Blazar Times - No. 62 - April 2004
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| The Blazar Times |
| A Research Newsletter Dedicated to the BL Lac and Blazar Phenomena
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| No. 62 - April 2004 | Editor: Travis A. Rector (blazar@uaa.alaska.edu)
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TABLE OF CONTENTS
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
For preprints contact: villata@to.astro.it
For preprints via ftp or WWW:
http://www.to.astro.it/blazars/bllac2001a_preprint.zip
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
For preprints contact: kkellerm@nrao.edu
For preprints via ftp or WWW:
http://xxx.lanl.gov/abs/astro-ph/0403320
Abstract Guidelines
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