Erratum: ``Identification of a Peculiar Radio Source in the Aftermath of Large Coronal Mass Ejection Events'' (ApJ, 656, L105 [2007])

Details Erratum: ``Identification of a Peculiar Radio Source in the Aftermath of Large Coronal Mass Ejection Events'' (ApJ, 656, L105 [2007]) Erratum: ``Identification of a Peculiar Radio Source in the Aftermath of Large Coronal Mass Ejection Events'' (ApJ, 656, L105 [2007])

Aug 2007

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007apj...665l.179v&link_type=abstract

The Astrophysical Journal, Volume 665, Issue 2, pp. L179-L179.

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Scientific paper

In our recent Letter (A. Vourlidas et al. [ApJ, 656, L105 [2007]], hereafter Paper I), we determined the azimuth and elevation of our radio source with a direction-finding algorithm (Paper I, Fig. 4) assuming that the source emission dominates over the galactic background. This is generally true for type III emissions that are mainly used for these analyses. However, this condition does not necessarily hold for weaker emissions such as the broadband continuum source in our Letter. As the source intensity decreases to near the Galactic background level, the source direction shifts toward the direction of the Galactic center. It is therefore important to subtract the background before deriving source directions, which we did not do in Paper I. This correction has now been applied to the WIND WAVES data reported in Figure 4 of Paper I. As a result, there is no more significant drift in the source elevation or azimuth. The radio continuum source remains along the ecliptic plane as do other radio bursts observed in association with this coronal mass ejection (CME) event.
This correction does not significantly alter our proposed scenarios for the origin of the broadband source. The emission could still arise from electrons injected in nearby structures originating from interactions between the expanding CME and closed coronal loops or from the closing down of previously opened loops. Our velocity estimations are also unaffected by the corrections on the source location. They still suggest that the continuum propagates too slowly to be the CME shock. However, we must point out that M. J. Reiner, M. L. Kaiser, & J.-L. Bougeret (ApJ, 656, L105 [2007]) modeled this event as a type II source deriving an initial speed of 3000 km s-1, a strong deceleration of 41 ms-2 lasting for about 15 hr, followed by an almost constant propagation to the Earth. As the authors acknowledge in their paper, these parameters were obtained using a simple generic speed profile. Currently, there are no independent observations or theoretical predictions that show such a velocity profile for interplanetary CMEs. On the other hand, patchy, drifting structures that are typical signatures of interplanetary type II bursts are clearly seen in the radio spectrum after 14:30 UT but at a higher frequency than that of our continuum source. Similar patchy emissions are seen until a shock signature at Earth on September 24 at 21:00 UT. So a type II source is present in the spectrum.
Our initial intention with this work was to bring attention to the possibility that the conventional interpretation, as type II emission from a CME-driven shock, for low-frequency drifting continua might not hold true for all cases. We suggested in Paper I that the emission mechanism of this continuum could be gyrosynchrotron from nonthermal electrons. Recently, T. S. Bastian (ApJ, 665, 805 [2007]) proposed incoherent synchrotron emission from electrons entrained in the CME as an alternative explanation for such smooth type II-like sources. Therefore, we may be confronted with a new phenomenon, and we clearly need more studies to pin down the physical mechanism.
We are grateful to M. Reiner for pointing out the need for correction of our direction-finding results and for providing a preprint of M. J. Reiner, M. L. Kaiser, & J.-L. Bougeret (ApJ, 656, L105 [2007]).

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