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Annual Modulation in the Variability Properties of the IDV Source 0917+624?

Published online by Cambridge University Press:  05 March 2013

L. Fuhrmann ,
T. P. Krichbaum ,
G. Cimò ,
T. Beckert ,
A. Kraus ,
A. Witzel ,
J. A. Zensus ,
S. J. Qian  and
B. J. Rickett
L. Fuhrmann
Affiliation:
Max-Planck-Institut für Radioastronomie, Bonn
T. P. Krichbaum
Affiliation:
Max-Planck-Institut für Radioastronomie, Bonn
G. Cimò
Affiliation:
Max-Planck-Institut für Radioastronomie, Bonn
T. Beckert
Affiliation:
Max-Planck-Institut für Radioastronomie, Bonn
A. Kraus
Affiliation:
Max-Planck-Institut für Radioastronomie, Bonn
A. Witzel
Affiliation:
Max-Planck-Institut für Radioastronomie, Bonn
J. A. Zensus
Affiliation:
Max-Planck-Institut für Radioastronomie, Bonn
S. J. Qian
Affiliation:
Max-Planck-Institut für Radioastronomie, Bonn Beijing Astronomical Observatory, China
B. J. Rickett
Affiliation:
University of California, San Diego
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Abstract

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There is new evidence which identifies seasonal changes of the variability time scale in intraday variable (IDV) sources with refractive interstellar scintillation effects. Such a RISS model takes the annual change of the Earth's velocity relative to the scattering medium into account. In September 1998 we found a remarkable prolongation of the variability time scale in the IDV source 0917+624 with only small variations in flux density during a period of 5 days. This was explained as a seasonal effect, in which the velocity vector of the Earth and the interstellar medium nearly cancelled. In order to further investigate the applicability of the model for 0917+624, we performed an Effelsberg 6 cm-flux monitoring program over the course of one year. Since September 2000, the source appears to be remarkably inactive and yet (May 2001) no return to its normal, faster and stronger variability pattern is observed. Here, our observational results and a possible explanation for the current quiescence are presented.

Keywords

quasars: individual (0917+62)radio continuum: ISMscattering
Type
Research Article
Information
Publications of the Astronomical Society of Australia , Volume 19 , Issue 1 , 2002 , pp. 64 - 68
Copyright
Copyright © Astronomical Society of Australia 2002

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