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Title:
The WEBT campaign to observe AO 0235+16 in the 2003-2004 observing season. Results from radio-to-optical monitoring and XMM-Newton observations
Authors:
Raiteri, C. M.; Villata, M.; Ibrahimov, M. A.; Larionov, V. M.; Kadler, M.; Aller, H. D.; Aller, M. F.; Kovalev, Y. Y.; Lanteri, L.; Nilsson, K.; Papadakis, I. E.; Pursimo, T.; Romero, G. E.; Teräsranta, H.; Tornikoski, M.; Arkharov, A. A.; Barnaby, D.; Berdyugin, A.; Böttcher, M.; Byckling, K.; Carini, M. T.; Carosati, D.; Cellone, S. A.; Ciprini, S.; Combi, J. A.; Crapanzano, S.; Crowe, R.; di Paola, A.; Dolci, M.; Fuhrmann, L.; Gu, M.; Hagen-Thorn, V. A.; Hakala, P.; Impellizzeri, V.; Jorstad, S.; Kerp, J.; Kimeridze, G. N.; Kovalev, Yu. A.; Kraus, A.; Krichbaum, T. P.; Kurtanidze, O. M.; Lähteenmäki, A.; Lindfors, E.; Mingaliev, M. G.; Nesci, R.; Nikolashvili, M. G.; Ohlert, J.; Orio, M.; Ostorero, L.; Pasanen, M.; Pati, A.; Poteet, C.; Ros, E.; Ros, J. A.; Shastri, P.; Sigua, L. A.; Sillanpää, A.; Smith, N.; Takalo, L. O.; Tosti, G.; Vasileva, A.; Wagner, S. J.; Walters, R.; Webb, J. R.; Wills, W.; Witzel, A.; Xilouris, E.
Affiliation:
AA(INAF - Osservatorio Astronomico di Torino, Italy, ), AB(INAF - Osservatorio Astronomico di Torino, Italy), AC(Ulugh Beg Astronomical Inst., Uzbekistan), AD(Astronomical Inst., St.-Petersburg State Univ., Russia ; Isaac Newton Inst. of Chile, St. Petersburg Branch), AE(Max-Planck-Institut für Radioastronomie, Germany), AF(Dept. of Astronomy, Univ. of Michigan, USA), AG(Dept. of Astronomy, Univ. of Michigan, USA), AH(National Radio Astronomy Observatory, Green Bank, USA ; Astro Space Center of Lebedev Physical Inst., Russia), AI(INAF - Osservatorio Astronomico di Torino, Italy), AJ(Tuorla Astronomical Observatory, Finland), AK(IESL, FORTH, Greece ; Physics Dept., Univ. of Crete, Greece), AL(Nordic Optical Telescope, Santa Cruz de La Palma, Spain), AM(Inst. Argentino de Radioastronomía, Argentina), AN(Metsähovi Radio Observatory, Helsinki Univ. of Technology, Finland), AO(Metsähovi Radio Observatory, Helsinki Univ. of Technology, Finland), AP(Pulkovo Observatory, Russia), AQ(Dept. of Physics & Astronomy, Western Kentucky Univ., USA), AR(Tuorla Astronomical Observatory, Finland), AS(Dept. of Physics and Astronomy, Ohio Univ., USA), AT(Observatory, Univ. of Helsinki, Finland), AU(Dept. of Physics & Astronomy, Western Kentucky Univ., USA), AV(Armenzano Astronomical Observatory, Italy), AW(Facultad de Ciencias Astronómicas y Geofísicas, Argentina), AX(Tuorla Astronomical Observatory, Finland), AY(Inst. Argentino de Radioastronomía, Argentina ; Dept. de Física, Escuela Politécnica Superior, Univ. de Jaén, Spain), AZ(INAF - Osservatorio Astronomico di Torino, Italy), BA(Dept. of Physics & Astronomy, Univ. of Hawaii, USA), BB(INAF - Osservatorio Astronomico di Roma, Italy), BC(INAF - Osservatorio Astronomico di Collurania Teramo, Italy), BD(INAF - Osservatorio Astronomico di Torino, Italy; Max-Planck-Institut für Radioastronomie, Germany ; Osservatorio Astronomico, Univ. di Perugia, Italy), BE(Korea Astronomy Observatory, Korea), BF(Astronomical Inst., St.-Petersburg State Univ., Russia ; Isaac Newton Inst. of Chile, St. Petersburg Branch), BG(Observatory, Univ. of Helsinki, Finland), BH(Max-Planck-Institut für Radioastronomie, Germany), BI(Inst. for Astrophysical Research, Boston Univ., USA), BJ(Max-Planck-Institut für Radioastronomie, Germany), BK(Abastumani Observatory, Georgia), BL(Astro Space Center of Lebedev Physical Inst., Russia), BM(Max-Planck-Institut für Radioastronomie, Germany), BN(Max-Planck-Institut für Radioastronomie, Germany), BO(Abastumani Observatory, Georgia), BP(Metsähovi Radio Observatory, Helsinki Univ. of Technology, Finland), BQ(Tuorla Astronomical Observatory, Finland), BR(Special Astrophysical Observatory, Karachaevo-Cherkessia, Russia), BS(Dipartimento di Fisica, Univ. di Roma “La Sapienza”, Italy), BT(Abastumani Observatory, Georgia), BU(Michael Adrian Observatory, Trebur, Germany), BV(INAF - Osservatorio Astronomico di Torino, Italy), BW(Landessternwarte