113 research outputs found
Compact jets as probes for sub-parsec scale regions in AGN
Compact relativistic jets in active galactic nuclei offer an effective tool
for investigating the physics of nuclear regions in galaxies. The emission
properties, dynamics, and evolution of jets in AGN are closely connected to the
characteristics of the central supermassive black hole, accretion disk and
broad-line region in active galaxies. Recent results from studies of the
nuclear regions in several active galaxies with prominent outflows are reviewed
in this contribution.Comment: AASLaTeX, 5 pages, 4 figures. Accepted in Astrophysics and Space
Scienc
Evidence that the Bursting Component of the X-ray Radiation From 3C 111 Originates in the PC-Scale Jet
Evidence is presented indicating that the bursting component of the X-ray
radiation detected in the nuclear region of the active radio galaxy 3C 111
comes from the blobs ejected in the pc-scale jet and not from the accretion
disc. After each new outburst the radio flux density associated with it
increases to a peak in ~1 year and then subsides over a period of 1-2 years
with the flux falling off exponentially as the blob moves outward and
dissipates. Similar peaks (bursts) are seen in the X-ray light curve and a
cross-correlation between the two shows a very high correlation with the X-ray
peaks leading the radio peaks by ~100 days. A second cross-correlation, this
time between the radio event start times and the X-ray light curve, also shows
a significant correlation. When this is taken together with the long (~1 yr)
delay between the start of each ejection event and its associated X-ray peak it
indicates that this bursting component of the X-ray flux must be associated
with the ejected blobs in the pc-scale jet and not with the accretion disc.
Because X-ray telescopes do not have the resolution required to resolve the
accretion disc area from the pc-scale jet, this paper is the first to present
observational evidence that can pinpoint the point of origin of at least those
long-timescale X-ray bursts with durations of 1-3 yrs.Comment: 11 pages, 8 Figures. Accepted for publication in Astrophysics and
Space Scienc
Extragalactic Relativistic Jets and Nuclear Regions in Galaxies
Past years have brought an increasingly wider recognition of the ubiquity of
relativistic outflows (jets) in galactic nuclei, which has turned jets into an
effective tool for investigating the physics of nuclear regions in galaxies. A
brief summary is given here of recent results from studies of jets and nuclear
regions in several active galaxies with prominent outflows.Comment: 5 pages; contribution to ESO Astrophysical Symposia, "Relativistic
Astrophysics and Cosmology", eds. B. Aschenbach, V. Burwitz, G. Hasinger, B.
Leibundgut (Springer: Heidelberg 2006
Polarimetric Observations of 15 AGNs at High Frequencies
Original paper can be found at: http://www.astrosociety.org/pubs/cs/328.html--Copyright Astronomical Society of the PacificWe have obtained total and polarized intensity images of 15 AGNs with the VLBA at 7 mm at 17 epochs from 25/26 March 1998 to 14 April 2001. The VLBA observations are accompanied at many epochs by simultaneous mea- surements of polarization at 1.35/0.85 mm as well as less frequent simultaneous optical polarization measurements. We discuss the similarities and complexities of polarization behavior at different frequencies along with the VLBI properties
Behaviour of the Blazar CTA 102 during two giant outbursts
Blazar CTA 102 underwent exceptional optical and high-energy outbursts in 2012 and 2016-2017. We analyze its behaviour during these events, focusing on polarimetry as a tool that allows us to trace changes in the physical conditions and geometric configuration of the emission source close to the central black hole. We also use Fermi gamma-ray data in conjunction with optical photometry in an effort to localize the origin of the outbursts.AST-1615796 - Boston Universit
Probing the innermost regions of AGN jets and their magnetic fields with radioastron. I. Imaging BL LACERTAE at 21 μm as resolution
We present the first polarimetric space very long baseline interferometry (VLBI) imaging observations at 22 GHz. BL Lacertae was observed in 2013 November 10 with the RadioAstron space VLBI mission, including a ground array of 15 radio telescopes. The instrumental polarization of the space radio telescope is found to be less than 9%, demonstrating the polarimetric imaging capabilities of RadioAstron at 22 GHz. Ground-space fringes were obtained up to a projected baseline distance of 7.9 Earth diameters in length, allowing us to image the jet in BL Lacertae with a maximum angular resolution of 21 μas, the highest achieved to date. We find evidence for emission upstream of the radio core, which may correspond to a recollimation shock at about 40 μas from the jet apex, in a pattern that includes other recollimation shocks at approximately 100 and 250 μas from the jet apex. Polarized emission is detected in two components within the innermost 0.5 mas from the core, as well as in some knots 3 mas downstream. Faraday rotation analysis, obtained from combining RadioAstron 22 GHz and ground-based 15 and 43 GHz images, shows a gradient in rotation measure and Faraday-corrected polarization vector as a function of position angle with respect to the core, suggesting that the jet in BL Lacertae is threaded by a helical magnetic field. The intrinsic de-boosted brightness temperature in the unresolved core exceeds K, suggesting, at the very least, departure from equipartition of energy between the magnetic field and radiating particles.This research has been supported by the Spanish Ministry of Economy and Competitiveness grant AYA2013-40825-P, by the Russian Foundation for Basic Research (projects 13-02-12103, 14-02-31789, and 15-02-00949), and St. Petersburg University research grant 6.38.335.2015. The research at Boston University (BU) was funded in part by NASA Fermi Guest Investigator grant NNX14AQ58G. Y.M. acknowledges support from the ERC Synergy Grant >BlackHoleCam-Imaging the Event Horizon of Black Holes> (Grant 610058). Part of this work was supported by the COST Action MP1104 >Polarization as a tool to study the Solar System and beyond.> The RadioAstron project is led by the Astro Space Center of the Lebedev Physical Institute of the Russian Academy of Sciences and the Lavochkin Scientific and Production Association under a contract with the Russian Federal Space Agency, in collaboration with partner organizations in Russia and other countries.Peer Reviewe
