E. Benítez

Steps toward determination of the size and structure of the broad-line region in active galactic nuclei. XI. Intensive monitoring of the ultraviolet spectrum of NGC 7469

From 1996 June 10 to July 29, the International Ultraviolet Explorer monitored the Seyfert 1 galaxy NGC 7469 continuously in an attempt to measure time delays between the continuum and emission-line fluxes. From the time delays, one can estimate the size of the region dominating the production of the UV emission lines in this source. We find the strong UV emission lines to respond to continuum variations with time delays of about 23-31 for Lyα, 27 for C IV λ1549, 19-24 for N V λ1240, 17-18 for Si IV λ1400, and 07-10 for He II λ1640. The most remarkable result, however, is the detection of apparent time delays between the different UV continuum bands. With respect to the UV continuum flux at 1315 A, the flux at 1485 A, 1740 A, and 1825 A lags with time delays of 021, 035, and 028, respectively. Determination of the significance of this detection is somewhat problematic since it depends on accurate estimation of the uncertainties in the lag measurements, which are difficult to assess. We attempt to estimate the uncertainties in the time delays through Monte Carlo simulations, and these yield estimates of ~007 for the 1 σ uncertainties in the interband continuum time delays. Possible explanations for the delays include the existence of a continuum-flux reprocessing region close to the central source and/or a contamination of the continuum flux with a very broad time-delayed emission feature such as the Balmer continuum or merged Fe II multiplets.

The unprecedented optical outburst of the quasar 3C 454.3 : The WEBT campaign of 2004-2005

Context. The radio quasar 3C 454.3 underwent an exceptional optical outburst lasting more than 1 year and culminating in spring 2005. The maximum brightness detected was

Coordinated Multiwavelength Observations of BL Lacertae in 2000

R=12.0

The GASP-WEBT monitoring of 3C 454.3 during the 2008 optical-to-radio and γ-ray outburst

, which represents the most luminous quasar state thus far observed (

A Comparative Study of the Microvariability Properties in Radio-loud and Radio-quiet Quasars

M_B \sim -31.4

WEBT multiwavelength monitoring and XMM-Newton observations of BL Lacertae in 2007-2008 Unveiling different emission components

). Aims. In order to follow the emission behaviour of the source in detail, a large multiwavelength campaign was organized by the Whole Earth Blazar Telescope (WEBT). Methods. Continuous optical, near-IR and radio monitoring was performed in several bands. ToO pointings by the Chandra and INTEGRAL satellites provided additional information at high energies in May 2005. Results. The historical radio and optical light curves show different behaviours. Until about 2001.0 only moderate variability was present in the optical regime, while prominent and long-lasting radio outbursts were visible at the various radio frequencies, with higher-frequency variations preceding the lower-frequency ones. After that date, the optical activity increased and the radio flux is less variable. This suggests that the optical and radio emissions come from two separate and misaligned jet regions, with the inner optical one acquiring a smaller viewing angle during the 2004-2005 outburst. Moreover, the colour-index behaviour (generally redder-when-brighter) during the outburst suggests the presence of a luminous accretion disc. A huge mm outburst followed the optical one, peaking in June-July 2005. The high-frequency (37-43 GHz) radio flux started to increase in early 2005 and reached a maximum at the end of our observing period (end of September 2005). VLBA observations at 43 GHz during the summer confirm the brightening of the radio core and show an increasing polarization. An exceptionally bright X-ray state was detected in May 2005, corresponding to the rising mm flux and suggesting an inverse-Compton nature of the hard X-ray spectrum. Conclusions. A further multifrequency monitoring effort is needed to follow the next phases of this unprecedented event.

