Annual Modulation in the Intraday Variability of Quasar 0917+624 due to Interstellar Scintillation
Annual Modulation in the Intraday Variability of Quasar 0917+624 due to Interstellar Scintillation
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DOI：
10.1086/319493
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发表时间：
2001-02
期刊：
影响因子：
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通讯作者：
B. Rickett;A. Witzel;A. Kraus;T. Krichbaum;S. J. Q. M. F. Radioastronomie;Bonn;B. Observatory
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文献类型：
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作者：
B. Rickett;A. Witzel;A. Kraus;T. Krichbaum;S. J. Q. M. F. Radioastronomie;Bonn;B. Observatory
类星体0917+624是研究得最好的日内变射电源之一。然而，关于根本原因是内在的还是外在的争论仍在继续。以前的许多工作都假设日内变化（IDV）是内在的，这意味着一个非常紧凑的无线电发射源;相反，由于星际闪烁（ISS）的外在变化意味着一个相对较大的源直径，虽然在相对论性喷流模型预期的范围较小的一端。Kraus等人在1998年9月报道了在6厘米波长处IDV的显著减慢，并认为是源的变化造成的。然而，在这里，我们表明，放缓是一致的，每年调制的闪烁时标预期国际空间站，假设散射介质移动与当地标准的休息（LSR）。国际空间站的时间尺度由国际空间站的空间尺度除以地球相对于散射等离子体的速度决定。在0917+624的方向上，地球相对于LSR的横向速度变化很大，在9月至11月的几个月里有一个很深的最小值。因此，1998年9月IDV的减缓强烈表明，ISS而不是源的内在变化是IDV的主要原因。
The quasar 0917+624 has been one of the best-studied intraday variable radio sources. However, debate continues as to whether the underlying cause is intrinsic or extrinsic. Much previous work has assumed the intraday variability (IDV) to be intrinsic, which implies an extraordinarily compact source for the radio emission; in contrast, an extrinsic variation due to interstellar scintillation (ISS) implies a relatively larger source diameter, although at the smaller end of the range expected for relativistic jet models. Kraus et al. reported a marked slowing of the IDV at a wavelength of 6 cm in 1998 September and suggested that a change in the source was responsible. However, here we show that the slowing is consistent with the annual modulation in the scintillation timescale expected for ISS, under the assumption that the scattering medium moves with the local standard of rest (LSR). The ISS timescale is governed by the ISS spatial scale divided by the Earth's velocity relative to the scattering plasma. It happens that in the direction of 0917+624, the transverse velocity of the Earth with respect to the LSR varies widely, with a deep minimum in the months of September-November. Hence, the slowing of the IDV in 1998 September strongly suggests that ISS rather than intrinsic variation of the source is the dominant cause of the IDV.