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We present a comprehensive variability study on three blazars, S4 0954+65, PKS 0903−57, and 4C +01.02, covering a mass range of log(M /M⊙) = 8–9, by using ∼15-yr-long γ-ray LCs from Fermi -LAT. The variability level is characterized by the fractional variability amplitude that is higher for γ-rays compared with optical/UV and X-rays emissions. A power spectral density (PSD) study and damped random walk (DRW) modelling are done to probe the characteristic time-scale. The PSD is fitted with a single power law (PL) and bending PL models and the corresponding success fraction was estimated. In the case of PKS 0903−57, We observed a break in the γ-ray PSD at 256 d, which is comparable to the viscous time-scale in the accretion disc, suggesting a possible disc–jet coupling. The non-thermal damping time-scale from the DRW modelling is compared with the thermal damping time-scale for AGNs including our three sources. Our sources lie on the best fit of the |$\mathrm{\tau ^{\rm rest}_{\rm damping}}\!-\!M_{\rm BH}$| plot derived for AGN, suggesting a possible accretion disc–jet connection. If the jet's variability is linked to the disc's variability, we expect a log-normal flux distribution, often connected to the accretion disc's multiplicative processes. Our study observed a double log-normal flux distribution, possibly linked to long- and short-term variability from the accretion disc and the jet. In summary, PSD and DRW modelling results for these three sources combined with blazars and AGNs studied in literature favour a disc–jet coupling scenario. However, more such studies are needed to refine this understanding. [ABSTRACT FROM AUTHOR]

In this study, we carry out a comprehensive variability analysis of the BL Lac object 4FGL J2202.7+4216 detected by the Fermi- LAT, over a period of more than 3 yr, from 2019 April 27 to 2022 August 09. We detect the presence of quasi-periodic fluctuations with a period of ∼100 d with a confidence level exceeding 4σ. We also tentatively detect two other quasi-periodic fluctuations with a period of ∼75 and ∼50 d, which persist over the entire duration of observation. This is the first time such a variability feature pertaining to this source is being reported. We propose that the observed quasi-periodic oscillations may be related to the precession of the blazar jet with a high Lorentz factor or to the motion of a plasma blob through the helical structure of the jet. The harmonicity among the detected periodicities suggests the global p-mode oscillations of the thick disc to be a plausible mechanism as well. For a decisive conclusion on the physical origin of such fluctuation, further multiwavelength complementary observations, especially very long baseline interferometric observations, would be required. [ABSTRACT FROM AUTHOR]

It is still controversial whether the x‐ray emissions of strong radio black hole sources (e.g., blazars and FR Is) are from a jet‐dominated flow or from an accretion disc. Previous studies have suggested that the radio–x‐ray correlation is clearly different when the x‐ray luminosity is higher or lower than a critical value, LX,crit∼10−3LEdd$$ {L}_{\mathrm{X},\mathrm{crit}}\sim {10}^{-3}{L}_{\mathrm{Edd}} $$, where LEdd∼1.28×1038ergs−1$$ {L}_{\mathrm{Edd}}\sim 1.28\times {10}^{38}\mathrm{erg}\kern0.3em {\mathrm{s}}^{-1} $$ is the Eddington luminosity. When the black hole transient sources stay in quiescent state (LX,crit≤10−6LEdd$$ {L}_{\mathrm{X},\mathrm{crit}}\le {10}^{-6}{L}_{\mathrm{Edd}} $$), the radio–x‐ray correlation presented a steeper slope (LR∝LXb,b∼1.23$$ {L}_{\mathrm{R}}\propto {L}_{\mathrm{X}}^b,b\sim 1.23 $$). In this work, we constructed a strong radio sample, including blazars and FR Is with a wide x‐ray luminosity distribution (LX∼10−7−10−1LEdd$$ {L}_{\mathrm{X}}\sim {10}^{-7}-{10}^{-1}{L}_{\mathrm{Edd}} $$) to re‐explore this issue. An obvious change in radio–x‐ray correlations is not found when the x‐ray luminosity LX,crit∼10−3LEdd$$ {L}_{\mathrm{X},\mathrm{crit}}\sim {10}^{-3}{L}_{\mathrm{Edd}} $$ and LX,crit∼10−6LEdd$$ {L}_{\mathrm{X},\mathrm{crit}}\sim {10}^{-6}{L}_{\mathrm{Edd}} $$. And the radio–x‐ray correlation and the fundamental plane of black hole activity for strong radio sources follow a slope with ξX=1.24±0.03$$ {\xi}_{\mathrm{X}}=1.24\pm 0.03 $$. These results imply x‐ray emissions of strong radio black hole sources have similar physics and can be well explained by a jet‐dominated flow. [ABSTRACT FROM AUTHOR]

