring state in 2010 June with that of a low state. We present three alternative models corresponding to three different choices of the viewing angles θv = 6°, 15°, and 20°. We obtain a good fit for the first two cases, but the SED obtained with θv = 15° if observed at a small angle does not resemble that of a typical blazar since the synchrotron emission should dominate by a large factor ( ∼ 100) the inverse Compton component. This suggests that a viewing angle between 6° and 15° is preferred, with the rapid variability observed during γ-ray flares favouring a smaller angle. However, we cannot rule out that PKS 0521-36 is the misaligned counterpart of a synchrotron-dominated blazar.
© 2015 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society (2015)
galaxies: active - galaxies: individual: PKS 0521-36 - galaxies: nuclei - quasars: general - gamma-rays: galaxies - gamma-rays: general
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