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

Abstract

There is new evidence which identifies seasonal changes of the variability time scale in intraday variable sources with refractive interstellar scintillation effects. Such a RISS-model takes the annual change of the Earth 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 canceled. In order to further investigate the applicability of the model for 0917+624, we performed an Effelsberg 6cm-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.

7 pages, 5 figures, conference proceedings of the `AGN Variability Across the Electromagnetic Spectrum' workshop held at CSIRO, Sydney, 25-29 June 2001. Accepted for publication in PASA

References in corpus (3)

• The discovery of a microarcsecond quasar: J1819+3845
• Annual modulation in IDV of quasar 0917+624 due to Interstellar Scintillation
• Intraday Variability in Northern Hemisphere Radio Sources

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• The IDV source J1128+5925, a new candidate for annual modulation?
• Serendipitous VLBI detection of rapid, large-amplitude, intraday variability in QSO 1156+295
• A seasonal cycle and an abrupt change in the variability characteristics of the intraday variable source S4 0954+65
• Spica and the annual cycle of PKS B1322-110 scintillations
• Intra-day variability observations and the VLBI structure analysis of quasar S4 0917+624
• Very Long Baseline Array observations of the Intraday Variable source J1128+592
• Interstellar Scintillation of an Extreme Scintillator: PKS B1144-379
• J1128+592: a highly variable IDV source
• IDV Observations & Study of the Quasar 0917+624