THE CONNECTION between the RADIO JET and the GAMMA-RAY EMISSION in the RADIO GALAXY 3C 120
© 2015. The American Astronomical Society. All rights reserved. We present the analysis of the radio jet evolution of the radio galaxy 3C 120 during a period of prolonged γ-ray activity detected by the Fermi satellite between 2012 December and 2014 October. We find a clear connection between the γ-ray and radio emission, such that every period of γ-ray activity is accompanied by the flaring of the millimeter very long baseline interferometry (VLBI) core and subsequent ejection of a new superluminal component. However, not all ejections of components are associated with γ-ray events detectable by Fermi. Clear γ-ray detections are obtained only when components are moving in a direction closer to our line of sight. This suggests that the observed γ-ray emission depends not only on the interaction of moving components with the millimeter VLBI core, but also on their orientation with respect to the observer. Timing of the γ-ray detections and ejection of superluminal components locate the γ-ray production to within ∼0.13 pc from the millimeter VLBI core, which was previously estimated to lie about 0.24 pc from the central black hole. This corresponds to about twice the estimated extension of the broad line region, limiting the external photon field and therefore suggesting synchrotron self Compton as the most probable mechanism for the production of the γ-ray emission. Alternatively, the interaction of components with the jet sheath can provide the necessary photon field to produced the observed γ-rays by Compton scattering.his research has been supported by the Spanish Ministry of Science and Innovation grants AYA2010-14844, and AYA2013-40825 P, and by the Regional Government of Andalucia (Spain) grant P09-FQM-4784. This research was partly supported by the Russian Foundation for Basic Research grant 13-02-12103 and by the Academy of Finland project 274477.Peer Reviewe
Changes in the trajectory of the radio jet in 0735+178?
We present multi-epoch 8.4 and 43 GHz Very Long Baseline Array images of the
BL Lac object 0735+178. The images confirm the presence of a twisted jet with
two sharp apparent bends of 90 within two milliarcseconds of the
core, resembling a helix in projection. The observed twisted geometry could be
the result of precession of the jet inlet, but is more likely produced by
pressure gradients in the external medium through which the jet propagates.
Quasi-stationary components are observed at the locations of the 90
bends, possibly produced by differential Doppler boosting. Identification of
components across epochs, since the earliest VLBI observations of this source
in 1979.2, proves difficult due to the sometimes large time gaps between
observations. One possible identification suggests the existence of
superluminal components following non--ballistic trajectories with velocities
up to . However, in images obtained after mid-1995,
components show a remarkable tendency to cluster near several jet positions,
suggesting a different scenario in which components have remained nearly
stationary in time at least since mid-1995. Comparison with the earlier
published data, covering more than 19 years of observations, suggests a
striking qualitative change in the jet trajectory sometime between mid-1992 and
mid-1995, with the twisted jet structure with stationary components becoming
apparent only at the later epochs. This would require a re-evaluation of the
physical parameters estimated for 0735+178, such as the observing viewing
angle, the plasma bulk Lorentz factor, and those deduced from these.Comment: 18 pages, 5 figures, accepted for publication in MNRA
Large Kinetic Power in FRII Radio Jets
We investigate the total kinetic powers (L_{j}) and ages (t_{age}) of
powerful jets of four FR II radio sources (Cygnus A, 3C 223, 3C 284, and 3C
219) by the detail comparison of the dynamical model of expanding cocoons with
observed ones. It is found that these sources have quite large kinetic powers
with the ratio of L_{j} to the Eddington luminosity (L_{Edd}) resides in . Reflecting the large kinetic powers, we also find that the
total energy stored in the cocoon (E_{c}) exceed the energy derived from the
minimum energy condition (E_{min}): . This implies that
a large amount of kinetic power is carried by invisible components such as
thermal leptons (electron and positron) and/or protons.Comment: 5 pages, accepted for publication in Astrophysics and Space Scienc
The Point of Origin of the Radio Radiation from the Unresolved Cores of Radio-Loud Quasars
Locating the exact point of origin of the core radiation in active galactic
nuclei (AGN) would represent important progress in our understanding of
physical processes in the central engine of these objects. However, due to our
inability to resolve the region containing both the central compact object and
the jet base, this has so far been difficult. Here, using an analysis in which
the lack of resolution does not play a significant role, we demonstrate that it
may be impossible even in most radio loud sources for more than a small
percentage of the core radiation at radio wavelengths to come from the jet
base. We find for 3C279 that percent of the core flux at 15 GHz must
come from a separate, reasonably stable, region that is not part of the jet
base, and that then likely radiates at least quasi-isotropically and is
centered on the black hole. The long-term stability of this component also
suggests that it may originate in a region that extends over many Schwarzschild
radii.Comment: 7 pages with 3 figures, accepted for publication in Astrophysics and
Space Scienc
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