We report the detection (>4σ) of a quasi-periodic oscillation (QPO) in the gamma-ray light curve of 3C 454.3 along with a simultaneous marginal QPO detection (>2.4σ) in the optical light curves. Periodic flux modulations were detected in both of these wavebands with a dominant period of ∼47 d. The gamma-ray QPO lasted for over 450 d (from MJD 56800 to 57250), resulting in over nine observed cycles which is among the highest number of periods ever detected in a blazar light curve. The optical light curve was not well sampled for almost half of the gamma-ray QPO span due to the daytime transit of the source, which could explain the lower significance of the optical QPO. Autoregressive Integrated Moving Average (ARIMA) modelling of the light curve revealed a significant, exponentially decaying, trend in the light curve during the QPO, along with the 47 d periodicity. We explore several physical models to explain the origin of this transient quasi-periodic modulation and the overall trend in the observed flux with a month-like period. These scenarios include a binary black hole system, a hotspot orbiting close to the innermost stable circular orbit of the supermassive black hole, and precessing jets. We conclude that the most likely scenario involves a region of enhanced emission moving helically inside a curved jet. The helical motion gives rise to the QPO and the curvature (∼0.05○ pc−1) of the jet is responsible for the observed trend in the light curve. [ABSTRACT FROM AUTHOR]

A small subset of optically selected radio-quiet quasars showing weak or no emission lines may turn out to be the elusive radio-quiet BL Lac objects, or simply be radio-quiet QSOs with a still-forming/shielded broad line region (BLR). High polarization (p > 3–4 per cent), a hallmark of BL Lacs, can be used to test whether some optically selected ‘radio-quiet weak emission line quasars’ (RQWLQs) show a fractional polarization high enough to qualify as radio-quiet analogues of BL Lac objects. Out of the observed six RQWLQs candidates showing an insignificant proper motion, only two are found to have p > 1 per cent. For these two RQWLQs, namely J142505.59 + 035336.2 and J154515.77+003235.2, we found polarization of 1.03 ± 0.36 per cent and 1.59 ± 0.53 per cent, respectively, which again is too modest to justify a (radio-quiet) BL Lac classification. We also present here a statistical comparison of the optical spectral index, for a set of 40 RQWLQs with redshift-luminosity matched control sample of 800 QSOs and an equivalent sample of 120 blazars. The spectral index distribution of RQWLQs is found to differ, at a high significance level, from that of blazars and is consistent with that of the ordinary QSOs. Likewise, a structure–function analysis of photometric light curves presented here suggests that the mechanism driving optical variability in RQWLQs is similar to that operating in QSOs and different from that of blazars. These findings are consistent with the common view that the central engine in RQWLQs, as a population, is akin to that operating in normal QSOs and the primary differences between them might be related to differences in the BLR. [ABSTRACT FROM AUTHOR]

We present the first data release of high-resolution (≤0.2 arcsec) 1.5-GHz radio images of 103 nearby galaxies from the Palomar sample, observed with the eMERLIN array, as part of the LeMMINGs survey. This sample includes galaxies which are active (low-ionization nuclear emission-line regions [LINER] and Seyfert) and quiescent (H  ii galaxies and absorption line galaxies, ALGs), which are reclassified based upon revised emission-line diagrams. We detect radio emission ≳0.2 mJy for 47/103 galaxies (22/34 for LINERS, 4/4 for Seyferts, 16/51 for H  ii galaxies, and 5/14 for ALGs) with radio sizes typically of ≲100 pc. We identify the radio core position within the radio structures for 41 sources. Half of the sample shows jetted morphologies. The remaining half shows single radio cores or complex morphologies. LINERs show radio structures more core-brightened than Seyferts. Radio luminosities of the sample range from 1032 to 1040 erg s−1: LINERs and H  ii galaxies show the highest and lowest radio powers, respectively, while ALGs and Seyferts have intermediate luminosities. We find that radio core luminosities correlate with black hole (BH) mass down to ∼107 M⊙, but a break emerges at lower masses. Using [O  iii ] line luminosity as a proxy for the accretion luminosity, active nuclei and jetted H  ii galaxies follow an optical Fundamental Plane of BH activity, suggesting a common disc–jet relationship. In conclusion, LINER nuclei are the scaled-down version of FR I radio galaxies; Seyferts show less collimated jets; H  ii galaxies may host weak active BHs and/or nuclear star-forming cores; and recurrent BH activity may account for ALG properties. [ABSTRACT FROM AUTHOR]

