Blazar Times - No. 62 - April 2004
The Blazar Times
A Research Newsletter Dedicated to the BL Lac and Blazar Phenomena
No. 62 - April 2004 Editor: Travis A. Rector (


Journal Abstracts 1
Abstract Guidelines 4

Journal Abstracts
The WEBT BL Lacertae Campaign 2001 and its extension. Optical light curves and colour analysis 1994-2002
M. Villata1, C. M. Raiteri1, O. M. Kurtanidze2,3,4, M. G. Nikolashvili2, M. A. Ibrahimov5, I. E. Papadakis6,7, G. Tosti8, F. Hroch9, L. O. Takalo10, A. Sillanpää10, V. A. Hagen-Thorn11,12, V. M. Larionov11,12, R. D. Schwartz13, J. Basler13, L. F. Brown14, T. J. Balonek15, E. Benítez16, A. Ramírez16, A. C. Sadun17, P. Boltwood18, M. T. Carini19, D. Barnaby19, J. M. Coloma20, J. A. Ros20, B. Z. Dai21,22,23, G. Z. Xie21,22,23, J. R. Mattox24, D. Rodriguez25, I. M. Asfandiyarov5, A. Atkerson19, J. L. Beem14, S. D. Bloom26, S. M. Chanturiya2, S. Ciprini8, S. Crapanzano1, J. A. de Diego16, N. V. Efimova11, D. Gardiol1,27, J. C. Guerra27, B. B. Kahharov5, B. Z. Kapanadze2, H. Karttunen10, T. Kato28, G. N. Kimeridze2, N. A. Kudryavtseva11, M. Lainela10, L. Lanteri1, E. G. Larionova11, M. Maesano29, N. Marchili8, G. Massone1, T. Monroe19, F. Montagni30, R. Nesci31, K. Nilsson10, J. C. Noble32, G. Nucciarelli8, L. Ostorero4,33, J. Papamastorakis7,6, M. Pasanen10, C. S. Peters14, T. Pursimo34, P. Reig35,6, W. Ryle19, S. Sclavi31, L. A. Sigua2, M. Uemura28  and W. Wills19
1 Istituto Nazionale di Astrofisica (INAF), Osservatorio Astronomico di Torino, Via Osservatorio 20, 10025 Pino Torinese (TO), Italy
2 Abastumani Astrophysical Observatory, 383762 Abastumani, Georgia
3 Astrophysikalisches Institut Potsdam, An der Sternwarte 16, 14482 Potsdam, Germany
4 Landessternwarte Heidelberg-Königstuhl, Königstuhl 12, 69117 Heidelberg, Germany
5 Ulugh Beg Astronomical Institute, Academy of Sciences of Uzbekistan, 33 Astronomical Str., Tashkent 700052, Uzbekistan
6 IESL, FORTH, 711 10 Heraklion, Crete, Greece
7 Physics Department, University of Crete, PO Box 2208, 710 03 Heraklion, Crete, Greece
8 Dipartimento di Fisica, Università di Perugia, Via A. Pascoli, 06123 Perugia, Italy
9 Institute of Theoretical Physics and Astrophysics, Faculty of Science, Masaryk University, Kotlárská 2, 611 37 Brno, Czech Republic
10 Tuorla Observatory, 21500 Piikkiö, Finland
11 Astronomical Institute, St.-Petersburg State University, Universitetsky Pr. 28, Petrodvoretz, 198504 St.-Petersburg, Russia
12 Isaac Newton Institute of Chile, St.-Petersburg Branch
13 Department of Physics and Astronomy, University of Missouri-St. Louis, 8001 Natural Bridge Road, St. Louis, MO 63121, USA
14 Department of Physics, Astronomy and Geophysics, Connecticut College, New London, CT 06320, USA
15 Foggy Bottom Observatory, Colgate University, 13 Oak Drive, Hamilton, NY 13346, USA
16 Instituto de Astronomía, UNAM, Apdo. Postal 70-264, 04510 México DF, Mexico
17 Department of Physics, University of Colorado at Denver, PO Box 173364, Denver, CO 80217-3364, USA
18 Boltwood Observatory, 1655 Main Street, Stittsville, Ontario K2S 1N6, Canada
19 Department of Physics and Astronomy, Western Kentucky University, 1 Big Red Way, Bowling Green, KY 42104, USA
20 Agrupació Astronòmica de Sabadell, PO Box 50, 08200 Sabadell, Spain
21 Yunnan Observatory, National Astronomical Observatories, Chinese Academy of Sciences, PO Box 110, Kunming 650011, China
22 United Laboratory of Optical Astronomy, Chinese Academy of Sciences, Beijing, China
23 Yunnan Astrophysics Center, Yunnan University, Kunming 650091, China
24 Department of Natural Sciences, Fayetteville State University, 1200 Murchison Road, Fayetteville, NC 28301, USA
25 Guadarrama Observatory, C/ San Pablo 5, Villalba 28409, Madrid, Spain
26 Department of Physics and Astronomy, Hampden-Sydney College, Hampden-Sydney, VA 23943, USA
27 Istituto Nazionale di Astrofisica (INAF), Telescopio Nazionale Galileo, Roque de los Muchachos Astronomical Observatory, PO Box 565, 38700 Santa Cruz de La Palma, TF, Spain
28 Department of Astronomy, Faculty of Science, Kyoto University, Kyoto, Japan
29 Stazione Astronomica Vallinfreda, Italy
30 Stazione Astronomica Greve in Chianti, Italy
31 Dipartimento di Fisica, Università La Sapienza, Piazzale A. Moro 2, 00185 Roma, Italy
32 Institute for Astrophysical Research, Boston University, 725 Commonwealth Ave., Boston, MA 02215, USA
33 Dipartimento di Fisica Generale, Università di Torino, Via P. Giuria 1, 10125 Torino, Italy
34 Nordic Optical Telescope, Roque de los Muchachos Astronomical Observatory, PO Box 474, 38700 Santa Cruz de La Palma, TF, Spain
35 G.A.C.E., Departament d'Astronomia i Astrofísica, Universitat de València, 46071 Paterna-València, Spain
