ABSTRACTS
High Energy Blazar Astronomy
Tuorla Observatory, Finland, 17-21 June 2002
Abstracts will be placed on this page (totally unmodified) twice or
thrice a week as they are received along with the registrations.
Here are what we have so far:
3C345: A precessing jet?
(Contributed talk)
Zulema Abraham, Anderson Caproni
IAG, University of São Paulo, Brasil
VLBI observations of 3C345 during the last 25 years showed a
considerable number of superluminal components moving along
curved paths with variable velocities. These motions were
interpreted as helical paths, due probably to jet precession.
In our work we show that the available data are also
consistent with ballistic motion for the jet components,
with different velocities and position angles in the plane
of the sky for each one of them. We interpreted these results
in terms of a precessing jet model, with constant Lorentz
factor for the jet bulk motion, in which the differences is
superluminal velocities are attributed to differences in the
angle between the jet, when the component was formed, and the
line of sight. We determined the model parameters: precession
period, Lorentz factor, aperture of the precessing cone and
angle between the cone axis and the line of sight. The
precession period we obtained coincides with one of the
periods found in the historical optical light curve.
We identified the epoch of formation of each superluminal
component with the occurrence of a short lived optical flare
and found a correlation between the flare flux density at
optical wavelengths and the half life of the component,
measured at radio frequencies. Finally we give limits to the
masses of the black holes in the binary system assumed to be
responsible for the jet precession.
Long-term optical monitoring of 3C 66A in S.-Petersburg
University
(Poster)
M.K.Babadzhanyants and E.T.Belokon
Astronomical Institute of Saint-Petersburg University
The photometric B(V)-bands monitoring of blazar 3C 66A was carried in
the Astronomical Institute of S.-Petersburg University during
1974-1991. We present the results of these observations and the new
variant of the combined optical (B-band) light curve (1972-1999) of
3C 66A essentially improved by our extensive data set. Some properties
of this light curve and the dependences between the optical color
index B-V and the brightness for different time intervals are
discussed.
Ultra high frequency peaked BL Lac objects
(Contributed talk)
Volker Beckmann
INTEGRAL Science Data Centre (ISDC)
The unification of the BL Lac sequence is based on the observation that
the differences between radio and X-ray selected BL Lacs are due to
different peak frequencies of their synchrotron and inverse Compton
emission.
Based on the large and complete HRX-BL Lac sample, dependencies of
several physical parameters (such as luminosity, spectral shape, and
spectral energy distribution) on the synchrotron emission peak are
shown. It is also possible to explain the different evolutionary
behaviour in a unified scheme. Finally, implications on the existence
of ultra high frequency peaked BL Lac objects (UHBL) can be made.
These objects have their synchrotron peak at frequencies higher than
100 keV and make them possible targets for observations in Gamma-rays.
First encouraging results from studying UHBL candidates of the HRX-BL
Lac sample and from follow-up observations in the optical domain and
with BeppoSAX will be presented. One recently discovered UHBL is
likely to be the counterpart of an unidentified EGRET source.
The analysis of the optical variability of 3C 66A during the
state of moderate activity
(Poster)
E.T.Belokon and M.K.Babadzhanyants
Astronomical Institute of Saint-Petersburg University
We used the new variant of the optical (B-band) light curve of 3C 66A
cardinally improved by own extensive data set (1974-1991) to analyze
the optical variabiliity of this object during the state of its
moderate activity (1972-1992). In this time interval we did not find
any obvious evidence for the presence of the 65-day period revealed
by Lainela et al. (1999) in the light variations observed during the
bright state of 3C 66A (the extensive outburst occured in 1993-1997).
In the same time a nearly 900-day period may be suspected for the
state of moderate activity of this object.
Optically Identifying High Energy Gamma-Ray Sources
(Poster)
Steven D. Bloom
Hampden-Sydney College
We present an update to our study of the fields of unidentified EGRET
sources at mid to high Galactic latitude. In particular we focus on
those sources with arcsecond radio positions, so that we may follow-up
with optical indentification and monitoring. We show that several
sources have compelling candidate counterparts, and may be blazars. The
yield of such studies shows promise for these surveys in the AGILE and
GLAST eras.
Recent X-ray observations of BL Lacs
(Invited talk)
W. Brinkmann
MPE Garching
Optical Spectroscopy of BL Lac Objects: new redshifts and an
emission/absorption line study.
(Contributed talk)
N. Carangelo, R. Falomo, J. K. Kotilainen, A. Treves and M.H.
Ulrich
Universita di Milano-Bicocca
We present optical spectroscopy at intermediate resolution of ~ 30 BL
Lac Objects. The observations, gathered at the ESO 3.6m telescope equipped
with EFOSC2, are designed to derive new redshifts for sources the spectrum
of which was found featureless in previous investigations and to study the
frequency of intervening absorptions in BL Lacs. In addition we performed,
for selected nearby targets, a search for broad emission lines.
Preliminary results of this program are given together with a review of the
present knowledge of redshift information in complete samples of BL
Lacs.
Spectroscopic study of the nuclear region of blazar-like
objects
(Poster)
A.C. Goncalves & M. Serote-Roos
European Southern Observatory (Germany) & CAAUL (Lisbon)
We have examined the spectroscopic properties of a sample
of 19 optically bright, low luminosity core dominated radio
sources; this sample was expected to contain a high fraction
of objects observed at small angles to the line-of-sight.
