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. Chernin^1,2
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. L�hteenm�ki & 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 Mets�hovi 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)
Rantakyr�, 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