POSTER ABSTRACTS
POSTERS
The Water Vapour Radiometer at Effelsberg
A.L. Roy, U. Teuber, R. Keller, H. Rottmann We have installed a scanning 18 GHz to 26 GHz water vapour radiometer on the focus cabin of Effelsberg 100 m telescope for correction of tropospheric phase, delay and opacity variations during high-frequency VLBI observations. The radiometer has been found to improve the phase coherence of 3 mm VLBI data, enhancing the sensitivity by a factor up to two. We describe the radiometer and show results from validation tests.
Observational evidence for the link between the compact jet and optical continuum in the radio galaxy 3C 390.3
T.G. Arshakian, A.P. Lobanov, V.H. Chavushyan, A.I. Shapovalova, J.A.Zensus The “central engine” of AGN is thought to be powered by accretion on a central nucleus believed to be a super-massive black hole. The localization and exact mechanism of the energy release in AGN are still not well understood. We present observational evidence for the link between variability of the radio emission of the compact jet, optical and X-ray continua emission and ejections of new jet components in the radio galaxy 3C 390.3. These correlations indicate that the source of variable non-thermal continuum radiation is located in the innermost part of the relativistic jet. We suggest that the continuum emission from the jet and counterjet ionizes material in a subrelativistic outflow surrounding the jet, which results in a formation of two conical regions with broad emission lines (in addition to the conventional broad line region around the central nucleus) at a distance more than or equal to 0.4 parsecs from the central engine.
Radio-optical scrutiny of
the central engine in compact AGN
T.G. Arshakian, V.H. Chavushyan, E. Ros, A.P. Lobanov, J.A. Zensus, M.
Kadler
The exact mechanism of energy release and its location in the AGN, the
empirical relations between the central engine and the relativistic jet,
and the physical processes behind these relations are still poorly
understood, partly because they operate close to the BH within the central
light year, at sub-milliarcsecond angles from Earth.
The VLBI technique provides unparalleled resolution with which to observe
the jets at sub-milliarcsecond scales, corresponding to pc-scales. Since
1994, the Very Long Baseline Array (VLBA) has conducted an extensive
series of multi-epoch imaging at 15 GHz (known as 2 cm and MOJAVE surveys
[1,2,3]) with which one can measure kinematics, polarization and magnetic
field structure of relativistic pc-scale jets.
The optical continuum and emission line characteristics of AGN may provide
valuable information on the properties of the central BH and dynamics of
the surrounding environment, sub-pc-scale broad-emission-line region and
the kpc-scale narrow-emission-line region.
A combination of sub-milliarcsecond resolution very long baseline
interferometry (VLBI) radio observations of the jets and optical
spectroscopy of nuclear regions in the host galaxies can provide key
evidence for identifying the structure and dynamics and exact radiation
mechanisms operating in the innermost of the pc-scale region – the central
engine of AGN.
Towards a kinematic model of the Local Group
A. Brunthaler, M.J. Reid, A. Loeb, H. Falcke, L.J. Greenhill, C. Henkel
Key and still largely missing parameters for measuring the matter
content and distribution of the Local Group are the proper motion
vectors of its member galaxies. Very Long Baseline Interferometry (VLBI)
observations of bright H$_2$O masers in M33 enabled us to measure the
3-D motion of this galaxy relative to the Milky Way of 190 $\pm$ 59 km
s$^{-1}$. This measurement severely constrains the
possible values of M31's proper motion. The condition that M33's stellar
disk will not be tidally disrupted by either M31 or the Milky Way over
the past 10 billion years, favors a proper motion amplitude of
100 $\pm$ 20 km s$^{-1}$ for M31.
Present and future mm-VLBI imaging of jets in AGN: the case of NRAO 150
I. Agudo, T.P. Krichbaum, U. Bach, A. Pagels, D. Graham, W. Alef, A. Witzel, J.A. Zensus, M. Bremer, M. Grewing
The Global mm--VLBI Array is at present the most
sensitive 3\,mm--VLBI interferometer and provides images
of up to 40 micro--arcsecond resolution.
