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Accretion of black holes at near-Eddington or super-Eddington rates represents the most powerful episode driving black hole growth, potentially occurring across various types of objects. However, the physics governing accretion and jet–disk coupling in such states remains unclear, primarily due to the difficulty in detecting associated jets, which may emit extremely weakly or exhibit episodic behavior. Only a few near/super-Eddington systems have demonstrated radio activity, and it remains uncertain whether jets exist and what their properties are in super-Eddington active galactic nuclei (AGNs) and ultraluminous X-ray sources. This uncertainty stems mainly from the complex radio emission mix, which includes contributions from jets, star formation activity, photoionized gas, accretion disk wind, and coronal activity. In this work, we conducted high-resolution, very long baseline interferometry observations to investigate jets in the highly accreting narrow-line Seyfert I system I Zw 1. Our observations successfully revealed small-scale jets (with a linear size of ∼45 pc) at both 1.5 and 5 GHz, based on the high radio brightness temperature, radio morphology, and spectral index distribution. Additionally, the parsec-scale jet observed in I Zw 1 displays a knotted morphology reminiscent of other sources accreting at similar rates. In summary, the high accretion rates and jet properties observed in the AGN I Zw 1 may support the AGN/X-ray binary analogy in this extreme state. [ABSTRACT FROM AUTHOR]

We present multiband follow-up observations of the supermassive binary black hole (BBH) candidate and misaligned double–double radio galaxy, J1328+2752. To investigate its parsec-scale structure, we have carried out observations with the Very Long Baseline Array (VLBA) and the European Very Long Baseline Interferometry (VLBI) Network. Additionally, we have obtained optical spectroscopic observations with the 3.6 m Devasthal Optical Telescope. Within 3.5 yr of our previous VLBI observations, the central parsec-scale radio structure of J1328+2752 has changed from a double component to a single central component and its flux density has increased by a factor of 3 in the 5 GHz VLBA observations. The new radio component is largely unresolved at 3, 5, and 8 GHz. The multifrequency radio data shows a convex-shaped spectrum for this unresolved component. The turnover frequency is at ∼3 GHz. While the total intensity image does not reveal any details, a super-resolved VLBA 5 and 8 GHz spectral index image does indicate the presence of two components at a separation of ∼4.2 pc with spectral indices −0.5 ± 0.3 and −0.9 ± 0.3. We have not observed a simultaneous change in the optical line profiles or intensities over the past few years. The radio structure, the variation of the flux density, and spectral shape can potentially be consistent both with the signature of a young radio source or a BBH at the center of J1328+2752. [ABSTRACT FROM AUTHOR]

We explored the parsec-scale nuclear regions of a sample of radio-loud narrow-line Seyfert 1 galaxies (NLSy1s) using the VLBI Exploration of Radio Astrometry wideband (at a recording rate of 16 Gbps) polarimetry at 22 and 43 GHz. Our targets include 1H 0323+342, SBS 0846+513, PMN J0948+0022, 1219+044, PKS 1502+036, and TXS 2116-077, which are all known to exhibit γ -ray emission indicative of possessing highly beamed jets similar to blazars. For the first time, we unambiguously detected Faraday rotation toward the parsec-scale radio core of NLSy1s, with a median observed core rotation measure (RM) of 2.7 × 103 rad m−2 (or 6.3 × 103 rad m−2 for redshift-corrected). This level of RM magnitude is significantly larger than those seen in the core of BL Lacertae objects (BLOs; a dominant subclass of blazars), suggesting that the nuclear environment of NLSy1s is more gas-rich than that in BLOs. Interestingly, the observed parsec-scale polarimetric properties of NLSy1s (low core fractional polarization, large core RM and jet–EVPA misalignment) are rather similar to those of flat-spectrum radio quasars (FSRQs). Our results are in accordance with the scenario that NLSy1s are in an early stage of active galactic nucleus evolution with their central black hole masses being smaller than those of more evolved FSRQs. [ABSTRACT FROM AUTHOR]

