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Ground-Based Observations of PKS2155-304 in November 1991

Published online by Cambridge University Press:  19 July 2016

A. Blecha ,
T. J.-L Courvoisier ,
H. D. Aller ,
M. F. Aller ,
P. Bouchet ,
P. Bratschi ,
M. T. Carini ,
M. Donahue ,
E. D. Feigelson  and
A. V. Filippenko
...Show all authors
A. Blecha
Affiliation:
1Geneva Observatory, CH–1290 Sauverny, Switzerland
T. J.-L Courvoisier
Affiliation:
1Geneva Observatory, CH–1290 Sauverny, Switzerland
H. D. Aller
Affiliation:
2Astronomy Department, University of Michigan, Ann Arbor, Michigan 48109–1090, US
M. F. Aller
Affiliation:
2Astronomy Department, University of Michigan, Ann Arbor, Michigan 48109–1090, US
P. Bouchet
Affiliation:
3European Southern Observatory, Casilla 19001, Santiago 19, Chil
P. Bratschi
Affiliation:
1Geneva Observatory, CH–1290 Sauverny, Switzerland
M. T. Carini
Affiliation:
4Computer Sciences Corporation, NASA/GSFC, Greenbelt, MD 20771, US
M. Donahue
Affiliation:
5Carnegie Observatories, 813 Santa Barbara St., Pasadena, CA 91101, US
E. D. Feigelson
Affiliation:
6Department of Astronomy and Astrophysics, 525 Davey Lab, Pennsylvania State University, University Park, PA 16802, USA
A. V. Filippenko
Affiliation:
7Department of Astronomy, University of California, Berkeley, CA 94720, USA
I. S. Glass
Affiliation:
8South Africa Astronomical Observatory, PO Box 9, Observatory 7935, South Africa
J. Heidt
Affiliation:
9Landessternwarte Heidelberg-Königstuhl, Königstuhl, D-69117 Heidelberg, Germany
P. A. Hughes
Affiliation:
2Astronomy Department, University of Michigan, Ann Arbor, Michigan 48109–1090, US
R. I. Kollgaard
Affiliation:
6Department of Astronomy and Astrophysics, 525 Davey Lab, Pennsylvania State University, University Park, PA 16802, USA
T. Matheson
Affiliation:
7Department of Astronomy, University of California, Berkeley, CA 94720, USA
H. R. Miller
Affiliation:
10Department of Physics, Georgia State University, Atlanta, GA 30303
J. C. Noble
Affiliation:
10Department of Physics, Georgia State University, Atlanta, GA 30303
P. S. Smith
Affiliation:
11Steward Observatory, University of Arizona, Tucson, AZ 85721, USA
S. Wagner
Affiliation:
9Landessternwarte Heidelberg-Königstuhl, Königstuhl, D-69117 Heidelberg, Germany

Abstract

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We present ground-based data of the BL Lac object PKS 2155-305 obtained during a large international campaign spanning the electro–magnetic spectrum from the radio waves to X-rays in November 1991. For the complete description of the observations and data analysis we refer to the paper by Courvoisier et al. 1993, and references therein. The ground-based data include radio, infrared JHKL and UBVRI fluxes as well as optical and near IR polarimetry.

The broad-band optical and near IR data from U to I exhibit the same behaviour in all bands: the flux nearly doubled over the well-covered period of 23 days. The cross-correlation function does not reveal any significant changes in the light-curves. Though significant variations in 24 hours have been recorded, the cumulated Fourier power spectrum drops to the noise level for periods shorter than 2.5 days. The spectral index remained constant.

The polarised flux varied by a larger factor than the total flux and did not follow the same pattern. The degree of polarisation and polarisation angle are nearly independent of the wavelength and are strongly correlated in all filters.

In the radio domain the spectral index increased from −0.1 on November 5 to +0.02 on 25-th.

The absence of the lag between the optical and infrared bands and the polarisation variations are consistent with a model in which the variability is caused by micro-lensing of the source (Stickel, Fried and Kühr 1988). One would, however, expect in this model that the variation in the polarisation and the total flux are tightly correlated contrary to what is observed.

The constant shape of the continuum spectral energy suggests that only the number of electrons whose emission is beamed towards the observer changes, rather than the arrival of fresh electrons that are being accelerated.

The variability of the polarisation may be explained by changes in the geometry of the magnetic field (dominant direction). This is consistent with the observed variations of the polarisation angle.

Type
Poster Contributions: Continuum studies
Information
Symposium - International Astronomical Union , Volume 159: Multi-Wavelength Continuum Emission of AGN , 1994 , pp. 319
Copyright
Copyright © Kluwer 1994 

References

Courvoisier, T. J.-L. et al. 1993 Ap. J. submitted Google Scholar
Stickel, M., Fried, J.W. and Kühr, H., 1988, A&A 191, L16 Google Scholar