Blazar Times - No. 68 - May 2005
The Blazar Times
A Research Newsletter Dedicated to the BL Lac and Blazar Phenomena
No. 68 - May 2005 Editor: Travis A. Rector (


Journal Abstracts 1
Abstract Guidelines 4

Journal Abstracts
XMM-Newton View of PKS 2155-304: Characterizing the X-ray Variability Properties with EPIC-PN
Y.H. Zhang1, A. Treves2, A. Celotti3, Y.P. Qin4  and J.M. Bai4
1 Department of Physics and Tsinghua Center for Astrophysics (THCA), Tsinghua University, Beijing 100084, P.R. China
2 Dipartimento di Scienze, Università degli Studi dell'Insubria, via Valleggio 11, I-22100 Como, Italy
3 International School for Advanced Studies, SISSA/ISAS, via Beirut 2-4, I-34014 Trieste, Italy
4 National Astronomical Observatories/Yunnan Observatory, Chinese Academy of Sciences, P. O. Box 110, Kunming, Yunnan, 650011, P. R. China
Starting from XMM-Newton EPIC-PN data, we present the X-ray variability characteristics of PKS 2155-304 using a simple analysis of the excess variance, sXS2, and of the fractional rms variability amplitude, Fvar. The scatter in sXS2 and Fvar, calculated using 500 s long segments of the light curves, is smaller than the scatter expected for red noise variability. This alone does not imply that the underlying process responsible for the variability of the source is stationary, since the real changes of the individual variance estimates are possibly smaller than the large scatters expected for a red noise process. In fact the averaged sXS2 and Fvar, reducing the fluctuations of the individual variances, change with time, indicating non-stationary variability. Moreover, both the averaged sXS (absolute rms variability amplitude) and Fvar show linear correlation with source flux but in an opposite sense: sXS correlates with flux, but Fvar anti-correlates with flux. These correlations suggest that the variability process of the source is strongly non-stationary as random scatters of variances should not yield any correlation. Fvar spectra were constructed to compare variability amplitudes in different energy bands. We found that the fractional rms variability amplitude of the source, when significant variability is observed, increases logarithmically with the photon energy, indicating significant spectral variability. The point-to-point variability amplitude may also track this trend, suggesting that the slopes of the power spectral density of the source are energy-independent. Using the normalized excess variance the black hole mass of PKS 2155-304 was estimated to be about 1.45 ×108 M\bigodot. This is compared and contrasted with the estimates derived from measurements of the host galaxies.
Accepted by ApJ
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The WEBT campaign to observe AO 0235+16 in the 2003-2004 observing season.
Results from radio-to-optical monitoring and XMM-Newton observations.
C. M. Raiteri 1, M. Villata 1, M. A. Ibrahimov 2, V. M. Larionov 3,4, M. Kadler 5, H .D. Aller 6, M. F. Aller 6, Y. Y. Kovalev 7,8, L. Lanteri 1, K. Nilsson 9, I. E. Papadakis 10,11, T. Pursimo 12, G. E. Romero 13, H. Teräsranta 14, M. Tornikoski 14, A. A. Arkharov 15, D. Barnaby 16, A. Berdyugin 9, M. Böttcher 17, K. Byckling 18, M. T. Carini 16, D. Carosati 19, S. A. Cellone 20, S. Ciprini 9, J. A. Combi 13,21, S. Crapanzano 1, R. Crowe 22, A. Di Paola 23, M. Dolci 24, L. Fuhrmann 1,5,25, M. Gu 26, V. A. Hagen-Thorn 3,4, P. Hakala 18, V. Impellizzeri 5, S. Jorstad 27, J. Kerp 5, G. N. Kimeridze 28, Yu. A. Kovalev 8, A. Kraus 5, T. P. Krichbaum 5, O. M. Kurtanidze 28, A. Lähteenmäki 14, E. Lindfors 9, M. G. Mingaliev 29, R. Nesci 30, M. G. Nikolashvili 28, J. Ohlert 31, M. Orio 1, L. Ostorero 32, M. Pasanen 9, A. Pati 33, C. Poteet 16, E. Ros 5, J. A. Ros 34, P. Shastri 33, L. A. Sigua 28, A. Sillanpää 9, N. Smith 35, L. O. Takalo 9, G. Tosti 25, A. Vasileva 3, S. J. Wagner 32, R. Walters 16, J. R. Webb 36, W. Wills 16, A. Witzel 5, E. Xilouris 37
1 INAF, Osservatorio Astronomico di Torino, 10025 Pino Torinese (TO), Italy
2 Ulugh Beg Astronomical Inst., Academy of Sciences of Uzbekistan, Tashkent 700052, Uzbekistan