Our study focus on the properties (stellar populations and
emission-line spectra) of such nuclei. A stellar population
synthesis shows that the populations found in these objects
are mainly composed of late-type stars, the young component
coming from supergiants. After subtraction of the stellar
contribution, we are left with a nuclear emission-line
spectra; its analysis shows that most of our objects harbour
a Low Ionization Nuclear Emission Line Region (or LINER),
whose contribution was completely swamped away by the host
galaxy starlight. In addition, the stellar populations found
are in agreement with those usually observed in LINERs.
Interaction induced activity in
Vorontsov-Vel'yaminov galaxies
(Poster)
V.P. Arkhipova1, R.I. Noskova1,
A.D. Chernin1,2
1 Sternberg Astronomical Institute, Moscow University
2 Tuorla Observatory, University of Turku
The phenomenon of AGN in interacting galaxies is studied with the
use of the dataset presented in a new extended edition of The
Catalogue of Interacting Galaxies (Vorontsov-Vel'yaminov, Arkhipova,
Noskova 2001). The total number of interacting systems in The
Catalogue is more than 2 000, and about 200 of them are found to
reveal nuclear activity. The morphological and dynamical systematics
of the galaxies with interaction induced activity is analyzed.
Synchrotron-Self Compton Spectral Evolution of PKS 2155-304
(Poster)
S. Ciprini and G. Tosti
Physics Deprtment & Astronomical Observatory, University of
Perugia
The blazar PKS 2155-304 (z=0.116) is one of the brightest and most
intensively studied prototype of BL Lac objects. Gamma-rays from PKS
2155-304 have been detected by EGRET and TeV air-shower ground
telescopes, and good X-ray observation have been collected by
satellite like ASCA, RXTE and SAX. Using simultaneous and
quasi-simultaneous multiwavelength data we computed a synchrotron
self-Compton model for the overall spectral energy distribution (SED)
and the spectral variability of this TeV source.
The optical behaviour of the blazar GC 0109+224. Hints of
Self-Organized Criticality ?
(Poster)
S. Ciprini, N. Marchili, M. Fiorucci, G. Tosti, M. Busso & G.
Nucciarelli
Physics Department & Astronomical Observatory, University
of Perugia
The observed optical luminosity of GC 0109+224 monitored at Perugia
Observatory since 1994, exhibit an intermediate behaviour between the
flickering and shot-noise, in the form of a 1/f^{alpha} noise signal.
Flares seems the sovrapposition of many peaks with hints of a sort of
self-similarity in time variability. Despite of the difficulties due
to the irregular sampling, this is preliminarly investigated.
Parametrization of Blazar Gamma-ray Emission and Implications
for the Next Generation of High-energy Space Observatories
(Poster)
A. Tramacere, S. Ciprini, M. Fiorucci, C. Cecchi & G. Tosti
Physics Department, University of Perugia & INFN Perugia
We present a parametrization for the stationary and transient
behaviour of blazar at gamma-rays energies. This has implications in
the design and development of the next generation of gamma-ray space
telescopes.
The MeV-View on Blazars
(Contributed talk)
W. Collmar
Max-Panck-Institut für Extraterrestrische Physik
The COMPTEL experiment aboard the Compton Gamma-Ray Observatory
pioneered the gamma-ray sky at MeV energies (0.75 to 30 MeV). It has
found evidence for 11 AGN: 10 blazars and the radio galaxy Centaurus
A. I will briefly review the main COMPTEL results by summarizing the
MeV properties (light curves, spectra, luminosities) of these COMPTEL
blazars, and - for interesting examples - put them in multifrequency
perspective.
Particular emphasis will be put on the Virgo blazars 3C 273 and 3C
279, which are among the best observed and most significant COMPTEL
sources. While 3C 273 is a rather stable MeV emitter with a smooth
spectral turnover at MeV energies on average, 3C 279 is a variable MeV
source in flux and spectrum. The COMPTEL results will be compared to
neighboring energy bands, in particular to the EGRET (>100 MeV) one.
Additionally, the main conclusions from 2 multifrequency campaigns on
these 2 sources in 1999 and 2000 will be presented. In summary, the MeV
results of 3C 273 and 3C 279 combined with neighboring energy bands
(in particular EGRET) indicate a multicomponent emission scenario for
their gamma-ray emission.
Optical and near infrared simultaneous observations of rapid
light variations in PKS 2155-304 and PKS 2005-489
(Poster)
T.P. Dominici, Z. Abraham & A. Galo
Instituto de Astronomia, Geofísica e Ciências
Atmosféricas - Universidade de São Paulo, Brazil
The existence of rapid light variations in some blazars is a well
confirmed phenomena, but until now is not clear what are the physical
mechanisms involved, mainly due the absence of simultaneous
multiwavelength observations, which could constrain the models. To shed
light in this discussion, we carried out simultaneous optical and near
infrared observations of the BL Lacs PKS 2005-489 and PKS 2155-304,
searching for microvariability in three campaigns of three days each
(July, August and November, 2001), with time resolution of about 10
minutes at optical wavelengths and better than 5 minutes at the
infrared. In the case of PKS 2005-489, microvariability in V and R
bands was observed in two nights, without counterparts in the B, I,
J and H bands. For PKS 2155-304, microvariability was detected at
optical bands in three nights and, in the infrared, we only observed
an achromatic variation of about 0.4 mag in time scales of months.
