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          Institute: MPI für Kernphysik     Collection: High-Energy Astrophysics     Display Documents

ID: 51240.0, MPI für Kernphysik / High-Energy Astrophysics
Coordinated Multiwavelength Observations of BL Lacertae in 2000
Authors:Böttcher, M.; Marscher, A.P.; Ravasio, M.; Villata, M.; Raiteri, C.M.; Aller, H.D.; Aller, M.F.; Teräsranta, H.; Mang, O.; Tagliaferri, G.; Aharonian, F.A.; Krawczynski, H.; Kurtanidze, O.M.; Nikolashvili, M.G.; Ibrahimov, M.a.; Papadakis, I.E.; Tsinganos, K.; Sadakane, K.; Okada, N.; Takalo, L.O.; Sillanpää, A.; Tosti, G.; Ciprini, S.; Frasca, A.; Marilli, E.; Robb, R.; Noble, J.C.; Jorstad, S.G.; Hagen-Thorn, V.A.; Larionov, V.M.; Nesci, R.; Maesano, M.; Schwartz, R.D.; Basler, J.; Gorham, P.W.; Iwamatsu, H.; Kato, T.; Pullen, C.; Benítez, E.; de Diego, J.A.; Moilanen, M.; Oksanen, A.; Rodriguez, D.; Sadun, A.C.; Kelly, M.; Carini, M.T.; Miller, H.R.; Catalano, S.; Dultzin-Hacyan, D.; Fan, J.H.; Ghisellini, G.; Ishioka, R.; Karttunen, H.; Keinänen, P.; Kudryavtseva, N.A.; Lainela, M.; Lanteri, L.; Larionova, E.G.; Matsumoto, K.; Mattox, J.R.; McHardy, I.; Montagni, F.; Nucciarelli, G.; Ostorero, L.; Papamastorakis, J.; Pasanen, M.; Sobrito, G.; Uemura, M.
Date of Publication (YYYY-MM-DD):2003-10-20
Title of Journal:Astrophysical Journal
Journal Abbrev.:Astrophys. J.
Issue / Number:2, Part 1
Start Page:847
End Page:859
Copyright:The American Astronomical Society
Review Status:not specified
Audience:Experts Only
Abstract / Description:BL Lacertae (BL Lac) was the target of an extensive multiwavelength monitoring campaign in the second half of 2000. Simultaneous or quasi-simultaneous observations were taken at radio (University of Michigan Radio Astronomy Observatory and Metsähovi Radio Telescope) and optical (Whole Earth Blazar Telescope [WEBT] collaboration) frequencies, in X-rays (BeppoSAX and RXTE), and at very high energy gamma rays (HEGRA). The WEBT optical campaign achieved an unprecedented time coverage, virtually continuous over several 10–20 hr segments. It revealed intraday variability on timescales of ∼1.5 hr and evidence for spectral hardening associated with increasing optical flux. During the campaign, BL Lac underwent a major transition from a rather quiescent state prior to 2000 September, to a flaring state for the rest of the year. This was also evident in the X-ray activity of the source. BeppoSAX observations on July 26–27 revealed a rather low X-ray flux and a hard spectrum, while a BeppoSAX pointing on 2000 October 31–November 2 indicated significant variability on timescales of ≲a few hours and provided evidence for the synchrotron spectrum extending out to ∼10 keV during that time. During the July 26–27 observation, there is a tantalizing, although not statistically significant, indication of a time delay of ∼4–5 hr between the BeppoSAX and the R-band light curves. Also, a low-significance detection of a time delay of 15 days between the 14.5 and 22 GHz radio light curves is reported. Several independent methods to estimate the comoving magnetic field in the source are presented, suggesting a value of ∼2e G, where eB is the magnetic field equipartition factor with respect to the electron energy density in the jet.
Free Keywords:BL Lacertae objects: individual (BL Lacertae)—galaxies: active— gamma rays: theory—radiation mechanisms: nonthermal
External Publication Status:published
Document Type:Article
Affiliations:MPI für Kernphysik/Group H. J. Völk/High Energy Astrophysics (F. Aharonian)
External Affiliations:Department of Physics and Astronomy, Clippinger 339, Ohio University, Athens, OH 45701.