We present a model-dependent method to estimate the red shifts of three TeV BL Lac objects (BL Lacs) through fitting their (quasi-)simultaneous multi-waveband spectral energy distributions (SEDs) with a one-zone leptonic synchrotron self-Compton model. Considering the impact of electron energy distributions (EEDs) on the results, we use three types of EEDs to fit the SEDs: a power-law EED with exponential cut-off (PLC), a log-parabola (PLLP) EED and the broken power-law (BPL) EED. We also use a parameter a to describe the uncertainties of the extragalactic background light models, as in Abdo et al. We then use a Markov chainMonte Carlo method to explore the multi-dimensional parameter space and obtain the uncertainties of the model parameters based on the observational data. We apply our method to obtain the red shifts of three TeV BL Lac objects in the marginalized 68 per cent confidence, and find that the PLC EED does not fit the SEDs. For 3C66A, the red shift is 0.14-0.31 and 0.16-0.32 in the BPL and PLLP EEDs. For PKS1424+240, the red shift is 0.55-0.68 and 0.55-0.67 in the BPL and PLLP EEDs. For PG1553+113, the red shift is 0.22-0.48 and 0.22-0.39 in the BPL and PLLP EEDs. We also estimate the red shift of PKS1424+240 in the high stage to be 0.46-0.67 in the PLLP EED, roughly consistent with that in the low stage. [ABSTRACT FROM AUTHOR]

We present the results from a broad-band (1 to 3 GHz), spectro-polarimetry study of the integrated emission from 100 extragalactic radio sources with the Australia Telescope Compact Array, selected to be highly linearly polarized at 1.4 GHz. We use a general-purpose, polarization model-fitting procedure that describes the Faraday rotation measure (RM) and intrinsic polarization structure of up to three distinct polarized emission regions or 'RM components' of a source. Overall, 37 per cent/52 per cent/11 per cent of sources are best fitted by one/two/three RMcomponents. However, these fractions are dependent on the signal-to-noise ratio (S/N) in polarization (more RM components more likely at higher S/N). In general, our analysis shows that sources with high integrated degrees of polarization at 1.4 GHz have low Faraday depolarization, are typically dominated by a single RM component, have a steep spectral index and have a high intrinsic degree of polarization. After classifying our sample into radiative-mode and jet-mode AGN, we find no significant difference between the Faraday rotation or Faraday depolarization properties of jet-mode and radiative-mode AGN. However, there is a statistically significant difference in the intrinsic degree of polarization between the two types, with the jet-mode sources having more intrinsically ordered magnetic field structures than the radiative-mode sources. We also find a preferred perpendicular orientation of the intrinsic magnetic field structure of jet-mode AGN with respect to the jet direction, while no clear preference is found for the radiative-mode sources. [ABSTRACT FROM AUTHOR]

Multifrequency Very Long Baseline Array (VLBA) polarimetry observation of the GHz-peaked spectrum (GPS) quasar OQ172 (J1445+0958) has been performed at 1.6, 2.2, 4.8, 8.3 and 15.3 GHz in 2005. Core-jet structures are detected in all bands with the jet strongly bent at about 3 mas from the core. The radio emission of the source is polarized at all five bands. We study the Faraday rotation in the core and jet components at all five bands, and find good linear fits of Faraday rotation in the core and jet components at 4.8 and 8.3 GHz. At these two frequencies, the rotation measure (RM) is ~2000 rad m-2 in the core and ~700 rad m-2 in the inner jet components and continues to decrease at the outer jet parts. We find that the depolarization at 4.8 and 8.3 GHz might be caused by the internal medium in the source. We investigate consistency of the turnover spectra of VLBI components with the synchrotron self-absorption and free-free absorption models. Although these two models cannot be easily distinguished due to the lack of low-frequency data, the physical parameters can be constrained for each model. We find that the large width of the [O III]5007 line is likely caused by a jet interaction with a narrow line region (NLR) medium. The jet bending, significant RM variations, Faraday depolarization, spectral turnover and broad line width of [O III]5007 could be closely related, likely caused by the same nucleus medium, presumably NLR. [ABSTRACT FROM AUTHOR]

