ABSTRACT We present an analysis of 43 years (1972 to 2015) of spectroscopic observations of the Seyfert 1 galaxy NGC 5548. This includes 12 years of new unpublished observations (2003 to 2015). We ...compiled about 1600 Hβ spectra and analyzed the long-term spectral variations of the 5100 continuum and the Hβ line. Our analysis is based on standard procedures, including the Lomb-Scargle method, which is known to be rather limited to such heterogeneous data sets, and a new method developed specifically for this project that is more robust and reveals a ∼5700 day periodicity in the continuum light curve, the Hβ light curve, and the radial velocity curve of the red wing of the Hβ line. The data are consistent with orbital motion inside the broad emission line region of the source. We discuss several possible mechanisms that can explain this periodicity, including orbiting dusty and dust-free clouds, a binary black hole system, tidal disruption events, and the effect of an orbiting star periodically passing through an accretion disk.
ABSTRACT
We present a detailed analysis of 30 very long baseline interferometric (VLBI) observations of the BL Lac object S5 1803+784 (z= 0.679), obtained between mean observational time 1994.67 and ...2012.91 at observational frequency 15 GHz. The long-term behaviour of the jet ridge line reveals the jet experiences an oscillatory motion superposed on its helical jet kinematics on a time-scale of about 6 yr. The excess variance of the positional variability indicates the jet components being farther from the VLBI core have larger amplitude in their position variations. The fractional variability amplitude shows slight changes in 3 yrbins of the component’s position. The temporal variability in the Doppler boosting of the ridge line results in jet regions behaving as flaring ‘radio lanterns’. We offer a qualitative scenario leading to the oscillation of the jet ridge line that utilizes the orbital motion of the jet emitter black hole due to a binary black hole companion. A correlation analysis implies composite origin of the flux variability of the jet components, emerging due to possibly both the evolving jet structure and its intrinsic variability.
Aims. We aim to unveil the most massive central cluster black holes in the Universe. Methods. We present a new search strategy, which is based on a black hole mass gain sensitive calorimeter and ...which links the innermost stellar density profile of a galaxy to the adiabatic growth of its central supermassive black hole (SMBH). As a first step we convert observationally inferred feedback powers into SMBH growth rates using reasonable energy conversion efficiency parameters, ϵ. In the main part of this paper we use these black hole growth rates, sorted in logarithmically increasing steps encompassing our whole parameter space, to conduct N-body computations of brightest cluster galaxies (BCGs) with the newly developed Muesli software. For the initial setup of galaxies, we use core-Sérsic models to account for SMBH scouring. Results. We find that adiabatically driven core regrowth is significant at the highest accretion rates. As a result, the most massive black holes should be located in BCGs with less pronounced cores when compared to the predictions of empirical scaling relations, which are usually calibrated in less extreme environments. For efficiency parameters ϵ< 0.1, BCGs in the most massive, relaxed, and X-ray luminous galaxy clusters might even develop steeply rising density cusps. Finally, we discuss several promising candidates for follow-up investigations, among them the nuclear black hole in the Phoenix cluster. Based on our results, its central black hole might have a mass of the order of 1011 M⊙.
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A swirling jet in the quasar 1308+326 Britzen, S.; Qian, S.-J.; Steffen, W. ...
