On the Directivity of Low-Frequency Type IV Radio Bursts

摘要

An intense type IV radio burst was observed by the STEREO Behind (STB)spacecraft located about 144 degres behind Earth. The burst was associated witha large solar eruption that occurred on the backside of the Sun (N05E151) closeto the disk center in the STB view. The eruption was also observed by theSTEREO Ahead (STA) spacecraft (located at 149 degrees ahead of Earth) as aneruption close to the west limb (N05W60) in that view. The type IV burst wascomplete in STB observations in that the envelope reached the lowest frequencyand then receded to higher frequencies. The burst was partial viewed from STA,revealing only the edge coming down to the lowest frequency. The type IV burstwas not observed at all near Earth because the source was 61 degrees behind theeast limb. The eruption was associated with a low-frequency type II burstobserved in all three views, although it was not very intense. Solar energeticparticles were also observed at both STEREOs and at SOHO, suggesting that theshock was much extended, consistent with the very high speed of the CME (about2048 km/s). These observations suggest that the type IV emission is directedalong a narrow cone above the flare site. We confirm this result statisticallyusing the type IV bursts of solar cycle 23.