Using this array, we have monitored the rotation of the innermost
jet in the quasar NRAO\,150, which shows an angular speed of
$\sim 7^{\circ}/\rm{yr}$.
Future 3\,mm arrays could include additional stations like
ALMA, GBT, LMT, CARMA, SRT, Yebes, Nobeyama and Noto, which
would allow to push VLBI at this wavelength to sensitivity
and image quality levels comparable to those of present VLBI
at centimeter wavelengths.
This would improve our knowledge of the accretion systems
and the magneto--hydrodynamics of the innermost jets in AGN.
Multi-Frequency VLBI Observations of Gravitational Lens B2016+112
A. Moré, R. Porcas, M. Garrett, S. Nair
We present GLOBAL VLBI images of the gravitational lens B2016+112 at 18 and 6 cm. Previous observations revealed that the lensed images A, B and C each are divided into sub-components. With the help of the high resolution maps, we could determine the spectra of each of these sub-components and compare them with the most recent Koopmans et al. (2002) model. The spectra of the outermost two sub-components, in the arc-like C component, are not similar. Possible reasons for these could be free-free absorption along the line of sight to one of the images or presence of substructure.
Foreground radio sources in the CBI fields
E. Angelakis, A. Kraus, A. C. S. Readhead, R. Bustos, T. P. Krichbaum, T. J. Pearson, A. Witzel, A. J. Zensus
In the context of the current project a significant number of ~6000 extragalactic radio sources are observed at 2 frequencies quasi-simultaneously with the 100-meter radio telescope in Effelsberg. The sample is extracted from the NVSS catalog and consists of all the radio sources brighter than 2.5 mJy that happen to be in the fields targeted by the CBI experiment. The motivation for that is to study their spectra and from that to identify those that should be "vetoed out" from the CBI data since they may be causing severe contamination. However, being such an extended sample it can also serve as an excellent basis for reliable radio sources statistics and more.
Continuum EVN and MERLIN observations of Ultra Luminous Infrared Galaxies
A.G. Polatidis, J.E. Conway, Y. Pihlström
Radio imaging of Ultra Luminous Infrared galaxies (ULIRG) is ideal to explore the connection between the starburst and the AGN phenomenon since it is unaffected by dust obscuration. We have made combined 18cm radio continuum, EVN and MERLIN observations of 13 ULIRGs that have the parsec and deci-parsec scale resolution necessary to distinguish between an AGN and radio supernovae or supernovae remnants at the centres of these galaxies, and assess the contribution of each to the total energy distribution. In the brightest ULIRGs discussed in this poster, 50% to 70% of the total flux density is resolved out at parsec scale resolution. Their parsec scale structure consists of multiple components with sizes of a few to tens of parsecs, brightness temperatures ranging from 105 K to 107 K and luminosities from 1037 erg/s to 1040 erg/s (UGC 05101). All components are too large to be single radio supernovae and their luminosities are a few thousand times brighter than Cas A but similar to the supernova 1989J. It is therefore possible that at least some of these components are clustered young radio supernovae (RSN) or supernovae remnants. However the high brightness temperature parsec scale emission is due to an AGN, in particular in UGC 05101 whose components are much more luminous than 1989J. This plausibility is further supported from the detection of iron lines in X-ray observations.
K.É. Gabányi, S. Britzen, T.P. Krichbaum, U. Bach, L. Fuhrmann, A. Kraus, A.
Witzel, J.A. Zensus
In radio bands, the study of compact radio sources could be affected by
propagation
effects. These are usually attributed to the presence of turbulent
intervening
material along the line of sight. In this poster, two of such effects are
presented.
