The Relativistic Jet Orientation and Host Galaxy of the Peculiar Blazar PKS 1413+135

Abstract

PKS 1413+135 is one of the most peculiar blazars known. Its strange properties led to the hypothesis almost four decades ago that it is gravitationally lensed by a mass concentration associated with an intervening galaxy. It exhibits symmetric achromatic variability, a rare form of variability that has been attributed to gravitational milli-lensing. It has been classified as a BL Lac object, and is one of the rare objects in this class with a visible counterjet. BL Lac objects have jet axes aligned close to the line of sight. It has also been classified as a compact symmetric object-objects that have jet axes not aligned close to the line of sight. Intensive efforts to understand this blazar have hitherto failed to resolve even the questions of the orientation of the relativistic jet and the host galaxy. Answering these two questions is important because they challenge our understanding of jets in active galactic nuclei and the classification schemes we use to describe them. We show that the jet axis is aligned close to the line of sight and PKS 1413+135 is almost certainly not located in the apparent host galaxy, but is a background object in the redshift range 0.247<z<0.5. The intervening spiral galaxy at z=0.247 provides a natural host for the putative lens responsible for symmetric achromatic variability and is shown to be a Seyfert 2 galaxy. We also show that, as for the radio emission, a "multizone" model is needed to account for the highenergy emission.

Gamma-ray emission from young radio galaxies and quasars: the flaring episode of the peculiar galaxy PKS B1413+135

“…The detection of this flaring activity supports the idea that the -ray emission is beamed and produced by a relativistic jet at a relatively small viewing angle, similar to the case of the AGN PKS 0521−36 [28]. For the quasar PKS B1413+135 a recent study by Readhead et al [29] argues that the association with the spiral host galaxy is just due to a chance alignment, and instead supports the hypothesis that PKS B1413+135 is a background blazar-like object lying in the redshift range 0.247 < z < 0.5.…”

“…Gamma-rays from young radio galaxies and quasars Giacomo Principe only the normalization free to vary. Figure 2 shows the Fermi-LAT light curve for one-month time bins, compared to the 15 GHz radio lightcurve taken by the OVRO 40 m Telescope [29]. Its light curve reveals a strong -ray flare in the last year (2019) considered in this analysis.…”

What defines a compact symmetric object? A carefully vetted sample of compact symmetric objects

“…This brings us to the case of PKS 1413+135, which is what started us on this study. PKS 1413+135 is one of the most peculiar jetted-AGN known (Readhead et al, 2021), but its strange properties are outside the scope of this paper. It has frequently been discussed in the literature as a CSO and sometimes found to be unlike the other members of this class -see, for example Willett, Stocke, Darling, & Perlman (2010).…”

“…The equipartition angular size (Readhead et al, 2021;Scott & Readhead, 1977), eq in arc seconds, in a source showing a synchrotron self-absorption peak in the spectrum at Jy and MHz is…”

New Tests of Millilensing in the Blazar PKS 1413+135

“…In a companion paper (Vedantham et al 2017b), hereafter Paper 2, the possibility that SAV might be due to Extreme Scattering Events (ESEs) (Fiedler et al 1987(Fiedler et al , 1994 was definitively ruled out. It has been shown that the blazar PKS 1413+135 is almost certainly located behind an edge-on spiral Seyfert 2 galaxy at z=0.247 and that the blazar lies in the redshift range 0.247 < z < 0.5 (Readhead et al 2021), hereafter Paper 3. If PKS 1413+135 does indeed lie behind the Seyfert 2 galaxy, then the galaxy provides a natural host for the putative mass condensate responsible for the milli-lensing.…”