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1

A Survey Length for AGN Variability Studies

Kozłowski S.

Acta Astronomica

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2021

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Vol. 71, No. 2

103--112

EN

The damped random walk (DRW) process is one of the most commonly used and simplest stochastic models to describe variability of active galactic nuclei (AGN). An AGN light curve can be converted to just two DRW model parameters - the signal decorrelation timescale τ and the asymptotic amplitude SF∞. In principle, these two model parameters may be correlated with the physical parameters of AGN. By simulation means, we have recently shown that in order to measure the decorrelation timescale accurately, the experiment or the light curve length must be at least 10 times the underlying decorrelation timescale. In this paper, we investigate the origin of this requirement and find that typical AGN light curves do not sufficiently represent the intrinsic stationary process. We simulated extremely long (10 000τ) AGN light curves using DRW, and then measured the variance and the mean of short light curves spanning 1-1000τ. We modeled these light curves with DRW to obtain both the signal decorrelation timescale τ and the asymptotic amplitude SF∞. The variance in light curves shorter than ≈30τ is smaller than that of the input process, as estimated by both a simple calculation from the light curve and by DRW modeling. This means that while the simulated stochastic process is intrinsically stationary, short light curves do not adequately represent the stationary process. Since the variance and timescale are correlated, underestimated variances in short light curves lead to underestimated timescales as compared to the input process. It seems, that a simulated AGN light curve does not fully represent the underlying DRW process until its length reaches even ≈30 decorrelation timescales. Modeling short AGN light curves with DRW leads to biases in measured parameters of the model - the amplitude being too small and the timescale being too short.

2

Merger Signatures in Radio Loud and Radio Quiet Quasars

Garofalo D., Webster B., Bishop K.

Acta Astronomica

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2020

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Vol. 70, No. 1

75--85

EN

While the origin of the radio loud/radio quiet dichotomy is still debated, the consensus is that radio loud and radio quiet quasars are both triggered by mergers, yet merger signatures are not evenly distributed among the two groups. Whereas they are detected in radio loud quasars at a rate of 80-100%, the rate is considerably smaller in radio quiet quasars at 20-30%. Because the radio loud/radio quiet dichotomy is a counterrotation/co-rotation accretion dichotomy around spinning black holes in our paradigm, and counterrotation spins black holes down rapidly, radio loud quasars live comparably shorter lifetimes. As a result, they are more likely to be observed when less time elapses from the merger that triggered them. In order to check our model, we work backwards from the observed merger rates to obtain accretion rates for both the jetted and non-jetted quasars in our model. The goal is to check the model prescription that both families of active galaxies accrete at a rate that is compatible with cold, radiatively efficient, thin disks. We find that if average accretion rates in radio loud quasars span the range 2-80% of the Eddington accretion rate, we obtain a match with the observed 80-100% rate of merger signatures. Because radio quiet quasars emerge in different ways in the model with phases whose lifetimes vary by much more, from a few million to a billion years, the rates of merger signatures are more difficult to obtain. Nonetheless, we show that for the radio quiet quasars with longest lifetimes that should dominate the merger signature rates, average accretion rates in the range 5-7.5% of the Eddington limit make theory compatible with observations. Interestingly, these numbers are compatible with the assumption in the model that the relevant radio quiet quasars in the analysis live longer and therefore experience a decline in accretion rate over time.

3

1.4-GHz Observations of Extended Giant Radio Galaxies

Weżgowiec M., Jamrozy M., Mack K.-H.

Acta Astronomica

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2016

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Vol. 66, No. 1

85--119

EN

This paper presents 1.4-GHz radio continuum observations of fifteen very extended radio galaxies. These sources are so large that most interferometers lose partly their structure and total flux density. Therefore, single-dish detections are required to fill in the central (u,v) gap of interferometric data and obtain reliable spectral index patterns across the structures, and thus also an integrated radio continuum spectrum. We have obtained such 1.4-GHz maps with the 100-m Effelsberg telescope and combined them with the corresponding maps available from the NVSS. The aggregated data allow us to produce high-quality images, which can be used to obtain physical parameters of the mapped sources. The combined images reveal in many cases extended low surface-brightness cocoons.

4

Empirical Conversions of Broad-Band Optical and Infrared Magnitudes to Monochromatic Continuum Luminosities for Active Galactic Nuclei

Kozłowski S.

Acta Astronomica

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2015

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Vol. 65, No. 3

251--265

EN

We use public data for 105 783 quasars from The Sloan Digital Sky Survey (SDSS) Data Release 7 (DR7) that include spectral monochromatic luminosities at 5100 Å, 3000 Å, and 1350 Å, and the corresponding observed broad-band ugriz, VRI (converted), JHK and WISE magnitudes, and derive broad-band-to-monochromatic luminosity ratios independent of a cosmological model. The ratios span the redshift range of z = 0.1 ÷ 4.9 and may serve as a proxy for measuring the bolometric luminosity, broad line region (BLR) radii and/or black hole masses, whenever flux-calibrated spectra are unavailable or the existing spectra have low signal-to-noise ratios. They are provided both in tabular and parametric form.

5

J1145-0033 - The Most Distant Giant Radio Source?

Kuźmicz A., Kuligowska E., Jamrozy M.

