Compact Bright Radio-loud AGNs. III. A Large VLBA Survey at 43 GHz

Abstract

We present the observational results from the 43-GHz Very Long Baseline Array (VLBA) observations of 124 compact radio-loud active galactic nuclei (AGNs) that were conducted between 2014 November and 2016 May. The typical dimensions of the restoring beam in each image are about 0.5 mas × 0.2 mas. The highest resolution of 0.2 mas corresponds to a physical size of 0.02 pc for the lowest redshift source in the sample. The 43-GHz very long baseline interferometry (VLBI) images of 97 AGNs are presented for the first time. We study the source compactness on mas and sub-mas scales, and suggest that 95 sources in our sample are suitable for future space VLBI observations. By analyzing our data supplemented with other VLBA AGN surveys from literature, we find that the core brightness temperature increases with increasing frequency below a break frequency ∼7 GHz, and decreases between ∼7-240 GHz but increases -2again above 240 GHz in the rest frame of the sources. This indicates that the synchrotron opacity changes from optically thick to thin. We also find a strong statistical correlation between radio and γ-ray flux densities. Our correlation is tighter than those in literature derived from lower-frequency VLBI data, suggesting that the γ-ray emission is produced more co-spatially with the 43-GHz VLBA core emission. This correlation can also be extrapolated to the un-beamed AGN population, implying that a universal γ-ray production mechanism might be at work for all types of AGNs.

The Quasar CTD 135 is Not a Compact Symmetric Object

“…Remarkably, [22] estimate a Doppler factor δ = 10.8 for the core region. This is consistent with the value deduced from the 43-GHz VLBI observations [27]. For their SED fit, [22] assumed a compact core component and a homogeneous extended (5 mas) spherical emission region.…”

“…Indeed, as it is suggested by independent observational evidence collected in Section 2, CTD 135 shares its properties with blazars, AGN with relativistic jets pointed towards the observer. In particular, the existence of the compact flat/invertedspectrum SW component (Figure 2), clearly resolved with VLBI at 43 GHz and characterised by high brightness temperature [27], the highly variable γ-ray and mid-infrared emission, and the broad-band SED indicating Doppler-boosted emission [22] are all against the CSO classification tentatively proposed by [15].…”

“…The spectral index image was constructed using the VIMAP [29] tool that allows us to properly align the images made at two different frequencies. [27]. The peak brightness is 877 mJy beam −1 , the lowest contours are drawn at ±3 mJy beam −1 and the positive contour levels increase by a factor of 2.…”

Structural and spectral properties of Galactic plane variable radio sources

“…The sources G26.0526−0.2426, G22.9743−0.3920, G26.2818+0.2312 and G39.1105−0.0160 might also be faint blazars with flat-spectrum and variable radio cores (e.g. Ciaramella et al 2004;Cheng et al 2020). We cannot fully exclude the possibility of being bright non-thermal slow transients in their host galaxies, such as the decades-long transient FIRST J141918.9+394036 (Law et al 2018).…”

High-Frequency Polarization Variability from Active Galactic Nuclei

“…Regardless of the dominant mechanism that boosts the plasma into the jet stream, magnetic fields are a key ingredient to produce the jets that are observed in radio-loud AGN. In the presence of such strong magnetic fields, the energetic plasma particles radiate non-thermal (synchrotron) emission, which can reach very high brightness temperatures (as high as 10 10−13 K; e.g., [3,4]), especially in the compact core regions close to the jet base. Synchrotron emission can be strongly polarized, with an electric-vector position angle (EVPA) either perpendicular (in optically-thin media) or parallel (in media with high opacities) to the local magnetic field.…”