1. WEBT multiwavelength monitoring and XMM-Newton observations of BL Lacertae in 2007-2008. Unveiling different emission components
- Author
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C. M. Raiteri, M. Villata, A. Capetti, M. F. Aller, U. Bach, P. Calcidese, M. A. Gurwell, V. M. Larionov, J. Ohlert, K. Nilsson, A. Strigachev, I. Agudo, H. D. Aller, R. Bachev, E. Benítez, A. Berdyugin, M. Böttcher, C. S. Buemi, S. Buttiglione, D. Carosati, P. Charlot, W. P. Chen, D. Dultzin, E. Forné, L. Fuhrmann, J. L. Gómez, A. C. Gupta, J. Heidt, D. Hiriart, W.-S. Hsiao, M. Jelínek, S. G. Jorstad, G. N. Kimeridze, T. S. Konstantinova, E. N. Kopatskaya, A. Kostov, O. M. Kurtanidze, A. Lähteenmäki, L. Lanteri, L. V. Larionova, P. Leto, G. Latev, J.-F. Le Campion, C.-U. Lee, R. Ligustri, E. Lindfors, A. P. Marscher, B. Mihov, M. G. Nikolashvili, Y. Nikolov, E. Ovcharov, D. Principe, T. Pursimo, B. Ragozzine, R. M. Robb, J. A. Ros, A. C. Sadun, R. Sagar, E. Semkov, L. A. Sigua, R. L. Smart, M. Sorcia, L. O. Takalo, M. Tornikoski, C. Trigilio, K. Uckert, G. Umana, A. Valcheva, A. Volvach, INAF - Osservatorio Astrofisico di Torino (OATo), Istituto Nazionale di Astrofisica (INAF), Instituto de Neurociencias de Alicante, Universidad Miguel Hernández [Elche] (UMH), Laboratoire d'astrodynamique, d'astrophysique et d'aéronomie de bordeaux (L3AB), Université Sciences et Technologies - Bordeaux 1-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), Observatoire aquitain des sciences de l'univers (OASU), Laboratoire d'Astrophysique de Bordeaux [Pessac] (LAB), and Université de Bordeaux (UB)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)
- Subjects
Brightness ,[PHYS.ASTR.HE]Physics [physics]/Astrophysics [astro-ph]/High Energy Astrophysical Phenomena [astro-ph.HE] ,Cosmology and Nongalactic Astrophysics (astro-ph.CO) ,Astrophysics::High Energy Astrophysical Phenomena ,FOS: Physical sciences ,Astrophysics ,Astrophysics::Cosmology and Extragalactic Astrophysics ,01 natural sciences ,Power law ,Spectral line ,Luminosity ,law.invention ,Telescope ,law ,0103 physical sciences ,Blazar ,010303 astronomy & astrophysics ,Astrophysics::Galaxy Astrophysics ,High Energy Astrophysical Phenomena (astro-ph.HE) ,Physics ,Line-of-sight ,010308 nuclear & particles physics ,Molecular cloud ,[SDU.ASTR.HE]Sciences of the Universe [physics]/Astrophysics [astro-ph]/High Energy Astrophysical Phenomena [astro-ph.HE] ,Astronomy and Astrophysics ,Space and Planetary Science ,Astrophysics - High Energy Astrophysical Phenomena ,Astrophysics - Cosmology and Nongalactic Astrophysics - Abstract
In 2007-2008 we carried out a new multiwavelength campaign of the Whole Earth Blazar Telescope (WEBT) on BL Lacertae, involving three pointings by the XMM-Newton satellite, to study its emission properties. The source was monitored in the optical-to-radio bands by 37 telescopes. The brightness level was relatively low. Some episodes of very fast variability were detected in the optical bands. The X-ray spectra are well fitted by a power law with photon index of about 2 and photoelectric absorption exceeding the Galactic value. However, when taking into account the presence of a molecular cloud on the line of sight, the data are best fitted by a double power law, implying a concave X-ray spectrum. The spectral energy distributions (SEDs) built with simultaneous radio-to-X-ray data at the epochs of the XMM-Newton observations suggest that the peak of the synchrotron emission lies in the near-IR band, and show a prominent UV excess, besides a slight soft-X-ray excess. A comparison with the SEDs corresponding to previous observations with X-ray satellites shows that the X-ray spectrum is extremely variable. We ascribe the UV excess to thermal emission from the accretion disc, and the other broad-band spectral features to the presence of two synchrotron components, with their related SSC emission. We fit the thermal emission with a black body law and the non-thermal components by means of a helical jet model. The fit indicates a disc temperature greater than 20000 K and a luminosity greater than 6 x 10^44 erg/s., 11 pages, 7 figures, accepted for publication in A&A
- Published
- 2009