Acta Astronomica

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2011

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Vol. 61, No. 1

71--82

EN

We present J1145-0033, a candidate for the most distant (z=2.055) lobe-dominated giant radio quasar, with a projected linear size of 1.34 Mpc. This quasar has both FRII-type radio morphology and broad absorption lines in its optical spectrum. Some physical characteristics (e.g., black hole mass, accretion rate, equipartition magnetic field, energy density and particle density of ambient medium) based on the optical and radio data are provided. We have also found that the quasar has a relatively large central black hole mass and a very small accretion rate in comparison with similar objects.

6

Giant Radio Sources in View of the Dynamical Evolution of FRII-type Population. I. The Observational Data and Basic Physical Parameters of Sources Derived from the Analytical Model

Machalski J., Chyży K. T., Jamrozy M.

Acta Astronomica

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2004

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Vol. 54, No. 3

249--279

EN

The time evolution of giant lobe-dominated radio galaxies (with projected linear size D>1 Mpc if H0=50 km/s Mpc and q0=0.5) is analyzed on the basis of dynamical evolution of the entire FRII-type population. Two basic physical parameters, namely the jet power Q0 and central density of the galaxy nucleus ρ0 are derived for a sample of giants with synchrotron ages reliably determined, and compared with the relevant parameters in a comparison sample of normal-size sources consisting of 3C, B2, and other sources. Having the apparent radio luminosity P and linear size D of each sample source, Q0 and ρ0 are obtained by fitting the dynamical model of Kaiser et al. We find that: (i) There is no unique factor governing the source size. The sources are old, with temperate jet power (Q0) and are evolved in a relatively low-density environment (ρ0). The size is dependent, in order of decreasing partial correlation coefficients, on age, then on Q0, next on ρ0. (ii) A self-similar expansion of the sources' cocoon seems to be feasible if the power supplied by the jets is a few orders of magnitude above the minimum-energy value. In other cases the expansion can only initially be self-similar, a departure from self-similarity for large and old sources is justified by observational data of giant sources. (iii) An apparent increase of the lowest internal pressure value observed within the largest sources' cocoon with redshift is obscured by the intrinsic dependence of their size on age and the age on redshift, which hinders us from making definite conclusions about a cosmological evolution of intergalactic medium (IGM) pressure.

7

Giant Radio Sources in View of the Dynamical Evolution of FRII-Type Population. II. The Evolutionary Tracks on the P-D and uc - Etot Planes

Machalski J., Chyży K. T., Jamrozy M.

Acta Astronomica

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2004

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Vol. 54, No. 4

391--403

EN

The time evolution of "fiducial" radio sources derived from fitting the dynamical model of Kaiser et al. (1997) is compared with the observational data for the "clan" sources found in the sample of giant and normal-size FRII-type sources published in Paper I (Machalski et al. 2004). Each "clan" comprises 3, 4 or 5 sample sources having similar values of the two basic physical parameters: the jet power Q0 and central density of the galaxy nucleus ρ0 (determined in Paper I) but different ages, radio luminosities and axial ratios. These sources are considered as the "same" source observed at different epochs of its lifetime and used to fit the evolutionary luminosity-size (P-D) and energy density-total energy (uc-Etot) tracks derived from the model for a "fiducial" source with Q0 and ρ0 equal to the averages of relevant values obtained for the "clan" members, as well as to constrain the evolutionary model of the source dynamics used. In the result we find that (i) the best fit is achieved when the Kaiser et al.'s model is modified by allowing an evolution of the sources' cocoon axial ratio with time as suggested by Blundell et al. (1999), (ii) a slow acceleration of the average expansion speed of the cocoon along the jet axis is suggested by the "clan" sources. We argue that this acceleration, although minor, may be real and some supporting arguments come from the well known hydrodynamical considerations.

8

Microlensing and the Structure of X-ray Emitting Regions in QSOs

Jaroszyński M.

Acta Astronomica

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2002

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Vol. 52, No. 3

203--215

EN

We simulate microlensing of distant, multiply lensed quasars by stars in an intervening galaxy - lens. The calculations include the influence of the effect on the fluorescence Fe Kα lines. We use standard source models, involving accretion disks and a hot, diffuse component, which explain the presence of the lines as a result of radiation reprocessing in a cold disk. In all calculations we use cosmological and macro-lens parameters relevant to the source MG J0414+0534, a quasar where the iron line has been observed by Chandra. We investigate probability distribution for the line equivalent width of the microlensed source and find its dependence on the source model parameters. We show that the probability of a high strengthening of the line (as measured by the equivalent width) decreases sharply with the size of the emitting region. We apply the results of our simulations to the source MG J0414+0534. We find that the observed behavior of the source is not easy to reproduce with the help of the simplest disk and microlensing models. Of the models considered the best results are obtained with the disks around 107 Msolar black holes with inner edges at ≈10 gravitational radii.

9

GB2 0909+353: One of the Largest Double Radio Source

Jamrozy M., Machalski J.

Acta Astronomica

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1999

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Vol. 49, No. 2

181--188

EN

The evidences are given that the radio source GB2 0909+353 (GB2 catalogue: Machalski 1978; ICRS 2000.0 coordinates: 09 12 51.7, +35 10 10) is likely one of the largest classical doubles known, though its optical identification is not certain. Our deep VLA observations at 5 GHz did not reveal a radio core brighter than 0.5 mJy/beam at this frequency. Thus a distance to the source is evaluated using photometric - redshift estimates of the faint galaxies in the optical field. The equipartition magnetic field and energy density in the source is calculated and compared with corresponding parameters of other "giant" radio sources known, showing extremely low values of both physical parameters of the source investigated. On the other hand, the age of relativistic electrons, and the advance speed of the "hot spot" in the source are typical for much smaller and brighter 3CR sources.