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Publication Details
AFRICAN RESEARCH NEXUS
SHINING A SPOTLIGHT ON AFRICAN RESEARCH
Another look at the BL Lacertae flux and spectral variability:Observations by GASP-WEBT, XMM- Newton, and Swift in 2008-2009
Astronomy and Astrophysics, Volume 524, No. 5, Article A43, Year 2010
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Description
Aims. In a previous study we suggested that the broad-band emission and variability properties of BL Lacertae can be accounted for by a double synchrotron emission component with relatedinverse-Compton emission from the jet, plus thermal radiation from the accretion disc. Here we investigate the matter with further data extending over a wider energy range. Methods. The GLAST-AGILE Support Program (GASP) of the whole earth blazar telescope (WEBT) monitored BL Lacertae in 2008-2009 at radio, near-IR, and optical frequencies to follow its flux behaviour. During this period, high-energy observations were performed by XMM-Newton, Swift, and Fermi. We analyse these data with particular attention to the calibration of Swift UV data, and apply a helical jet model to interpret the source broad-band variability. Results. The GASP-WEBT observations show an optical flare in 2008 February-March, and oscillations of several tenths of mag on a few-day time scale afterwards. The radio flux is only mildly variable. The UV data from both XMM-Newton and Swift seem to confirm a UV excess that is likely caused by thermal emission from the accretion disc. The X-ray data from XMM-Newton indicate a strongly concave spectrum, as well as moderate (∼4-7%) flux variability on an hour time scale. The Swift X-ray data reveal fast (interday) flux changes, not correlated with those observed at lower energies. We compare the spectral energy distribution (SED) corresponding to the 2008 low-brightness state, which was characterised by a synchrotron dominance, to the 1997 outburst state, where the inverse-Compton emission was prevailing. A fit with an inhomogeneous helical jet model suggests that two synchrotron components are at work with their self inverse-Compton emission. Most likely, they represent the radiation from two distinct emitting regions in the jet. We show that the difference between the source SEDs in 2008 and 1997 can be explained in terms of pure geometrical variations. The outburst state occurred when the jet-emitting regions were better aligned with the line of sight, producing an increase of the Doppler beaming factor. Conclusions. Our analysis demonstrates that the jet geometry can play an extremely important role in the BL Lacertae flux and spectral variability. Indeed, the emitting jet is probably a bent and dynamic structure, and hence changes in the emitting regions viewing angles are likely to happen, with strong consequences on the source multiwavelength behaviour. © 2010 ESO.
Authors & Co-Authors
Raiteri, Claudia M.
Italy, Rome
Istituto Nazionale Di Astrofisica, Rome
Villata, Massimo
Italy, Rome
Istituto Nazionale Di Astrofisica, Rome
Capetti, Alessandro
Italy, Rome
Istituto Nazionale Di Astrofisica, Rome
Kurtanidze, Omar M.
Unknown Affiliation
Larionov, Valeri M.
Russian Federation, Saint Petersburg
Saint Petersburg State University
Russian Federation, Saint Petersburg
Pulkovo Observatory of the Russian Academy of Sciences
Romano, P.
Italy, Palermo
Inaf Istituto Di Astrofisica Spaziale e Fisica Cosmica Di Palermo
Vercellone, Stefano
Italy, Palermo
Inaf Istituto Di Astrofisica Spaziale e Fisica Cosmica Di Palermo
Agudo, Iván N.
United States, Boston
Boston University
Spain, Madrid
Consejo Superior de Investigaciones Científicas
Aller, Hugh D.
United States, Ann Arbor
University of Michigan, Ann Arbor
Aller, M. F.
United States, Ann Arbor
University of Michigan, Ann Arbor
Arkharov, Arkady A.H.
Russian Federation, Saint Petersburg
Pulkovo Observatory of the Russian Academy of Sciences
Bach, Uwe
Germany, Bonn
Max Planck Institute for Radio Astronomy
Berdyugin, Andrei V.
Finland, Turku
Turun Yliopisto
Blinov, Dmitry A.
Russian Federation, Saint Petersburg
Saint Petersburg State University
Boettcher, M.
United States, Athens
Ohio University
Buemi, Carla S.
Italy, Catania
Osservatorio Astrofisico Di Catania
Calcidese, Paolo
Italy, Nus
Osservatorio Astronomico Della Regione Autonoma Valle D'aosta
Carosati, Daniele
Italy
Armenzano Astronomical Observatory
Casas, Ricard
Spain, Barcelona
Csic - Instituto de Ciencias Del Espacio Ice
Chen, Wenping
Taiwan, Taoyuan
National Central University
Coloma, Josep M.
Unknown Affiliation
Diltz, Chris
United States, Athens
Ohio University
Di Paola, Andrea
Italy, Rome
Istituto Nazionale Di Astrofisica, Rome
Efimova, Natalia V.
Russian Federation, Saint Petersburg
Saint Petersburg State University
Russian Federation, Saint Petersburg
Pulkovo Observatory of the Russian Academy of Sciences
Forné, E.
Unknown Affiliation
Gómez, Jose L.
Spain, Madrid
Consejo Superior de Investigaciones Científicas
Gurwell, Mark A.
United States, Cambridge
Harvard-smithsonian Center for Astrophysics
Hovatta, Talvikki
Finland, Espoo
Aalto University
United States, West Lafayette
Purdue University
Hsiao, Hsiangyao
Taiwan, Taoyuan
National Central University
Jorstad, Svetlana G.
United States, Boston
Boston University
Koptelova, Ekaterina A.
Taiwan, Taoyuan
National Central University
Kurtanidze, Sofia O.
Unknown Affiliation
L¨ahteenm¨aki, Anne A.
Finland, Espoo
Aalto University
Larionova, Elena G.
Russian Federation, Saint Petersburg
Saint Petersburg State University
Leto, Paolo
Italy, Catania
Osservatorio Astrofisico Di Catania
Lindfors, Elina J.
Finland, Turku
Turun Yliopisto
Ligustri, Rolando
Unknown Affiliation
Marscher, Alan P.
United States, Boston
Boston University
Morozova, Daria A.
Russian Federation, Saint Petersburg
Saint Petersburg State University
Nikolashvili, M. G.
Unknown Affiliation
Nilsson, Kari
Finland, Turku
Turun Yliopisto
Ros, J. A.
Unknown Affiliation
Roustazadeh, Parisa
United States, Athens
Ohio University
Sadun, Alberto C.
United States, Denver
University of Colorado Denver
Sillanp̈äa, Aimo K.
Finland, Turku
Turun Yliopisto
Takalo, Leo O.
Finland, Turku
Turun Yliopisto
Tornikoski, Merja
Finland, Espoo
Aalto University
Trigilio, Corrado
Italy, Catania
Osservatorio Astrofisico Di Catania
Troitsky, Ivan S.
Russian Federation, Saint Petersburg
Saint Petersburg State University
Umana, Grazia
Italy, Catania
Osservatorio Astrofisico Di Catania
Statistics
Citations: 69
Authors: 50
Affiliations: 21
Identifiers
Doi:
10.1051/0004-6361/201015191
ISSN:
14320746
Research Areas
Cancer
Environmental