Heidelberg, Germany), BX(Tuorla Astronomical Observatory, Finland), BY(Indian Inst. of Astrophysics, Bangalore, India), BZ(Dept. of Physics & Astronomy, Western Kentucky Univ., USA), CA(Max-Planck-Institut für Radioastronomie, Germany), CB(Agrupació Astronòmica de Sabadell, Spain), CC(Indian Inst. of Astrophysics, Bangalore, India), CD(Abastumani Observatory, Georgia), CE(Tuorla Astronomical Observatory, Finland), CF(Dept. of Applied Physics & Instrumentation, Cork Inst. of Technology, Ireland), CG(Tuorla Astronomical Observatory, Finland), CH(Osservatorio Astronomico, Univ. di Perugia, Italy), CI(Astronomical Inst., St.-Petersburg State Univ., Russia), CJ(Landessternwarte Heidelberg, Germany), CK(Dept. of Physics & Astronomy, Western Kentucky Univ., USA), CL(SARA Observatory, Florida International Univ., USA), CM(Dept. of Physics & Astronomy, Western Kentucky Univ., USA), CN(Max-Planck-Institut für Radioastronomie, Germany), CO(Inst. of Astronomy and Astrophysics, National Observatory of Athens, Greece)
Publication:
Astronomy and Astrophysics, Volume 438, Issue 1, July IV 2005, pp.39-53 (A&A Homepage)
Publication Date:
07/2005
Origin:
EDP Sciences
Keywords:
galaxies: active, BL Lacertae objects: general, BL Lacertae objects: individual: AO 0235+16
DOI:
10.1051/0004-6361:20042567
Bibliographic Code:
2005A&A...438...39R

Abstract

A multiwavelength campaign to observe the BL Lac object AO 0235+16 (z=0.94) was set up by the Whole Earth Blazar Telescope (WEBT) collaboration during the observing seasons 2003-2004 and 2004-2005, involving radio, near-IR and optical photometric monitoring, VLBA monitoring, optical spectral monitoring, and three pointings by the XMM-Newton satellite. Here we report on the results of the first season, which involved the participation of 24 optical and near-IR telescopes and 4 radio telescopes, as well as the first XMM-Newton pointing, which occurred on January 18-19, 2004. Unpublished data from previous epochs were also collected (from 5 optical-NIR and 3 radio telescopes), in order to fill the gap between the end of the period presented in Raiteri et al. (2001) and the start of the WEBT campaign. The contribution of the southern AGN, 2 arcsec distant from the source, is taken into account. It is found to especially affect the blue part of the optical spectrum when the source is faint. In the optical and near-IR the source has been very active in the last 3 years, although it has been rather faint most of the time, with noticeable variations of more than a magnitude over a few days. In contrast, in the radio bands it appears to have been “quiescent” since early 2000. The major radio (and optical) outburst predicted to peak around February-March 2004 (with a six month uncertainty) has not occurred yet. When comparing our results with the historical light curves, two different behaviours seem to characterize the optical outbursts: only the major events present a radio counterpart. The X-ray spectra obtained by the three EPIC detectors are well fitted by a power law with extra-absorption at z=0.524; the energy index in the 0.2-10 keV range is well constrained: α=0.645 ± 0.028 and the 1 keV flux density is 0.311 ± 0.008~μ Jy. The analysis of the X-ray light curves reveals that no significant variations occurred during the pointing. In contrast, simultaneous dense radio monitoring with the 100 m telescope at Effelsberg shows a ~2-3% flux decrease in 6-7 h, which, if intrinsic, would imply a brightness temperature well above the Compton limit and hence a lower limit to the Doppler factor δ ⪆ 46. We construct the broad-band spectral energy distribution of January 18-19, 2004 with simultaneous radio data from Effelsberg, optical data from the Nordic Optical Telescope (NOT), optical-UV data from the Optical Monitor onboard XMM-Newton, and X-ray data by the EPIC instruments. Particular care is taken to correct data for extinction due to both the Milky Way and the z=0.524 absorber. The resulting SED suggests the existence of a bump in the UV spectral region.
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