Department of Astronomy, Boston University, 725 Commonwealth Avenue, Boston, MA 02215.
Osservatorio Astronomico di Brera, Via Bianchi 46, I-23807 Merate, Italy.
Istituto Nazionale di Astrofisica (INAF), Osservatorio Astronomico di Torino, Via Osservatorio 20, I-10025 Pino Torinese, Italy.
Department of Astronomy, University of Michigan, 810 Dennison Building, Ann Arbor, MI 48109-1090.
Metsähovi Radio Observatory, Helsinki University of Technology, Metsähovintie 114, 02540 Kylmälä, Finland.
Institut für Experimentelle und Angewandte Physik, Universität Kiel, Leibnitzstrasse 15–19, D-24118 Kiel, Germany.
Max-Planck-Institut für Kernphysik, Postfach 10 39 80, D-69029 Heidelberg, Germany.
Physics Department, Washington University, 1 Brookings Drive, CB 1105, St. Louis, MO 63130.
Abastumani Observatory, 383762 Abastumani, Georgia.
Astrophysikalisches Institute Potsdam, An der Sternwarte 16, D-14482 Potsdam, Germany.
Landessternwarte Heidelberg-Königstuhl, Königstuhl 12, D-69117 Heidelberg, Germany.
Ulugh Beg Astronomical Institute, Uzbek Academy of Sciences, Astronomicheskaya 33, Tashkent 700052, Uzbekistan.
Isaac Newton Institute of Chile, Uzbekistan Branch.
Physics Department, University of Crete, 710 03 Heraklion, Crete, Greece.
IESL, Foundation for Research and Technology-Hellas, 711 10 Heraklion, Crete, Greece.
Astronomical Institute, Osaka Kyoiku University, Kashiwara-shi, Osaka 582-8582, Japan.
Tuorla Observatory, 21500 Piikkiö, Finland.
Osservatorio Astronomico, Università di Perugia, Via B. Bonfigli, I-06126 Perugia, Italy.
Osservatorio Astrofisico di Catania, Viale A. Doria 6, I-95125 Catania, Italy.
Department of Physics and Astronomy, University of Victoria, BC, Canada.
Institute for Astrophysical Research, Boston University, 725 Commonwealth Avenue, Boston, MA 02215.
Center for Astrophysics, Guangzhou University, Guangzhou 510400, China.
Astronomical Institute, St. Petersburg State University, Bibliotechnaya Pl. 2, Petrodvoretz, 198504 St. Petersburg, Russia.
Dipartimento di Fisica, Università La Sapienza, Piazzale A. Moro 2, I-00185 Rome, Italy.
Department of Physics and Astronomy, University of Missouri-St. Louis, 8001 Natural Bridge Road, St. Louis, MO 63121.
Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109.
Department of Astronomy, Faculty of Science, Kyoto University, Kyoto, Japan.
Clarke and Coyote Astrophysical Observatory, P.O. Box 930, Wilton, CA 95693.
Instituto de Astronomía, UNAM, Apartado Postal 70-264, 04510 Mexico DF, Mexico.
Nyrölä Observatory, Jyväskylän Sirius ry, Kyllikinkatu 1, 40950 Jyväskylä, Finland.
Guadarrama Observatory, C/ San Pablo 5, Villalba 28409, Madrid, Spain.
Department of Physics, University of Colorado, P.O. Box 173364, Denver, CO 80217-3364.
Department of Physics and Astronomy, Western Kentucky University, 1 Big Red Way, Bowling Green, KY 42104.
Department of Physics and Astronomy, Georgia State University, Atlanta, GA 30303.
Department of Chemistry, Physics, and Astronomy, Francis Marion University, P.O. Box 100547, Florence, SC 29501-0547.
Department of Physics and Astronomy, University of Southampton Highfield, Southampton SO17 1BJ, UK.
Dipartimento di Fisica Generale, Università di Torino, Via P. Giuria 1, I-10125 Turin, Italy.
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