Astronomy and astrophysics (Berlin),
06/2017, Volume:
602
Journal Article
Peer reviewed
Open access
Context. Despite numerous and detailed studies of the jets of active galactic nuclei (AGN) on pc-scales, many questions are still debated. The physical nature of the jet components is one of the most ...prominent unsolved problems, as is the launching mechanism of jets in AGN. The quasar 1308+326 (z = 0.997) allows us to study the overall properties of its jet in detail and to derive a more physical understanding of the nature and origin of jets in general. The long-term data provided by the Monitoring Of Jets in Active galactic nuclei with Very Long Baseline Array (VLBA) experiments (MOJAVE)⋆⋆ survey permit us to trace out the structural changes in 1308+326 that we present here. The long-lived jet features in this source can be followed for about two decades. Aims. We investigate the very long baseline interferomety (VLBI) morphology and kinematics of the jet of 1308+326 to understand the physical nature of this jet and jets in general, the role of magnetic fields, and the causal connection between jet features and the launching process. Methods. Fifty VLBA observations performed at 15 GHz from the MOJAVE survey were re-modeled with Gaussian components and re-analyzed (the time covered: 20 Jan. 1995–25 Jan. 2014). The analysis was supplemented by multi-wavelength radio-data (UMRAO, at 4.8, 8.0, and 14.5 GHz) in polarization and total intensity. We fit the apparent motion of the jet features with the help of a model of a precessing nozzle. Results. The jet features seem to be emitted with varying viewing angles and launched into an ejection cone. Tracing the component paths yields evidence for rotational motion. Radio flux-density variability can be explained as a consequence of enhanced Doppler boosting corresponding to the motion of the jet relative to the line of sight. Based on the presented kinematics and other indicators, such as electric-vector polarization position-angle (EVPA) rotation, we conclude that the jet of 1308+326 has a helical structure, meaning that the components are moving along helical trajectories and the trajectories themselves are also experiencing a precessing motion. A model of a precessing nozzle was applied to the data and a subset of the observed jet feature paths can be modeled successfully within this model. The data till 2012 are consistent with a swing period of 16.9 yr. We discuss several scenarios to explain the observed motion phenomena, including a binary black hole model. It seems unlikely that the accretion disk around the primary black hole, which is disturbed by the tidal forces of the secondary black hole, is able to launch a persistent axisymmetric jet. Conclusions. We conclude that we are observing a rotating helix. In particular, the observed EVPA swings can be explained by a shock moving through a straight jet that is pervaded by a helical magnetic field. We compare our results for 1308+326 with other astrophysical scenarios where similar, wound-up filamentary structures are found. They are all related to accretion-driven processes. A helically moving or wound up object is often explained by filamentary features moving along magnetic field lines of magnetic flux tubes. It seems that a “component” comprises plasma tracing the magnetic field, which guides the motion of the radiating radio-band plasma. Further investigations and modeling are in preparation.
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We investigate the pc-scale kinematics and kpc-scale radio morphology of the quasar PG 1302–102, which may harbour a sub-pc separation supermassive binary black hole system at its centre as inferred ...from optical variability. High-resolution radio interferometric measurements obtained with the Very Long Baseline Array (VLBA) in the Monitoring Of Jets in Active galactic nuclei with VLBA Experiments programme at 15 GHz at 20 epochs spanning 17 years were analysed to investigate the pc-scale radio structure. Archival observations with the Very Large Array at 1.4 and 5 GHz were obtained to study the kpc-scale morphology. We find that the pc-scale jet is inclined within ∼2
$_{.}^{\circ}$
2 to the line of sight and has a half-opening angle of ∼0
$_{.}^{\circ}$
2. The parameters derived from the pc-scale radio jet are qualitatively consistent with those obtained from the analysis of the optical light curve of PG 1302–102. We obtain at least 0.08 for the mass ratio of the two black holes in the system. We find some indication for a helical jet structure on kpc-scale, but the directions of the inner and the extended radio jets are significantly different, obstructing a straightforward connection of the pc- and kpc-scale jets within the binary scenario.
Abstract
We present the analysis of near-infrared (NIR), adaptive optics Subaru and archived
HST
imaging data of a region near the northern middle lobe of the Centaurus A (Cen A) jet, at a distance ...of ∼15 kpc northeast from the center of NGC5128. Low-pass filtering of the NIR images reveals a strong—
above the background mean—signal at the expected position of the brightest star in the equivalent
HST
field. Statistical analysis of the NIR background noise suggests that the probability to observe a
signal at the same position, in three independent measurements due to stochastic background fluctuations alone is negligible (
) and, therefore, that this signal should reflect the detection of the NIR counterparts of the brightest
HST
star. An extensive photometric analysis of this star yields
V
−
I
, visual–NIR, and NIR colors expected from a yellow supergiant with an estimated age
Myr. Furthermore, the second and third brighter
HST
stars are, likely, also supergiants in Cen A, with estimated ages
Myr and
Myr, respectively. The ages of these three supergiants are in good agreement with the ages of the young massive stars that were previously found in the vicinity and are thought to have formed during the later phases of the jet-H
i
cloud interaction that appears to drive the star formation in the region for the past ∼100 Myr.