3C 66A: polarimetric monitoring in 1993 - 2001
(Poster)
Yu. S.Efimov
Crimean Astrophysical Observatory
Data of the UBVRI polarimetric monitoring of 3C 66A in 1993 -2001 are
presented and briefly discussed.
Discovery, identification and study of variability in blazars
(Contributed talk)
Fiorucci M., Marchili N., Ciprini S., Tosti G., Lubrano P.,
Cecchi C., Tramacere A.
I.N.F.N. Perugia; University of Perugia
We present statistical analysis of variability in a sample of blazars
observed at the Perugia Astronomical Observatory since 1992.
We briefly show how these statistical algorithms can be useful to
discriminate faint variable sources against the background noise.
This technique may used to discover and identify blazars with
high-energy detectors.
New 5-GHz VSOP Polarization Images of BL Lac Objects
(Contributed talk)
D. C. Gabuzda
University College Cork
An analysis of 5-GHz space-VLBI polarization images of several BL Lac
objects obtained using the HALCA orbiting antenna together with ground
VLB arrays is presented. Such results are now available for more than a
half dozen compact AGN. The general tendencies shown by these
high-resolution, relatively low-frequency images are discussed.
Characteristic Evolution of the VLBI Total Intensity and
Polarization Structure of BL Lac Objects
(Poster)
N. N. Garnich, D. C. Gabuzda, and T. V. Cawthorne
Sternberg Astronomical Institute, Moscow State University
We are engaged in an ongoing multi-frequency, multi-epoch
study of the VLBI properties of a complete sample of 1-Jy
BL Lac objects. Multi-epoch VLBI polarization observations
at 6 cm have now been analyzed for the entire sample.
We present an analysis of the characteristic evolution of
the total intensity and polarization structures of these
radio-loud BL Lac objects. The superluminal motions displayed
by the sample objects are systematically lower than for
a similar sample of core-dominated quasars.
The inner jet: Intensive mm-VLBI monitorings vs. RHD+emission
simulations
(Contributed talk)
Jose-Luis Gomez et al.
Instituto de Astrofisica de Andalucia (CSIC)
The inner jet structure is analyzed by comparision between
intensive mm-VLBI monitorings and relativistic hydrodynamic
and emission simulations of jets.
A continued monitoring of the radio galaxy 3C120 covering
more than 3 years of monthly polarimetric mm-VLBI reveal a
jet region where superluminal components flash on
and off over time scales of months. This is interpreted as
the interaction of the jet with a cloud of properties
intermediate between those of the broad and narrow
emission-line regions. Furthermore, several radio knots are
observed to appear in the weak of a new superluminal
component, moving at proper motions about 4 times slower
than any of the other moving knots observed in 3C120.
These features have properties similar to those of the
"trailing" shocks seen in relativistic time-dependent
hydrodynamical and emission simulations of compact jets.
This agreement between observations and simulations
reinforces the idea that the non-linear fluid character of
jets in AGNs and microquasars is determining most the
observational features seen in these objects.
Statistical correlations between optical and radio regimes in AGN
(Poster)
M.T. Hanski, L.O.Takalo & E.Valtaoja
Tuorla Observatory
We present a new method for correlating optical and radio variations
in AGN. The radio light curves are replaced by a model radio light
curve that consists of a set of exponential flares and a quiescent flux
component. At each epoch of time, three values, representing the radio
stage of the source at that time, can be determined: the phase and
flux level of the flare and the flux level of the model light curve.
These values are calculated for the concurrent radio model flare at
each epoch of optical observation. This method gives a statistical
comparison between optical and radio flux levels.
VLT multi-object spectroscopy of EGRET-detected BL Lac objects
(Contributed talk)
Jochen Heidt
Landessternwarte Heidelberg
VLT multi-object spectroscopy of the two EGRET detected
BL Lac objects OJ 287 and PKS 0537-441 will be presented.
Both BL Lacs are unique among their class. Whereas OJ 287 may
harbour a binary black hole in its center, PKS 0537 is one
of the intrinsically brightest of all BL Lac objects known.
The aim of the observations is to search for further
evidence for a binary black hole in OJ 287, e.g. by
identifying nearby companion galaxies. These may be relics
of a former galaxy group, whose evolution finally have led to
the formation of a binary black hole. Contrary, PKS 0537-441
has been discussed as a BL Lac, whose properties are
affected by gravitational microlensing effects. The
spectroscopical observations are able to clarify this issue.
An attempt to measure the redshift of the host
galaxies of these BL Lacs will also be presented.
Multi-wavelength observations of the TeV Blazars Mkn 421 with
the HEGRA Cherenkov telescopes and X-ray satellites
(Contributed talk)
Dieter Horns for the HEGRA collaboration
Max-Planck-Institut für Kernphysik, Heidelberg, Germany
Recent results obtained with the HEGRA system of imaging
Cherenkov telescopes on the TeV emission of the Blazars Mkn
421 and H1426+428 are reported. The energy spectra and light
curve for Mkn 421 during the strong activity in the
observational periods 1999/2000 and 2000/2001 are discussed
in the framework of Blazar models. Simultaneously
taken data with the RXTE X-ray satellite allow for
initial modeling of the strong flares with
indications for spectral variability in the TeV-band.
The high energy peaked
Blazar H1426+428 has recently been identified as a source of
TeV photons. Due to its red shift of z=0.129, absorption of
TeV photons due to pair-production on the optical and near
infrared extragalactic light becomes important and should
leave a signature in the observed TeV energy spectrum.
