Abstract
Intraday variability in compact flat-spectrum radio sources has been intensivelystudied in recent years. For most IDV events the apparent brightness temperaturesderived from the observed timescales are in the range of T b,app ~ 1016-18 K. For extremelyrapid variations, T b,app can reach up to ~ 1021 K (e.g. Kedziora-Chudczeret al., 1997). Refractive interstellar scintillation may be the most likely extrinsicmechanism (Rickett et al., 1995; Qian, 1994a; Qian, 1994b). Especially for thecase of extreme T b,app (> 1018 K) RISS may be dominant (Dennet-Thorpe and deBruyn, 2000). However, some mv events with T app ~ 1017-18 K show evidencefor an intrinsic origin, e.g. the correlated radio-optical intraday variations observedin the BL Lac object 0716+714 (Wagner and Witzel, 1995, Qian et al., 1996).It seems important to distinguish between IDV which is a phenomenon intrinsicto the compact radio sources and IDV which is primarily due to RISS. Multifrequencypolarization and VLBI observations would be most helpful (Gabuzda andKochanev, 1997).
Published Version
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