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          Institute: MPI für Radioastronomie     Collection: Publikationen des MPI für Radioastronomie     Display Documents



ID: 125464.0, MPI für Radioastronomie / Publikationen des MPI für Radioastronomie
Optical and radio behaviour of the BL Lacertae object 0716+714
Authors:Raiteri, C. M.; Villata, M.; Tosti, G.; Nesci, R.; Massaro, E.; Aller, M. F.; Aller, H. D.; Terasranta, H.; Kurtanidze, O. M.; Nikolashvili, M. G.; Ibrahimov, M. A.; Papadakis, I. E.; Krichbaum, T. P.; Kraus, A.; Witzel, A.; Ungerechts, H.; Lisenfeld, U.; Bach, U.; Cimo, G.; Ciprini, S.; Fuhrmann, L.; Kimeridze, G. N.; Lanteri, L.; Maesano, M.; Montagni, F.; Nucciarelli, G.; Ostorero, L.
Language:English
Date of Publication (YYYY-MM-DD):2003-04
Title of Journal:Astronomy & Astrophysics
Journal Abbrev.:Astron. Astrophys.
Volume:402
Issue / Number:1
Start Page:151
End Page:169
Review Status:Peer-review
Audience:Experts Only
Abstract / Description:Eight optical and four radio observatories have been intensively monitoring the BL Lac object 0716+714 in the last years: 4854 data points have been collected in the UBVRI bands since 1994, while radio light curves extend back to 1978. Many of these data, which all together constitute the widest optical and radio database available on this object, are presented here for the first time. Four major optical outbursts were observed at the beginning of 1995, in late 1997, at the end of 2000, and in fall 2001. In particular, an exceptional brightening of 2.3 mag in 9 days was detected in the R band just before the BeppoSAX pointing of October 30, 2000. A big radio outburst lasted from early 1998 to the end of 1999. The long-term trend shown by the optical light curves seems to vary with a characteristic time scale of about 3.3 years, while a longer period of 5.5-6 years seems to characterize the radio long-term variations. In general, optical colour indices are only weakly correlated with brightness; a clear spectral steepening trend was observed during at least one long-lasting dimming phase. Moreover, the optical spectrum became steeper after JDsimilar to2451000, the change occurring in the decaying phase of the late-1997 outburst. The radio flux behaviour at different frequencies is similar, but the flux variation amplitude decreases with increasing wavelength. The radio spectral index varies with brightness (harder when brighter), but the radio fluxes seem to be the sum of two different-spectrum contributions: a steady base level and a harder-spectrum variable component. Once the base level is removed, the radio variations appear as essentially achromatic, similarly to the optical behaviour. Flux variations at the higher radio frequencies lead the lower-frequency ones with week-month time scales. The behaviour of the optical and radio light curves is quite different, the broad radio outbursts not corresponding in time to the faster optical ones and the cross-correlation analysis indicating only weak correlation with long time lags. However, minor radio flux enhancements simultaneous with the major optical flares can be recognized, which may imply that the mechanism producing the strong flux increases in the optical band also marginally affects the radio one. On the contrary, the process responsible for the big radio outbursts does not seem to affect the optical emission.
Free Keywords:galaxies : active, BL Lacertae objects : general, BL Lacertae objects : individual : S5 0716+71, quasars : general
Comment of the Author/Creator:Date: 2003, APR
External Publication Status:published
Document Type:Article
Communicated by:N. N.
Affiliations:MPI für Radioastronomie
External Affiliations:Osserv Astron Torino, Ist Nazl Astrofis, I-10025 Pino Torinese, TO, Italy.; Univ Perugia, Osservatorio Astron, I-06126 Perugia, Italy.; Univ Roma La Sapienza, Dipartimento Fis, I-00185 Rome, Italy.; Univ Michigan, Dept Astron, Ann Arbor, MI 48109 USA.; Metsahovi Radio Observ, Kylmala 02540, Finland.; Abastumani Observ, GE-383762 Abastumani, Rep of Georgia.; Inst Astrophys, D-14482 Potsdam, Germany.; Landessternwarte Heidelberg Konigstuhl, D-69117 Heidelberg, Germany.; Uzbek Acad Sci, Ulugh Beg Astron Inst, Tashkent 700052, Uzbekistan.; Isaac Newton Inst Chile, Uzbekistan Branch, Tashkent, Uzbekistan.; Univ Crete, Dept Phys, Iraklion 71003, Crete, Greece.; IESL, Fdn Res & Technol Hellas, Iraklion 71110, Crete, Greece.; Max Planck Inst Radioastron, D-53121 Bonn, Germany.; IRAM, E-18012 Granada, Spain.; Vallinfreda Astron Stn, Vallinfreda, RM, Italy.; Univ Turin, Dipartimento Fis Gen, I-10125 Turin, Italy.
Identifiers:ISI:000182128200017 [ID No:1]
ISSN:0004-6361 [ID No:2]
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