Noticeably, the TeV energy spectrum determined with the
HEGRA system of Cherenkov telescopes agrees with the
expectation of a heavily absorbed source spectrum. The
difficulties of modeling the broad-band spectral energy distribution
with conventional Blazar models (SSC,EC) are discussed.
The Long Term Analyses of Blazars in Ondrejov
(Contributed talk)
Rene Hudec, INTEGRAL ISDC and OMC teams
Astronomical Institute Ondrejov
We will discuss the long-term blazar monitoring projects with the
involvement of the High Energy Astrophysics Group at the Ondrejov
Observatory. We will describe and discuss the results
provided by the small robotic BART telescope. We will also
report on the recent collaborative efforts to digitize
astronomical archival plates to be able to use powerful
computers to analyse the data included in the plates. The
analyses of CVs and related objects represent also an
important part of scientific program of the new ESA
INTEGRAL satellite expected to be launched in October 2002.
We will review the capabilities of the onboard
instrumentation as well as scheduled observations to
investigate blazars, with the focus on the optical OMC
camera. We will show and discuss a list of blazars and
AGNs located in the INTEGRAL galactic scans as well as
inside approved pointed observations.
Lobster Eye: New X-Ray Telescope to Monitor the Sky
(Poster)
R. Hudec, A. Inneman, L. Pina
Astronomical Institute Ondrejov
We will report on fully innovative very wide-field of view X-ray
telescopes of the Lobster Eye geometry. The first prototypes confirm
that these devices may play an important role in very sensitive sky
monitoring in X-rays and hence in understanding the physical processes
and evolution of highly variable X-ray sources including AGNs and
blazars.
Long -Term Monitoring of Blazars by the BART Robotic Telescope
()
R. Hudec, M. Jelinek, M. nekola, BART Team
Astronomical Institute Ondrejov
We report on the project of small optical robotic telescope BART
dedicated to high energy astronomy. The primary scientific goal of
BART is to provide immediate optical observations of high energy
triggers such as GRBs provided by satellites. I the meantime, the
BART telescope monitors regularly the selected sources i.e. provides
long-term monitoring over extended time intervals. The selected blazars
and AGNs located inside the ESA INTEGRAL satellite galactic scans and
approved pointed observations are already investigated this way.
The results of the test operation will be presented and discussed, as
well as the role of small optical robotic telescopes in recent and
future blazar projects and analyses in general. It will be shown that
such devices can monitor selected sources for sudden activity states
resulting in ToO (target of opportunity) satellite observations as well
as to provide valuable simultaneous data for multispectral analyses.
Efforts to develop such dedicated telescopes with larger apertures
will be also addressed.
Long-Term Monitoring of Blazars with Archival Sky Patrol
(Poster)
R. Hudec, F. Krolupper
Astronomical Institute Ondrejov
We report on the recent efforts to digitize the sky plate archives
and to use these data for various scientific projects including
analyses of blazars and related objects. We will also address and
discuss the status of the development of related algorithms and
software programs. These data may easily provide very long term
monitoring over very extended time intervals (up to more
than 100 years) with limiting magnitudes between 12 and 23.
Superluminal motion of Gamma-Ray Blazars
(Contributed talk)
S.G. Jorstad, A.P. Marscher, M.L. Lister, A. Stirling
Institute for Astrophysical Research, Boston University
The results of a program to monitor the structure of the
radio emission in 42 gamma-ray blazars reveal that the
apparent superluminal motions in gamma-ray sources are much
faster than for the general population of bright compact
radio sources (proper motions are determined in 33 sources).
We have performed a 3-year program of bimonthly polarimetric
observations of 15 quasars, BL Lac objects, and radio
galaxies with the VLBA at 43 GHz. 10 of these 15 sources are
gamma-ray blazars. We compare the results for the
superluminal motions obtained during the programs and analyse
some interesting cases of an interaction between moving and
stationary jet features.
VLBA Observations of Superluminal Motion in Blazars
()
K. I. Kellermann
National Radio Astronomy Observatory
Since 1995 we have been using the VLBA at 15 GHz to study the
relativistic outflow in a sample of 174 AGN jets. Our observations
include quasars, AGN, and BL Lac objects, GPS sources and CSOs as well
as the more luminous one-sided core-jet blazers. We discuss the
statistics of the observed motions with the aim of understanding the
relation among the AGN classes.
Typically we have from three and seven observations of each source made
at intervals between 6 and 18 months, and we are able to determine
motions with an accuracy of about 0.1 mas/year. The observed velocities
range from subluminal to more than 20c. For those sources with well
defined moving features, we have also examined their 2 dimensional track
with the aim of distinguishing between ballistic motion and curved
trajectories. We discuss the amount of Doppler boosting based on our
observed Lorentz factors and compare this with observations of
variability and apparent brightness temperature
TeV observations of BL Lacs objects with the CAT Cherenkov
telescope
(Contributed talk)
Khelifi Bruno for the CAT collaboration
PCC - Collège de France, Paris, France
Since 1998, the CAT Imaging Atmospheric Cherenkov telescope has
observed the BL Lac object IES 1428+428. We will present the flux and
the measured spectra from these observations.
The analysis of results from other TeV blazars candidates will also be
presented.
Black hole masses of BL Lac objects
(Contributed talk)
J.K. Kotilainen, R. Falomo, A. Treves
Tuorla Observatory, Finland; Osservatorio Astronomico di
Padova, Italy; Universita dell'Insubria, Italy
The correlation between black hole mass M(BH) and stellar
velocity dispersion sigma in nearby elliptical galaxies
affords a novel way to determine M(BH) in active galaxies.
