Physics
Scientific paper
Dec 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011agufmsh11a1913j&link_type=abstract
American Geophysical Union, Fall Meeting 2011, abstract #SH11A-1913
Physics
[2114] Interplanetary Physics / Energetic Particles, [2124] Interplanetary Physics / Heliopause And Solar Wind Termination
Scientific paper
The source location of the anomalous cosmic rays (ACR) remains an item of debate. Energetic-particle observations from the Voyagers near and beyond the heliospheric termination shock showed that the expectations of the generally accepted, simple, models of acceleration of the ACR at the termination shock were not met. Instead, the intensities of the lowest-energy particles observed by LECP increased right at the shock, as expected whereas, at higher energies, the increase was gradual. This anomaly led to the proposal of number of alternate mechanisms, where the acceleration did not occur at the shock, but instead was due to either compressions or reconnection in the heliosheath. These alternate mechanisms have the acceleration occuring in the distant heliosheath, near the heliopause. In this talk, we point out that observations from Voyager 1 made nearly 20 years ago, when it was at some 46 AU from the Sun, well-inside of the termination shock, provide an important constraint on the distance to the source of the ACR (McDonald, et al, 2000). These authors compared the recovery of both ACR and galactic cosmic rays (GCR) from a sudden decrease caused by a merged interaction region crossing the spacecraft. The recovery of the GCR takes much longer than that of the ACR. McDonald etal used the observations to locate the source of the ACR (which at that time they identified with the termination shock) at 88.5 +/- 7 AU from the Sun. The modulation boundary for GCR was much further out. Subsequently, Kota and Jokipii (2001) modeled the effects of a GMIR, using a propagating disturbance and acceleration of the ACR by the termination shock at 90 AU. This showed good agreement with the observations. Interpreted in the light of present issues, these analyses provide a significant constraint on the radius of the source of cosmic rays, regardless of the acceleration mechanism. If the boundary of GCR modulation is at some 130 AU or further out (possibly the heliopause), then the source of ACR is significantly closer. Given the McDonald, etal estimate of 88.5 AU, the location of this source is consistent with the source being the termination shock, but not near the heliopause. Reference McDonald, F. B. etal, JGR, 105,1, 2000. Reference Jokipii, J. R. and Kota, J., Proceedings of ICRC, Hamburg, 2001.
Jokipii Randy J.
Kota József
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