Coordinated Multiwavelength Observation of 3C 66A during the WEBT Campaign of 2003-2004*

BL Lacertae (BL Lac) was the target of an extensive multiwavelength monitoring campaign in the second half of 2000. Simultaneous or quasi-simultaneous observations were taken at radio (University of Michigan Radio Astronomy Observatory and Metsahovi Radio Telescope) and optical (Whole Earth Blazar Telescope (WEBT) collaboration) frequencies, in X-rays (BeppoSAX and RXTE), and at very high energy gamma rays (HEGRA). The WEBT optical campaign achieved an unprecedented time coverage, virtually continuous over several 10-20 hr segments. It revealed intraday variability on timescales of � 1.5 hr and evidence for spectral hardening associated with increasing optical flux. During the campaign, BL Lac underwent a major transition from a rather quiescent state prior to 2000 September, to a flaring state for the rest of the year. ThisBL Lacertae (BL Lac) was the target of an extensive multiwavelength monitoring campaign in the second half of 2000. Simultaneous or quasi-simultaneous observations were taken at radio (University of Michigan Radio Astronomy Observatory andMetsähovi Radio Telescope) and optical (Whole Earth Blazar Telescope [WEBT] collaboration) frequencies, in X-rays (BeppoSAX and RXTE), and at very high energy gamma rays (HEGRA). The WEBT optical campaign achieved an unprecedented time coverage, virtually continuous over several 10–20 hr segments. It revealed intraday variability on timescales of 1.5 hr and evidence for spectral hardening associated with increasing optical flux. During the campaign, BL Lac underwent a major transition from a rather quiescent state prior to 2000 September, to a flaring state for the rest of the year. This 36 Department of Chemistry, Physics, and Astronomy, FrancisMarionUniversity, P.O. Box 100547, Florence, SC 29501-0547. 37 Department of Physics and Astronomy, University of SouthamptonHighfield, Southampton SO17 1BJ, UK. 38 Dipartimento di Fisica Generale, Università di Torino, Via P. Giuria 1, I-10125 Turin, Italy. 34 Department of Physics and Astronomy,Western KentuckyUniversity, 1 Big RedWay, Bowling Green, KY 42104. 35 Department of Physics and Astronomy, Georgia State University, Atlanta, GA 30303. 1 Department of Physics and Astronomy, Clippinger 339, Ohio University, Athens, OH 45701. 2 Department of Astronomy, BostonUniversity, 725 Commonwealth Avenue, Boston,MA 02215. 3 Osservatorio Astronomico di Brera, Via Bianchi 46, I-23807Merate, Italy. 4 IstitutoNazionale di Astrofisica (INAF), Osservatorio Astronomico di Torino, Via Osservatorio 20, I-10025 Pino Torinese, Italy. 5 Department of Astronomy, University ofMichigan, 810 Dennison Building, AnnArbor,MI 48109-1090. 6 Metsähovi Radio Observatory, Helsinki University of Technology,Metsähovintie 114, 02540Kylmälä, Finland. 7 Institut für Experimentelle und Angewandte Physik, Universität Kiel, Leibnitzstrasse 15–19, D-24118Kiel, Germany. 8 Max-Planck-Institut für Kernphysik, Postfach 10 39 80, D-69029Heidelberg, Germany. 9 Physics Department,WashingtonUniversity, 1 Brookings Drive, CB 1105, St. Louis, MO 63130. 10 Abastumani Observatory, 383762Abastumani, Georgia. 11 Astrophysikalisches Institute Potsdam, An der Sternwarte 16, D-14482 Potsdam, Germany. 12 Landessternwarte Heidelberg-Königstuhl, Königstuhl 12, D-69117Heidelberg, Germany. 13 Ulugh Beg Astronomical Institute, Uzbek Academy of Sciences, Astronomicheskaya 33, Tashkent 700052, Uzbekistan. 14 IsaacNewton Institute of Chile, Uzbekistan Branch. 15 Physics Department, University of Crete, 710 03Heraklion, Crete, Greece. 16 IESL, Foundation for Research and Technology-Hellas, 711 10Heraklion, Crete, Greece. 17 Astronomical Institute, OsakaKyoikuUniversity, Kashiwara-shi, Osaka 582-8582, Japan. 18 Tuorla Observatory, 21500 Piikkiö, Finland. 19 Osservatorio Astronomico, Università di Perugia, Via B. Bonfigli, I-06126 Perugia, Italy. 20 Osservatorio Astrofisico di Catania, Viale A. Doria 6, I-95125 Catania, Italy. 21 Department of Physics and Astronomy, University of Victoria, BC, Canada. 22 Institute for Astrophysical Research, BostonUniversity, 725 Commonwealth Avenue, Boston,MA 02215. 23 Center for Astrophysics, GuangzhouUniversity, Guangzhou 510400, China. 24 Astronomical Institute, St. Petersburg State University, Bibliotechnaya Pl. 2, Petrodvoretz, 198504 St. Petersburg, Russia. 25 Dipartimento di Fisica, Università La Sapienza, Piazzale A.Moro 2, I-00185Rome, Italy. 26 Department of Physics and Astronomy, University ofMissouri-St. Louis, 8001 Natural Bridge Road, St. Louis,MO 63121. 27 Jet Propulsion Laboratory, California Institute of Technology, 4800 OakGroveDrive, Pasadena, CA 91109. 28 Department of Astronomy, Faculty of Science, KyotoUniversity, Kyoto, Japan. 29 Clarke and Coyote Astrophysical Observatory, P.O. Box 930,Wilton, CA 95693. 30 Instituto de Astronomı́a, UNAM,Apartado Postal 70-264, 04510MexicoDF,Mexico. 31 Nyrölä Observatory, Jyväskylän Sirius ry, Kyllikinkatu 1, 40950 Jyväskylä, Finland. 32 GuadarramaObservatory, C/ San Pablo 5, Villalba 28409,Madrid, Spain. 33 Department of Physics, University of Colorado, P.O. Box 173364, Denver, CO 80217-3364. The Astrophysical Journal, 596:847–859, 2003 October 20 # 2003. The American Astronomical Society. All rights reserved. Printed in U.S.A. E