We report on measurements of sigma from optical spectra of a
sample of BL Lac host galaxies. The derived values of sigma
are in the range of 150 - 300 km/s corresponding to M(BH) of
5 x 10^7 to 10^9 Msun. The average ratio of M(BH) to the host
galaxy mass is 0.0014, consistent with that estimated in
other active and inactive galaxies. The velocity dispersions
and the derived values of M(BH) of the BL Lacs are similar to
those obtained for low redshift radio galaxies, in good
agreement with the predictions of the unified models for
radio-loud active galaxies.
Compact Structures in the Central Engines of Active Galactic
Nuclei
(Contributed talk)
Y.Y. Kovalev
Astro Space Center of P.N.Lebedev Physical Institut
We have used visibility data obtained with VLBA at 15 GHz to
examine the most compact structure in 170 flat spectrum extragalactic
radio sources. With projected baselines out to 440 million
wavelengths we are able to discuss source structure on angular
scales as small as 0.2 mas. This is comparable with space VLBI data
from VSOP obtained on longer baselines but at longer wavelengths and
with lower accuracy. For about 40\% of the sources, more than half
of the flux density is unresolved on the longest baselines and have
dimensions less than 0.2 mas, at least at one epoch. The most
variable sources tend to have the most compact structure. Typical
lower limits to the brightness temperature are in the range of,
$10^{11}$ to $10^{12}$~K, but extends up to $3\cdot10^{12}$~K in
apparent excess of the inverse Compton limit of stationary
synchrotron sources. Longer baselines, such as will be possible from
future space VLBI missions will be needed to study the most compact
high brightness temperature regions in these sources. The fringe
visibility of the gamma-ray sources is more variable than for non
gamma-ray sources. This supports models with a common emission
mechanism at radio and gamma-ray wavelengths.
TeV observation of BL Lac objects
(Invited talk)
Daniel Kranich for the HEGRA collaboration
MPI für Physik München
During the ~7 years of existence of the HEGRA Cherenkov telescopes a
large fraction of the time was spent on the observation of BL Lac
objects. Here we present an overview of the main results and give an
outlook on the next generation Cherenkov telescopes.
Millimeter Variability of AGN Jets
(Contributed talk)
T.P. Krichbaum
Max-Planck-Institut für Radioastronomie
We show new data on which we discuss the correlation between flux
density flares observed in mm-radio bands and the observed
structural variations on the sub-parsec scale regions
in the jets of those AGN, which we imaged with VLBI
at cm- and mm-wavelengths with angular resolutions of up
to 50 micro-arcseconds.
Inverse Compton modeling of AGNs
(Contributed talk)
A. Lähteenmäki & E. Valtaoja
Metsähovi Radio Observatory, Finland;Tuorla Observatory,
Finland
We have studied the connection between radio and gamma-ray
emission in AGNs to find out by which mechanism the gamma-ray
emission is produced in these sources. We also examine
the synchrotron peak frequency of a sample of AGNs and how
its location implies a sequence in source properties.
Connection between X-ray and Radio-Optical Emission in Blazars
(Invited talk)
Alan P. Marscher
Boston University
We have been monitoring the X-ray emission from several blazars and
the radio galaxy 3C 120 with RXTE since 1996. The high density of the
monitoring (1-7 times per week) has allowed us to accumulate detailed
long-term X-ray light curves that can be compared with similar radio
and optical light curves and with times of ejection of superluminal
radio knots. We find strong evidence that events in the accretion
disk of 3C 120 cause superluminal ejections. For two years, radio
flares preceded X-ray flares in PKS 1510-089 by about 2 weeks, which
indicates that the light curves are affected by light-travel delays.
Optical variations in 3C 279 usually correlate very well with X-ray.
In both of these quasars, superluminal ejections usually occur
during an X-ray outburst. It appears that the X-ray and optical
emission in blazars comes mainly from the core of the radio jet,
not close to the black hole.
Magnetically confined base in the jet of R Aqr
(Poster)
Mäkinen, K.K. (1), Johnson, D.R.H. (2) & Lehto, H.J. (1)
(1) Tuorla Observatory, Finland
(2) Charterhouse, Surrey, UK
We have detected polarization at the base of the radio jet in
R Aqr symbiotic star system. The observations were made with the VLA.
The polarization pattern is reminiscent of the radio jet model for
AGNs.
The Whole Earth Blazar Telescope and the BL Lac Campaigns
2000-2001
(Poster)
Villata M. et al.
INAF, Osservatorio Astronomico di Torino, Pino Torinese,
Italy
The Whole Earth Blazar Telescope (WEBT) is an international
consortium of optical observatories devoted to blazar monitoring
during optical and multiwavelength campaigns.
The preliminary results of the BL Lac Campaigns 2000 and 2001 shown
here represent one of the most successful examples of the WEBT
potential.
Spectral Behaviour and Variability of Blazars: The Helical-Jet
Interpretation
(Contributed talk)
Ostorero L. (1), Villata M. (2), Raiteri C.M. (2)
(1)Universita di Torino, Dipartimento di Fisica Generale;
(2) Osservatorio Astronomico di Torino
Multi-epoch simultaneous spectral energy distributions (SEDs)
of some BL Lac objects and their interpretation in term of
the helical-jet model by Villata & Raiteri (1999) are presented.