We present results from the first 22 GHz space very long baseline interferometric (VLBI) imaging observations of M87 by RadioAstron. As a part of the Nearby AGN Key Science Program, the source was observed in 2014 February at 22 GHz with 21 ground stations, reaching projected (u, v) spacings up to ∼11 G λ. The imaging experiment was complemented by snapshot RadioAstron data of M87 obtained during 2013–2016 from the AGN Survey Key Science Program. Their longest baselines extend up to ∼25 G λ. For all of these measurements, fringes are detected only up to ∼2.8 Earth diameter or ∼3 G λ baseline lengths, resulting in a new image with angular resolution of ∼150 μ as or ∼20 Schwarzschild radii spatial resolution. The new image not only shows edge-brightened jet and counterjet structures down to submilliarcsecond scales but also clearly resolves the VLBI core region. While the overall size of the core is comparable to those reported in the literature, the ground-space fringe detection and slightly superresolved RadioAstron image suggest the presence of substructures in the nucleus, whose minimum brightness temperature exceeds T B , min ∼ 10 12 K. It is challenging to explain the origin of this record-high T B , min value for M87 by pure Doppler boosting effect with a simple conical jet geometry and known jet speed. Therefore, this can be evidence for more extreme Doppler boosting due to a blazar-like small jet viewing angle or highly efficient particle acceleration processes occurring already at the base of the outflow. [ABSTRACT FROM AUTHOR]

The combined study of the flaring of active galactic nuclei (AGNs) at radio wavelengths and parsec-scale jet kinematics with Very Long Baseline Interferometry has led to the view that (i) the observed flares are associated with ejections of synchrotron blobs from the core, and (ii) most of the flaring follows a one-to-one correlation with the ejection of the component. Recent results have added to the mounting evidence showing that the quasi-regular component injections into the relativistic jet may not be the only cause of the flux variability. We propose that AGN flux variability and changes in jet morphology can both be of deterministic nature, i.e., having a geometric/kinetic origin linked to the time-variable Doppler beaming of the jet emission as its direction changes due to precession (and nutation). The physics of the underlying jet leads to shocks, instabilities, or ejections of plasmoids. The appearance (morphology, flux, etc.) of the jet can, however, be strongly affected and modulated by precession. We demonstrate this modulating power of precession for OJ 287. For the first time, we show that the spectral state of the spectral energy distribution (SED) can be directly related to the jet's precession phase. We model the SED evolution and reproduce the precession parameters. Further, we apply our precession model to 11 prominent AGNs. We show that for OJ 287 precession seems to dominate the long-term variability (≳1 yr) of the AGN flux, SED spectral state, and jet morphology, while stochastic processes affect the variability on short timescales (≲0.2 yr). [ABSTRACT FROM AUTHOR]

We report the results of Atacama Large Millimeter/submillimeter Array (ALMA) 1–2 kpc resolution, three rotational transition-line (J = 2–1, J = 3–2, and J = 4–3) observations of multiple dense molecular gas tracers (HCN, HCO+, and HNC) for 10 nearby (ultra)luminous infrared galaxies ((U)LIRGs). Following the matching of beam sizes to 1–2 kpc for each (U)LIRG, the high- J -to-low- J transition-line flux ratios of each molecule and the emission-line flux ratios of different molecules at each J transition are derived. We conduct RADEX non-LTE model calculations and find that, under a wide range of gas density and kinetic temperature, the observed HCN-to-HCO+ flux ratios in the overall (U)LIRGs are naturally reproduced with enhanced HCN abundance compared to HCO+. Thereafter, molecular gas properties are constrained primarily through the use of HCN and HCO+ data and the adoption of fiducial values for the HCO+ column density and HCN-to-HCO+ abundance ratio. We quantitatively confirm the following: (i) molecular gas at the (U)LIRGs' nuclei is dense (≳103–4 cm−3) and warm (≳100 K), (ii) the molecular gas density and temperature in nine ULIRGs' nuclei are significantly higher than those of one LIRG's nucleus, (iii) molecular gas in starburst-dominated sources tends to be less dense and cooler than ULIRGs with luminous AGN signatures. For six selected sources, we also apply a Bayesian approach by freeing all parameters and support the above main results. Our ALMA 1–2 kpc resolution, multiple transition-line data of multiple molecules are a very powerful tool for scrutinizing the properties of molecular gas concentrated around luminous energy sources in nearby (U)LIRGs' nuclei. [ABSTRACT FROM AUTHOR]