The line of sight of B2005+403 passes through the heavily scattered region
of Cygnus,
which causes substantial angular broadening of the source image between 0.6
GHz
and 8 GHz. At higher frequencies however the intrinsic source structure
shines
through. Therefore multi-frequency VLBI observations allows us, to study the
characteristics of the intervening material, the source morphology and the
"coupling" of them in forming the observed image.
J1128+592 is a newly found relatively fast IDV source. At present the mixing
ratio between source intrinsic and source extrinsic IDV is unclear. One of
the
strongest evidence in favor of propagation induced IDV is the annual
modulation
of the observed variability timescale. As the Earth orbits around the Sun,
the
relative velocity between the observer and the scattering material changes,
causing slow down and speeding up of the variations in different time of the
year. So far, the observations of J1128+592 suggest that the changes of its
variability timescale can be attributed to annual modulation.
Fluid instabilities in relativisitc jets. Comparison between analytical and numerical approaches.
M. Perucho, A.P. Lobanov, J.Mª Martí
Relativistic outflows represent one of the best-suited tools to probe the physics of AGN. Numerical modellingof internal structure of the relativistic outflows on parsec scales provides important clues about the conditions and dynamics of the material in the immediate vicinity of the central black holes in AGN. We investigate possible causes of the structural patterns and regularities observed in the parsec-scale jet of the well-known quasar 3C 273. We present here the results from a 3D relativistic hydrodynamics numerical simulation in which we include jet precession and component injection. We compare the model with the structures observed in 3C 273 using very long baseline interferometryand constrain the basic properties of the flow. Our results show that matching accurately the model and observedstructures requires smaller viewing angle of the jet than previously thought, thereby alleviating the constraints on the kinetic power and energy content of the jet.
A Global 86 GHz VLBI Survey of Compact Radio Sources
S.-S. Lee, A.P. Lobanov, T.P. Krichbaum, A. Witzel, J.A. Zensus
A new global VLBI(Very Long Baseline Interferometry) survey of compact radio sources at 86 GHz has been started in October 2001. Its main aim was to increase the total number of objects accessible for future 3mm-VLBI imaging by a fact of 3~5. The participation of large and sensitive European antennas (like the 100m RT at Effelsberg, the 30m MRT at Pico Veleta, the 6x15m interferometer on Plateau de Bure) provides a single baseline sensitivity of up to ~ 0.1Jy, an image sensitivity of better than 10 mJy/beam, and a global uv-coverage for each source. In combination with European antennas (Onsala, Metsahovi) and the VLBA, the survey will be more sensitive and contain more sources than previous 3mm-surveys (i.e. Londsdale et al. 1998, Lobanov et al. 2000). The survey was conducted in 3 observing session (October 2001, April 2002 and October 2002). A total of 127 compact radio sources selected on the basis of their flux density and northern declination was observed. Out of 127 sources, 92 sources are now fringe-fitted, calibrated and mapped. The rest sources are fringe-fitted, calibrated and ready to be mapped. Among a total of 127 sources observed, only 5 sources (0710+439, 3C309.1, 1749+701, 2021+614, MWC 349) are not detected, and 13 sources are not able to be imaged due to insufficient uv-coverages. So, totally 109 sources are expected to be imaged. For those 109 sources, the flux densities and sizes of core and jet components will be measured using Gaussian modelfitting within the DIFMAP program. The component sizes and flux densities lead to brightness temperature estimates for each structure component. A preliminary result is the correlation of the brightness temperature of the jet components with their apparent jet speed (jet speed measured at longer wavelengths).
