Radio Sounding Measurements of the Solar Corona Using Giant Pulses of the Crab Pulsar in 2018

Observations of the Crab pulsar at 327 MHz were made at the Toyokawa Observatory of the Institute for Space-Earth Environmental Research, during the solar occultation in mid-June 2018 to investigate the coronal plasma density in the weak sunspot cycle, Cycle 24. The dispersion measurements (DMs) were determined using giant pulses detected from observations of the Crab pulsar. The systematic increase in DM over the background level, observed during the period of the closest approach of the Crab pulsar’s line-of-sight to the Sun, was ascribed to the effect of the coronal plasma. A coronal density model assuming spherical symmetry was determined by fitting it to the DM data, and was compared with those determined in past solar cycles. The best-fit model had large errors, and indicated a systematically higher value than those derived from past observations. The results obtained here are likely to be significantly affected by latitude/longitude variation in coronal plasma density, the time variation of the interstellar medium, mainly the Crab nebula, and increased measurement errors due to the reduced occurrence of giant pulses. Hence, further observations are needed to derive conclusions about a change of coronal density in the current cycle.
ファイル公開：2021/06/19