“Black Holes in a Violent Universe” is a COST Action (MP0905) connecting scientists from different disciplines – astronomers from all wavelength regimes (i.e. radio to TeV), physicists and particle ...physicists, theoreticians and observers – from currently 25 countries. The aim is to collaborate in a cross-disciplinary and multi-dimensional approach towards a better understanding of the general Black Hole phenomenon. COST (European Cooperation in Science and Technology) is one of the longest-running European instruments supporting cooperation among scientists and researchers across Europe. The goal of MP0905 is to decipher further the way the Universe and the stars and galaxies evolved and – in particular – the role Black Holes play in this. This Action is an open and flexible program of communication and interchange.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Context. The search for periodic features in flux variability and kinematics of superluminal components in blazars is capable of providing significant clues for the understanding of the physical ...processes in their central engines (black-hole/accretion-disk systems), especially concerning the formation and structure of their relativistic jets and radiation mechanisms. Aims. The jet swing on parsec-scales and the change of the ejection position angle of the superluminal components with time in the quasar B1308+326 (z = 0.997) are investigated as quasi-periodic behaviors. Methods. A previously published precessing jet nozzle model is applied to model the source kinematics and a possible jet precession period is found. Results. Based on the model fitting of the kinematics for a subset of components, it is shown that their kinematics, including the shape of the inner trajectories and the motion of the components, could be well fitted in terms of the precessing jet nozzle model and a precession period of ~16.9 ± 0.3 yr is derived. Different precession mechanisms are discussed and compared. Conclusions. It is shown that the swing of the ejection position angle of the superluminal knots observed in B1308+326 may be due to the orbital motion of a putative supermassive black hole binary in its nucleus. Some relevant parameters of the binary model are estimated. We also discuss the spin-induced precession mechanism in the single black hole scenario and an estimate for the spin of the Kerr black hole is obtained.
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NGC 3718 is a low-ionization nuclear emission line region (LINER) L1.9 galaxy, lying at a distance of about ~17.4 Mpc from the Earth; its similarities with NGC 5128 often award it the name northern ...Centaurus A. The presence of a compact radio source with a candidate jet structure, a prominent dust lane, and a strongly warped molecular and atomic gas disk are indications that NGC 3718 has undergone some sort of a large-scale gravitational interaction sometime in the recent past, which channeled gas towards the center, feeding the black hole and igniting the central engine. The characteristics combined with the observed spatial NIR and radio emission offsets, the relative redshift between the broad and the narrow Halpha line, the limited star formation activity, and AGN feedback strongly imply the existence of a super-massive black hole recoil. Finally, we discuss a possible interpretation that could naturally incorporate all these findings into one physically consistent picture.
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If we assume that nuclei of extragalactic radio sources contain binary black hole systems, the two black holes can eject VLBI components, in which case two families of different VLBI trajectories ...will be observed. Another important consequence of a binary black hole system is that the VLBI core is associated with one black hole, and if a VLBI component is ejected by the second black hole, one expects to be able to detect the offset of the origin of the VLBI component ejected by the black hole that is not associated with the VLBI core. The ejection of VLBI components is perturbed by the precession of the accretion disk and the motion of the black holes around the center of gravity of the binary black hole system. We modeled the ejection of the component taking into account the two pertubations and present a method to fit the coordinates of a VLBI component and to deduce the characteristics of the binary black hole system. Specifically, this is the ratio Tp/Tb where Tp is the precession period of the accretion disk and Tb is the orbital period of the binary black hole system, the mass ratio M1/M2, and the radius of the binary black hole system Rbin. From the variations of the coordinates as a function of time of the ejected VLBI component, we estimated the inclination angle io and the bulk Lorentz factor γ of the modeled component. We applied the method to component S1 of 1823+568 and to component C5 of 3C 279, which presents a large offset of the space origin from the VLBI core. We found that 1823+568 contains a binary black hole system whose size is Rbin ≈ 60 μas (μas is a microarcsecond) and 3C 279 contains a binary black hole system whose size is Rbin ≈ 420 μas. We calculated the separation of the two black holes and the coordinates of the second black hole from the VLBI core. This information will be important to link the radio reference-frame system obtained from VLBI observations and the optical reference-frame system obtained from Gaia.
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