Enhanced Radio Source Scintillation due to Comet Austin (1989c1)

Abstract

Enhanced scintillations in the direction of the quasar 2204+29 (3C441) were observed on 13 May 1990 when the tail of Comet Austin passed in front of it. Comparison with previous observations at 103, 327 and 408 MHz of Comet Halley and at 408 MHz of Comet Wilson show that proper occultation geometry is essential for observing enhanced scintillations. It has been shown that the solar elongation € during such observations should be large, typically greater than 60· and in no case less than 30· at 103 MHz. At the time of the occultation the scintillation index (r.m.s./mean source flux) was greater than that expected for this source by a factor of 3. The r.m.s. electron density variation /IN, at a distance of 0·9 A.U. from the sun and 7·3· downstream of the nucleus, was found to be 6 cm-3 as compared with 1 cm-3 for the normal solar wind at 1 A.U. The corresponding scale sizes of the turbulence were found to be much finer than normally found in interplanetary scintillation (IPS) caused by the solar wind.

A Study of Density Modulation Index in the Inner Heliospheric Solar Wind During Solar Cycle 23

“…The IPS phenomenon therefore has a built in filter that makes it insensitive to contributions from large-scale size density irregularities. In fact, this property of IPS has even been exploited to study the fine-scale structure in cometary ion tails during radio source occultations by cometary tail plasma (Ananthakrishnan et al 1975;Janardhan et al 1991Janardhan et al , 1992.…”

Possible contribution of a solar transient to enhanced scintillation of a quasar

“…This is within the scatter at 90" as seen from Figure 1. The observed effects between the 16 and 21 December (Alurkar et al, 1986;Janardhan et al, 1992) were thus caused mainly due to the plasma tail of the comet sweeping across the line of sight in front of the source during the observations. Even if the value of AN was taken to be 0.8 cme3, ( re p resenting a 4% modulation of the mean ion density which is the case in the quiet solar wind at 0.1 AU) the expected scintillation would turn out to be 0.23 corresponding to an enhancement of around 22% over the expected value.…”

“…Period = 2082 , , , ! 700-II I ,I I I II 1 I I IIll I I I I \ I I II I II I I I I I I I I I I I I I I I II I In the earlier work (Alurkar et al, 1986;Janardhan et al, 1992), a quantitative estimate of the electron content in the plasma tail of the comet was calculated by using the equations of the thin screen theory (Salpeter, 1967)…”

“…The most recent observation is that of comet Austin (Janardhan et al, 1991). However, it is known (Houminer and Hewish, 1972;Houminer, 1973Houminer, , 1976) that large day-to-day variations in scintillation index at solar elongations greater than 60" are strongly correlated with plasma density fluctuations contained in corotating streams.…”

From the Solar Corona to Clusters of Galaxies: The Radio Astronomy of Bruce Slee

“…After these findings for Comets Wilson and Austin, Janardhan, Alurkar, Bobra, Slee and Waldron (1992) carried out an analysis of the quasar 2314+038 (3C459) that was occulted by the plasma tail of Comet 1P/Halley in 1985 December. Once again enhanced scintillations were present (see Fig.…”