We report an extension of our programme to search for radio-quiet BL Lac candidates using intranight optical variability (INOV) as a probe. The present INOV observations cover a welldefined representative set of 10 'radio-quiet weak-emission-line quasars' (RQWLQs), selected from a newly published sample of 46 such sources, derived from the Sloan Digital Sky Survey (Data release 7). Intranight CCD monitoring of the 10 RQWLQs was carried out in 18 sessions lasting at least 3.5 h. For each session, differential light curves of the target RQWLQ were derived relative to two steady comparison stars monitored simultaneously. Combining these new data with those already published by us for 15 RQWLQs monitored in 30 sessions, we estimate an INOV duty cycle of~3 per cent for the RQWLQs, which appears inconsistent with BL Lacs. However, the observed INOV events (which occurred in just two of the sessions) are strong (with a fractional variability amplitudeψ >10 per cent), hence blazar-like. We briefly point out the prospects of an appreciable rise in the estimated INOV duty cycle for RQWLQs with a relatively modest increase in sensitivity for monitoring these rather faint objects. [ABSTRACT FROM AUTHOR]

We investigate the connections between radio, optical and soft X-ray luminosities with a sample of 538 FSRQs. We find that the radio luminosity is strongly correlated with the optical luminosity, as well as with the soft X-ray luminosity. We also find that the optical luminosity is strongly correlated with the soft X-ray luminosity. [ABSTRACT FROM AUTHOR]

In this work, we employ a sample of 185 steep-spectrum radio quasars (SSRQs) to estimate their black hole masses from broad emission lines. Our black hole masses are compared with the virial black hole masses estimated by Shen (2010). We find that there is a large deviation between the two kinds of values if the black hole masses are estimated from broad emission line of CIV. However, both values are in agreement if the black hole masses are estimated from broad emission line of MgII or H β. [ABSTRACT FROM AUTHOR]

We present a numerical code, written in C, which can be used to simulate or to analyze the emission of Blazars over the entire electromagnetic spectrum. Our code can reproduce: Synchrotron emission, Inverse Compton emission (IC) (Thomson & Klein-Nishina regime), External Compton emission (EC), accretion disk variability using a Cellular Automata (CA) algorithm, temporal evolution of the emitting plasma energy distribution, flaring phenomena, light curves in the rest and in the observer frame (taking account for time crossing effects). [Copyright &y& Elsevier]

We explore the connection between the black hole mass and its relativistic jet for a sample of radio-loud AGN (z < 1), in which the relativistic jet parameters are well estimated by means of long term monitoring with the 14m Metsähovi millimeter wave telescope and the Very Long Base-line Array (VLBA). NIR host galaxy images taken with the NOTCam on the Nordic Optical Telescope (NOT) and retrieved from the 2MASS all-sky survey allowed us to perform a detailed surface brightness decomposition of the host galaxies in our sample and to estimate reliable black hole masses via their bulge luminosities. We present early results on the correlations between black hole mass and the relativistic jet parameters. Our preliminary results suggest that the more massive the black hole is, the faster and the more luminous jet it produces. [ABSTRACT FROM PUBLISHER]

Accreting supermassive black holes and starburst regions influence their host galaxies through kinetic/radiative feedback processes. To better understand the gas evolution of a Seyfert galaxy, in this study we perform fully 3D hydrodynamical simulations with radiative cooling considering the presence of star formation regions, supernova feedback and small-scale (1 kpc) jet propagation in the central region of an active spiral galaxy. We compute the gas mass lost by the system and we conclude that a kpc-scale outflow is generally established only when a nuclear starburst region is coupled to a supermassive black hole jet. [ABSTRACT FROM PUBLISHER]