The model is also applied to explain both the quasi-periodic
behaviour of radio and optical light curves and the
long-term variability of the SED of AO 0235+16.
Synchrotron X-ray Emission from Flat-spectrum Radio Quasars
(Contributed talk)
P. Padovani, L. Costamante, G. Ghisellini, P. Giommi, E.
Perlman
STScI/ESA, Univ. di Milano, Brera Obs., ASDC, UMBC
We present new BeppoSAX observations of four flat-spectrum radio
quasars (FSRQ) having effective spectral indices alpha_ro and alpha_ox
typical of high-energy peaked BL Lacs. The BeppoSAX band in one of our
sources is dominated by synchrotron emission peaking at ~ 2 10^16 Hz,
as also shown by its steep (alpha_x ~ 1.5) spectrum, making this
the first known FSRQ whose X-ray emission is not due to inverse
Compton radiation. Two other sources display a flat spectrum
(alpha_x ~ 0.7) but with indications of steepening at low X-ray energies.
This is also supported by ROSAT and multifrequency data and a
synchrotron inverse Compton model, which suggests synchrotron peak
frequencies ~ 10^15 Hz, typical of intermediate BL Lacs. Our sources have
powers more typical of high-energy peaked BL Lacs than of FSRQ, close to
the low-luminosity end of the FSRQ luminosity function. We discuss this
in terms of an anti-correlation between synchrotron peak frequency and
total power, based on physical arguments, and also as due to a selection
effect.
Spectroscopic measurements of 15 RGB BL Lac objects
(Poster)
M. Pasanen, K. Nilsson, J. Heidt, L. Takalo
Tuorla observatory, Finland
The RASS-Green Bank (RGB) BL Lac sample consists of 127 objects. Out
of these, redshifts are known for approximately one-half. We have
spectroscopic observations for 15 objects obtained at the Calar Alto
2.2 m telescope. All of them have optical magnitudes around 18 mag. We
attempted to determine their redshifts, but were successful for one
object only (RGB2039+523, z=0.053) with any confidence. The rest
showed no promising identifiable absorption or emission lines.
High energy monitoring of Blazars
(Invited talk)
E. Pian
Osservatorio Astronomico di Trieste
Blazars exhibit flux and spectral variations of largest
amplitude at the highest frequencies. Therefore,
monitoring their variability at X- and gamma-rays
is the most effective tool to peer into the mighty
powerhouse of these sources. High energy observations
of the brightest BL Lac sources (e.g., PKS 2155-304,
Mkn501, Mkn421) with the latest generation of satellites
and Cerenkov telescopes have allowed a detailed study
of their behavior and have critically improved our
understanding of the physics of blazar jets. I will
review some of the recent results of blazar
multiwavelength monitoring with emphasis on the X-ray
campaigns and I will outline some of the future programs
for blazar investigation from space, particularly with
INTEGRAL.
Quasi-periodic Activity in the Blazar 0059+581
(Poster)
Pyatunina, T.B., Gabuzda, D.C., Terasranta, H., Aller, H.D.,
Aller, M.F.
IAA of the RAS, St-Petersburg, Russia; University College,
Cork, Ireland; Metsahovi Radio Research Station, Finland;
University of Michigan, USA
Inspection of compiled radio light curves at frequencies from 4.8 to
37 GHz constructed using data from the Metsahovi Radio Research Station
and the UMRAO, as well as the 8-GHz VLBI images, for period (1994-2001)
suggests the presence of quasi-periodic flares in the radio flux
density that occur approximately every two years. There is evidence
that alternating flares are optically thick (associated with the core)
and optically thin (associated with the evolution of the jet). This in
turn suggests that the duration of the entire cycle of the
quasi-periodic activity is ~4 years, with two peaks per cycle. One
possible scenario is that the first peak is associated with the
ejection of a new VLBI component, while the second is associated
with a flare in the ejected component as it propagates from the core.
Rapid Evolution of the Parsec-Scale Structure of the BL Lac
Object 1219+285
(Poster)
D. C. Gabuzda and E. A. Rastorgueva
Sternberg Astronomical Institute
We are studying the evolution of the parsec-scale structure of
1219+285 using a dense series of VLBI total intensity and
polarization images at 1 and 2~cm obtained at nine epochs
spanning three years. There is very rapid evolution of the
VLBI structure in some periods, with the appearance of the
images changing drastically between epochs separated by only
a few months. A number of superluminal components can be
identified, and their motions will be analyzed to study the
systematics of their motion from the core (e.g. evidence for
acceleration or deceleration with distance from the core).
1219+285 is one of only a few active galactic nuclei for
which there is good evidence for periodicity in the optical
variability (Belokon et al. 2000). Further, our series of
VLBI images will be used to search for possible correlations
between various changes in properties of the VLBI structure
and the optical variations.
The Radio Structure of High-Energy Peaked BL Lacertae Objects
(Poster)
Travis Rector
National Radio Astronomy Observatory
We present VLA and first-epoch VLBA observations that are part of a
program to study the parsec-scale radio structure of a sample of
fifteen high-energy-peaked BL Lacs (HBLs). The sample was chosen to
span the range of logarithmic X-ray to radio flux ratios observed in
HBLs. As these are only the first epoch of observations, proper
motions of jet components are not yet available; thus we consider
only the structure and alignment of the parsec- and kiloparsec-scale
jets. Whereas low-energy-peaked BL Lacs (LBLs) show a wide
distribution of parsec- and kpc-scale jet alignment angles, most of
the HBLs studied here have well-aligned jets, suggesting that HBL
jets are either intrinsically straighter or are seen further
off-axis than LBL jets.