VLBI Polarisation Observations of Intraday Variability
C. M. V. Impellizzeri, S. Bernhart, T. P. Krichbaum, U. Bach, L. Fuhrmann, A. Kraus, S. Britzen, A. Witzel, J. A. Zensus
Extragalactic, flat specrtum sources are known to be highly variable, about 30% of them show intraday variability (IDV). Recently, IDV has been explained in terms of refractive interstellar scintillation (RISS) in the interstellar medium of our galaxy, but some effects remain that are likely to be caused by source-intrinsic relativistic jet-physics. Both scenarios require the existence of ultra-compact emission regions in the source itself. We used the VLBI to image well known fast variable sources on IDV timescales, i.e. few days to hours, in total and polarized flux density. From our observations we found that all our IDV sources area core-dominated and are likely to be highly beamed. Moreover, where variations took place these could be uniquely associated with the innermost, unresolved core region, and not with the extened jet, however to a scale that was smaller than our VLBA beam indicating that the variable region is very compact and giving an upper limit to the size of this region.
R. Mittal, R. Porcas
We present the results of phase{referenced
VLBA+E
elsberg observations at ve frequencies of the double-image gravitational
lens
JVAS B0218+357, made to establish the precise registration of the
A and B lensed image positions. The motivation behind these observations
is to investigate the anomalous variation of the image flux-
density ratio (A/B) with frequency - this ratio changes by almost a
factor of two over a frequency range from 1.65 GHz to 15.35 GHz. We
investigate whether frequency dependent image positions, combined
with a magnification gradient across the image field, could give rise to
the anomaly. Our observations confirm the variation of image flux-
density ratio with frequency. The results from our phase-reference
astrometry,
taken together with the lens mass model of Wucknitz (2002)
show that shifts of the image peaks and centroids are too small to account
for the observed frequency-dependent ratio.
Space VLBI studies of extragalactic jets
A.P. Lobanov, J.A. Zensus, T.P. Krichbaum, A. Witzel
The VLBI Space Observatory Programme (VSOP) has been the most successful space VLBI effort so far. Exemplified here are the superb capabilities of the VSOP for imaging compact radio sources and studying in detail internal structure and physical properties of extragalactic jets. Internal structure of the parsec-scale jet in the well-known quasar 3C273 uncovered by the VSOP observations at 5 GHz has enabled the most detailed determination of basic physicsal properies of the flow to be made. In the distant quasar 0836+710, matching resolutions of the space VLBI observations at 1.6 GHz and ground VLBI observations at 5 GHz has made it possible to obtained the most detailed spectral index image to date. Both images provide a wealth of information for studying intricate physics of relativistic flows.
Binary supermassive black holes driving AGN activity
A.P. Lobanov
Nuclear activity in galaxies believed to result from accretion onto supermassive black holes (SMBH) is a complex phenomenon regulated by a number of factors. It is widely recognized that the nuclear activity is closely connected to galactic mergers. A merger has two most immediate effects on the environment of SMBH residing in the galactic nuclei: (i)~it perturbs substantially the dynamics of gas and stellar population in the merging galaxies, and (ii)~it leads to formation of supermassive binary black holes (BBH) in the center of mass of the two galaxies merged. The poster discusses the influence of dynamic evolution of the BBH on the nuclear activity. The peak magnitude of the nuclear activity is shown to be connected with the primary parameters of a BBH system: the mass ratio and orbital separation of the two black holes. The scheme predicts correctly the relative fractions of different types of active galactic nuclei (AGN) and explains the connection between the galactic type and the strength of the nuclear activity. It shows that most powerful AGN should result from mergers with small mass ratios, while weaker nuclear activity is produced in unequal mergers.
A rotating helix in S5 1803+784
S. Britzen, N.A. Kudzyavtseva, E. Ros, A. Witzel
The blazar S5 1803+784 has been observed with VLBI at ?=1.6, 2.3, 5, 15 and 43 GHz (Marcaide et al. 1985, Guirado et al. 2001, Gurvits et al., Perez-Torres et al. 2000, Ros et al. 2000, 2001 and Kellermann et al. 1998) during the years 1993 - 2002. We made Gaussian modelfits for these datasets and found that the jet structure could be described with a number of stationary jet components. The most suitable model for S5 1803+784 capable of explaining these observations is a rotating helix.