The long-lasting activity of 3C 454.3 - GASP-WEBT and satellite observations in 2008–2010

Context. Since 2001, the radio quasar 3C 454.3 has undergone a period of high optical activity, culminating in the brightest optical state ever observed, during the 2004-2005 outburst. The Whole Earth Blazar Telescope (WEBT) consortium has carried out several multifrequency campaigns to follow the source behaviour. Aims. The GLAST-AGILE Support Program (GASP) was born from the WEBT to provide long-term continuous optical-to-radio monitoring of a sample of γ -loud blazars, during the operation of the AGILE and GLAST (now known as Fermi GST) γ -ray satellites. The main aim is to shed light on the mechanisms producing the high-energy radiation, through correlation analysis with the low-energy emission. Thus, since 2008 the monitoring task on 3C 454.3 passed from the WEBT to the GASP, while both AGILE and Fermi detected strong γ -ray emission from the source. Methods. We present the main results obtained by the GASP at optical, mm, and radio frequencies in the 2008-2009 season, and compare them with the WEBT results from previous years. Results. An optical outburst was observed to peak in mid July 2008, when Fermi detected the brightest γ -ray levels. A contemporaneous mm outburst maintained its brightness for a longer time, until the cm emission also reached the maximum levels. The behaviour compared in the three bands suggests that the variable relative brightness of the different-frequency outbursts may be due to the changing orientation of a curved inhomogeneous jet. The optical light curve is very well sampled during the entire season, which is also well covered by the various AGILE and Fermi observing periods. The relevant cross-correlation studies will be very important in constraining high-energy emission models.

The awakening of BL Lacertae: observations by Fermi, Swift and the GASP-WEBT

We have performed photometric optical observations of a sample of 17 core-dominated radio-loud quasars (CRLQs) and 17 radio-quiet quasars (RQQs). The aims were to confirm the existence of microvariations in strictly radio-quiet objects and to compare the properties of the variations in both types of quasars. Great care was taken to avoid selection effects and spurious biases in the samples. We present a new observational and statistical procedure for searching for microvariability, based on the analysis of variance. The results show that microvariations in RQQs may be as frequent as in CRLQs. The implications for the physical models for microvariations are briefly discussed.

Variability of the blazar 4C 38.41 (B3 1633+382) from GHz frequencies to GeV energies

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.