The periodical variability and the central black hole system in
Mkn501
(Contributed talk)
F.M. Rieger, K. Mannheim
University of Würzburg and University Observatory
Göttingen
We investigate the increasing evidence for a 23 day
periodicity during the 1997 high state of Mkn501 with
respect to their implications for the central mass system.
To this aim, two scenarios for the geometrical origin of
periodicity are analysed, i.e. the binary black hole and
the lighthouse model. This allows a discrimination due to
the size of the expected central BH mass. Independent BH
mass estimates from high energy emission models and host
galaxy observations are evaluated and their significance
for the models presented is discussed.
Connections between millimeter continuum flares
and the parsec-scale jet structure in blazars
(Contributed talk)
T. Savolainen, K. Wiik & E. Valtaoja
Tuorla observatory, Finland
We have compared the total flux density
variations in 27 gamma-ray blazars with
the structural changes in their parsec-scale
jets using multi-epoch VLBA observations at
22 and 43 GHz together with data from
Metsähovi quasar monitoring program at 22
and 37 GHz. There is a clear connection
between total flux density outbursts and VLBI
components emerging into the jet. Ejections
of the VLBI components are coincident with
the beginning times of the total flux density
flares, and they also show similar flux
evolution. Our results suggest that all radio
variations are related to shocks propagating
in the jet.
In our sources, it looks like a large fraction
of the shocks grow and decay within the innermost
few tenths of a milliarcsecond and therefore we
see them only as so-called 'core flares' in the
VLBI maps. However, with present data we cannot
exclude the possibility that the core itself also
brightens (and thus contributes to the flare) as
a shock passes through it.
High-resolution imaging of EGRET blazars
(Poster)
T. Schafeitel, K. Nilsson, J. Heidt, A. Sillanpää,
L.O. Takalo
Tuorla Observatory, Finland
We present results of a high-resolution imaging study of 19 blazars in
the redshift range z = 0.3 up to 2.2, detected by EGRET. The host
galaxies were studied by fitting two-dimensional galaxy + core models
to the observed surface brightness distribution. We were able to model
the host galaxy for two of the observed blazars. The core model was
fitted to the rest of the blazars. Absolute magnitudes of the hosts
and cores were calculated from the models.
Temperature-dependent radiation transport in AGN jets
(Poster)
Mark Siewert
Ruhr-Universität Bochum
Photon production in the channeled blast wave model of
particle accelertion in AGN is investigated under the
aspect of the plasma temperature. The temporal evolution
of the temperature in the accelerated plasma is analyzed.
The optical thickness is presented as a function of
temperature and the resulting synchrotron emission of
photons is compared with temperature-independent
calculations. Preliminary results are presented.
Precision Photometry of Radio Intermediate Quasars
(Contributed talk)
Niall Smith, Aidan O'Connor, Stephen O'Driscoll, John Howard
Cork Institute of Technology
It has been suggested that Radio Intermediate Quasars (RIQ)
represent objects which emit jets with low bulk kinetic
energies. In this talk we present the results of a programme
of intensive two-colour optical monitoring of a sample of
RIQs designed to characterise the short-timescale variability
in these objects. The data indicates no evidence for rapid
fluctuations (on timescales of tens of
minutes), but does provide evidence for inter-night
variability at the few mmag level. We discuss the
observational methodologies and data reduction techniques
that we employ to reach differential photometric precisions
as high as +/-0.1%. We also briefly discuss future prospects
for rapid variability studies in these objects and in
blazars.
A Theoretical Study of Multifrequency Variability in Blazar
Jets
(Poster)
Andrei Sokolov
Boston University
I have developed a model of production and transfer of time-dependent
radiation in relativistic jets. Using this model, I have simulated
multifrequency variability of the synchrotron and inverse Compton
emission. Calculation of the latter uses integration over the
population of relativistic electrons and the spectrum of the incident
emission, which can be delayed due to the light travel time effects.
The inclusion of light travel time effects for the synchrotron
self-Compton (SSC) calculation and careful treatment of the
evolving population of relativistic electrons in the model yields a
good fit to the March 1999 flare of 3C 273 (McHardy et al, in
preparation), which had an unusual reverse time delay (infrared
emission leads x-rays). The model fit determines the number density
of relativistic electrons and the magnetic field strength in the source.
The radio events during the strongest gamma outbursts in
Blazars
(Poster)
Harri Teräsranta, Seppo Wiren, Pertti Koivisto
Metsähovi radio observatory
The radio behaviour at millimeter wavebands during the
strongest gamma-ray events found in Blazars by EGRET are
investigated.
Radio spectra and variability of EGRET blazars
(Contributed talk)
Tornikoski, M., Lähteenmäki, A., Lainela, M., Valtaoja, E.,
Jussila, I. & Parviainen, M.
Metsähovi Radio Observatory, Finland; Tuorla Observatory,
Finland
We present radio spectra and cm- to mm-variability of
a set of AGNs that are probable or possible counterparts
of the EGRET detections in the Third ERGET Catalog.
We discuss the typical radio-to-mm properties of the
gamma-bright blazars.
The Whole Year Blazar Telescope (WYBT)
(Poster)
G.Tosti(1), M.Villata(2), M. Carini(3) for the WYBT Collaboration
1) Department of physics University of Perugia
2)INAF-Torino Astronomical Observatory
3)Department of Physics and Astronomy, Western Kentucky University
The Whole Year Blazar Telescope (WYBT) is a recently formed
consortium of optical observers dedicated to carrying out a
long-term monitoring program of a sample of blazars.