3 Astronomical Inst., St.-Petersburg State Univ., 198504 St.-Petersburg, Russia
4 Isaac Newton Inst. of Chile, St.-Petersburg Branch, Russia
5 Max-Planck-Institut für Radioastronomie, 53121 Bonn, Germany
6 Dept. of Astronomy, Univ. of Michigan, Ann Arbor, MI 48109, USA
7 National Radio Astronomy Observatory, Green Bank, WV 24944, USA
8 Astro Space Center of Lebedev Physical Inst., Moscow, 117997, Russia
9 Tuorla Astronomical Observatory, Univ. of Turku, 21500 Piikkiö, Finland
10 IESL, FORTH, 711 10 Heraklion, Crete, Greece
11 Physics Dept., Univ. of Crete, 710 03 Heraklion, Crete, Greece
12 Nordic Optical Telescope, 38700 Santa Cruz de La Palma, Spain
13 Inst. Argentino de Radioastronomía, Buenos Aires, Argentina
14 Metsähovi Radio Observatory, Helsinki Univ. of Technology, 02540 Kylmälä, Finland
15 Pulkovo Observatory, St.Petersburg, Russia
16 Dept. of Physics & Astronomy, Western Kentucky Univ., Bowling Green, KY 42104, USA
17 Dept. of Physics and Astronomy, Ohio Univ., Athens, OH 45701-2979, USA
18 Observatory, 00014 Univ. of Helsinki, Finland
19 Armenzano Astronomical Observatory, Assisi, Italy
20 Facultad de Ciencias Astronómicas y Geofísicas, UNLP, Buenos Aires, Argentina
21 Dept. de Física, Escuela Politécnica Superior, Univ. de Jaén, 23071 Jaén, Spain
22 Dept. of Physics & Astronomy, Univ. of Hawaii, Hilo, Hawaii 96720-4091, USA
23 INAF, Osservatorio Astronomico di Roma, 00040 Monte Porzio Catone (RM), Italy
24 INAF, Osservatorio Astronomico di Collurania Teramo, 64100 Teramo, Italy
25 Osservatorio Astronomico, Univ. di Perugia, 06126 Perugia, Italy
26 Korea Astronomy Observatory, Taejeon 305-348, Korea
27 Inst. for Astrophysical Research, Boston Univ., Boston, MA 02215, USA
28 Abastumani Observatory, 383762 Abastumani, Georgia
29 Special Astrophysical Observatory, Karachaevo-Cherkessia, 369167, Russia
30 Dipartimento di Fisica, Univ. di Roma "La Sapienza", 00185 Roma, Italy
31 Michael Adrian Observatory, 65468 Trebur, Germany
32 Landessternwarte Heidelberg, Königstuhl, 69117 Heidelberg, Germany
33 Indian Inst. of Astrophysics, Bangalore 560 034, India
34 Agrupació Astronòmica de Sabadell, 08200 Sabadell, Spain
35 Dept. of Applied Physics & Instrumentation, Cork Inst. of Technology, Cork, Ireland
36 SARA Observatory, Florida International Univ., Miami, FL 33199, USA
37 Inst. of Astronomy and Astrophysics, National Observatory of Athens, 11810 Athens, Greece
A multiwavelength campaign on the BL Lac object AO 0235+16 has been organized by the WEBT collaboration during the observing seasons 2003-2004 and 2004-2005. Here we report on the results of the first season, which saw the participation of 24 optical and near-IR telescopes and 4 radio telescopes, as well as the first XMM-Newton pointing, which occurred on January 18-19, 2004. Unpublished data from previous epochs were also collected. In the optical and near-IR the source has been very active in the last 3 years, though rather faint most of the time, with noticeable variations of more than a mag in a few days. In contrast, in the radio bands it appears "quiescent" since early 2000. The X-ray spectra obtained by the three EPIC detectors are well fitted by a power law with extra-absorption at z=0.524. No significant variation of the X-ray flux occurred during the pointing. In contrast, contemporaneous dense radio monitoring with the 100 m telescope at Effelsberg shows a  2-3% flux decrease in 6-7 hours, which, if intrinsic, would imply a brightness temperature well above the Compton limit. We construct the broad-band spectral energy distribution of January 18-19, 2004 with simultaneous radio data from Effelsberg, optical data from the Nordic Optical Telescope, optical-UV data from the Optical Monitor onboard XMM-Newton, and X-ray data by the EPIC instruments. Particular care was taken to correct data for extinction due to both the Milky Way and the z=0.524 absorber. The resulting SED suggests the existence of a bump in the UV spectral region.
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On 1 Aug 2004, 17:09.