出版社：SISSA, Scuola Internazionale Superiore di Studi Avanzati
摘要：For more than a decade from the late 1980s to the late 1990s, the intraday variable (IDV) quasar
0917+624 was known to be strongly variable with amplitude variations of 10-20% within 0.8 to
1.6 days. During that period it showed faster variability in the polarized flux and the polarization
angle than in total intensity. However, since 2000 the IDV of this source has almost ceased, attaining
a variability index of only less than a few percent. If interstellar scintillation was responsible
for the IDV in the past, one possible explanation for the sudden change of the variability mode
could be an intrinsic change in the morphology of the source, such as an increase in the size of the
structural components that are responsible for the scintillation. New jet components appearing at
the jet base could lead to a temporarily larger size of the scintillating component when compared
to the scattering size of the interstellar medium, causing quenched scintillation. In order to test
this scenario, VLBI observations of 0917+624 from 1999 to 2005 have been analysed. Here, we
summarize first results and discuss them in the framework of the quenched scintillation model.