One of the main WYBT goals will be that of providing the optical
support needed to maximize the scientific return from the
high-energy observations of the next space missions such as AGILE.
Here we present the scientific motivations for this enterprise and some
preliminary results.
Comparing the properties of synchrotron outbursts in quasars
and microquasars
(Contributed talk)
Marc Türler
INTEGRAL Science Data Centre & Geneva Observatory
Microquasars are black hole binary systems in our galaxy,
which have similar properties than the much more powerful
distant quasars. In particular, they have a relativistic
jet in which structures were observed to move with apparent
superluminal speed. In GRS 1915+105, blobs of material seem
to be ejected simultaneously in the jet and the counter-jet,
whereas in a quasar like 3C 273, the counter-jet is not
observed and the structures in the jet are likely to be
propagating shock waves. There is good evidence that these
structures seen in the jet are related to the onset of
synchrotron outbursts producing strong millimeter and radio
flux enhancements. The aim of this contribution is to
compare quantitatively the properties of synchrotron
outbursts in the microquasar GRS 1915+105 with the properties
found in the quasar 3C 273.
Conversion of blast-wave energy into radiation: particle
transport effects
(Contributed talk)
R. Vainio
Space Research Laboratory, VISPA
Dense, collimated ultrarelativistic blast waves picking up ambient
particles have been considered as sources of electromagnetic radiation
extending from radio to gamma-ray frequencies in AGN. The present study
extends the previous momentum-space modeling to include particle transport
in one spatial dimension. Different models of particle tranport are
considered inside the dense blast wave, and in all cases, particle
transport effects are shown to have a profound influence on the emission
characteristics of the blast waves.
Blazars: the view from AGILE
(Invited talk)
Stefano Vercellone on behalf of the AGILE Team
IASF-CNR Sezione di Milano "G. Occhialini"
I will review the current status of the AGILE Mission, its
performance and timeline.
For the first time, simultaneous monitoring of a large
number of AGNs per pointing will be possible in the 30MeV -
50 GeV and 10 - 40 keV energy bands, thanks to an excellent
angular resolution and an unprecedently large field of view
(~ 1/5 of the entire sky above 30 MeV).
I will also show some recent results on the possible AGILE
contribution to the study of Blazars in the gamma-ray and
hard X-ray energy bands.
Simulations on the effect of internal structure of shock fronts
on particle acceleration
(Poster)
J. Virtanen, R. Vainio
Tuorla Observatory and Space Research Laboratory, VISPA,
Finland
We have studied how the internal structure of shock fronts in
relativistic jets affects the energy spectrum of accelerated
particles. Monte Carlo simulations are employed to determine the
spectral indices of the power-law spectra of accelerated electrons in
shocks of various finite widths and different types of electromagnetic
turbulence.
Direct imaging studies of X-ray jets
(Invited Talk)
Stefan Wagner
Landesternwarte Heidelberg-Königstuhl
I will review direct imaging studies of blazar jets at X-ray energies.
More than a dozen jets have been studied in recent experiments. The
X-ray emission mechanisms and implications for Blazar jet models will
be discussed.
Curvature of the CTA 102 jet
(Poster)
Rantakyrö, Wiik, Tornikoski, Valtaoja, Bååth
The structure of the CTA 102 jet is investigated using multi-epoch
22, 43 and 86 GHz VLBI images.
The periodic IR and radio jets in Microquasar GRS~1915+105 and
the accretion disk jet connection
(Contributed talk)
J. S. Yadav
Tata Institute of Fundamental Research, Mumbai, India
The non-thermal emission in the microquasar GRS 1915+105 can be broadly
classified in three classes; 1. large relativistic superluminal radio
jets, 2. the periodic and quasi-periodic IR and radio baby jets and,
3. the persistent radio emission. The periodic baby jets occur during
the beta class of X-ray activity which is supposed to be the most
complex out of 12 separate X-ray classes observed in microquasar
GRS~1915+105. This X-ray class has been extensively studied in
multiwavelengths simultaneously. This class has all the three
basic states of the source and always accompanied by IR/radio
flares. We discuss the accretion disk-jet connection during this
class and compare the baby radio jets with large superluminal radio
jets.
The shape of the iron $K_alpha$ line as the evidence for the
BH's existence in Seyfert galaxies
(Contributed talk)
Zakharov, A.F., Repin S.V.
Institute of Theoretical and Experimental Physics
Observations of Seyfert galaxies in X-ray region reveal the
wide emissive lines in their spectra, which can arise in inner
parts of accretion disks, where the effects of General Relativity (GR)
must be counted. A spectrum of a solitary emission
line (the $K_\alpha$-line of iron, for example)
of a hot spot in Kerr accretion disk is simulated, depending
on the radial coordinate $r$ and the angular momentum $a=J/M$ of a
black hole, under the assumption of an equatorial circular motion of
a hot spot. Basing on results of numerical simulations
it is shown that the characteristic two-peak line profile
with the sharp edges arises at a large distance,
(about $r \approx (3-10)r_g$). The inner regions emit the line, which
is observed with one maximum and extremely wide red wing. High
accuracy future spectral observations, being carried out, could
detect the angular momentum $a$ of the black hole.
Last updated: 05 June 2002 by
Rami T. F. Rekola