BL Lacertae has been the target of four observing campaigns by the Whole Earth Blazar Telescope (WEBT) collaboration. In this paper we present UBVRI light curves obtained by the WEBT from 1994 to 2002, including the last, extended BL Lac 2001 campaign. A total of about 7500 optical observations performed by 31 telescopes from Japan to Mexico have been collected, to be added to the ~ 15600 observations of the BL Lac Campaign 2000. All these data allow one to follow the source optical emission behaviour with unprecedented detail. The analysis of the colour indices reveals that the flux variability can be interpreted in terms of two components: longer-term variations occurring on a few-day time scale appear as mildly-chromatic events, while a strong bluer-when-brighter chromatism characterizes very fast (intraday) flares. By decoupling the two components, we quantify the degree of chromatism inferring that longer-term flux changes imply moving along a ~ 0.1 bluer-when-brighter slope in the B-R versus R plane; a steeper slope of ~ 0.4 would distinguish the shorter-term variations. This means that, when considering the long-term trend, the B-band flux level is related to the R-band one according to a power law of index ~ 1.1. Doppler factor variations on a "convex" spectrum could be the mechanism accounting for both the long-term variations and their slight chromatism.
Accepted by A&A
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Sub-milliarcsecond Imaging of Quasars and Active Galactic Nuclei
III. Kinematics of Parsec-Scale Radio Jets
K. I. Kellermann1, M. L. Lister1,2, D. C. Homan1,3, R. C. Vermeulen4, M. H. Cohen5, E. Ros6, M. Kadler6, J. A. Zensus6,1, Y. Y. Kovalev7,8
1 National Radio Astronomy Observatory, 520 Edgemont Road, Charlottesville, VA 22903-2475, U.S.A.
2 Department of Physics, Purdue University, 525 Northwestern Avenue, West Lafayette, IN 47907, U.S.A.
3 Department of Physics and Astronomy, Denison University, Granville, OH 43023, U.S.A.
4 ASTRON, Postbus 2, NL-7990 AA Dwingeloo, Netherlands
5 Department of Astronomy, Mail Stop 105-24, California Institute of Technology, Pasadena, CA 91125, U.S.A.
6 Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, D-53121 Bonn, Germany
7 National Radio Astronomy Observatory, P.O. Box 2, Green Bank, WV 24944, U.S.A.
8 Astro Space Center of P.N. Lebedev Physical Institute, Profsoyuznaya 84/32, 117997 Moscow, Russia
We report the results of a 15 GHz (2 cm) multi-epoch VLBA program, begun in 1994 to study the outflow in radio jets ejected from quasars and active galaxies. The observed flow of 208 distinct features measured in 110 quasars, active galaxies, and BL Lac objects shows highly collimated relativistic motion with apparent transverse velocities typically between zero and about 15c, with a tail extending up to about 34c. Within individual jets, different features appear to move with a similar characteristic velocity which may represent an underlying continuous jet flow, but we also see some stationary and even apparently inward moving features which co-exist with the main features. Comparison of our observations with published data at other wavelengths suggests that there is a systematic decrease in apparent velocity with increasing wavelength, probably because the observations at different wavelengths sample different parts of the jet structure.
The observed distribution of linear velocities is not consistent with any simple ballistic model. Either there is a rather broad range of Lorentz factors, a significant difference between the velocity of the bulk relativistic flow and the pattern speed of underlying shocks, or a combination of these options. Assuming a ballistic flow, comparison of observed apparent velocities and Doppler factors computed from the time scale of flux density variations is consistent with a steep power law distribution of intrinsic Lorentz factors, an isotropic distribution of orientations of the parent population, and intrinsic brightness temperatures about an order of magnitude below the canonical inverse Compton limit. It appears that the parent population of radio jets is not dominated by highly relativistic flows, and contrary to the assumption of simple unified models, not all sources have intrinsic speeds close to c.
Usually, the observed jet flow is in the general direction of an established jet. However, many jets show significant bends and twists, where the observed motions are non-radial, but are alingned with the local jet direction suggesting that the jet flow occurs along pre-existing bent channels. In a few cases we have observed a clear change in the direction of a feature as it flows along the jet. Radio jets which are also strong gamma-ray sources detected by EGRET appear to have significantly faster speeds than the non EGRET sources, consistent with the idea that gamma ray sources have larger Doppler factors than non gamma-ray sources. Sources at high redshift have systematically lower angular speeds than low redshift jets, consistent with standard cosmologies.
Accepted by ApJ
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On 13 Apr 2004, 11:31.