WEBT multiwavelength monitoring and XMM-Newton observations of BL Lacertae in 2007-2008
Journal
Date Issued
2009
Author(s)
•
•
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Aller, M.F.
•
Bach, U.
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Calcidese, P.
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Gurwell, M.A.
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Larionov, V.M.
•
Ohlert, J.
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Nilsson, K.
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Strigachev, A.
•
Agudo, I.
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Aller, H.D.
•
Bachev, R.
•
Benítez, E.
•
Berdyugin, A.
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Böttcher, M.
•
•
Buttiglione, S.
•
Carosati, D.
•
Charlot, P.
•
Chen, W.P.
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Dultzin, D.
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Forné, E.
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Fuhrmann, L.
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Gómez, J.L.
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Gupta, A.C.
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Heidt, J.
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Hiriart, D.
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Hsiao, W.-S.
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Jelínek, M.
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Jorstad, S.G.
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Kimeridze, G.N.
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Konstantinova, T.S.
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Kopatskaya, E.N.
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Kostov, A.
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Kurtanidze, O.M.
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Lähteenmäki, A.
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Larionova, L.V.
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Latev, G.
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Le Campion, J.-F.
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Lee, C.-U.
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Ligustri, R.
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Lindfors, E.
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Marscher, A.P.
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Mihov, B.
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Nikolashvili, M.G.
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Nikolov, Y.
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Ovcharov, E.
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Principe, D.
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Pursimo, T.
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Ragozzine, B.
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Robb, R.M.
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Ros, J.A.
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Sadun, A.C.
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Sagar, R.
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Semkov, E.
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Sigua, L.A.
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Sorcia, M.
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Takalo, L.O.
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Tornikoski, M.
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Uckert, K.
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Valcheva, A.
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Volvach, A.
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.
Volume
507
Issue
2
Start page
769
Issn Identifier
0004-6361
Ads BibCode
2009A&A...507..769R
Rights
open.access
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