Speaker
UGO GIACCARI
(INFN Napoli)
Description
Recent observations from PAMELA show that the cosmic ray proton spectrum does not follow a single power law model in the rigidity range between 1 GV to 1.2 TV. The spectrum gradually softens from 30 GV up to 230 GV but around ~240 GV the spectrum becomes harder. This observed behavior is in contradiction with the predictions of a shock diffusion acceleration model and diffusive acceleration in the galaxy.
Possible explanations rely on an indication of a different population of proton sources. Anisotropy studies can help to understand better the nature of the proton spectrum. The large Larmor radius at GV rigidity range make impossible to point back to proton sources but some large scale structures, reflecting the clustering of the sources, could be still present in the proton flux.
In this contribution we will study the proton arrival direction distribution with Pamela data. Large scale structures in the distribution of cosmic ray protons could be also caused by several different effects. The heliospheric magnetic field, which configuration is not well known, may be the responsible. The general large-scale structure of the heliomagnetic field may induce structures in primary cosmic rays flux as a function of the equatorial coordinates (sidereal anisotropy).
Magnetic fields in the neighborhood of the solar system are also influenced by the solar activity and reverse their polarity at each maximum of the activity. Additional cosmic-ray intensity variations may depend on the arrival direction with respect to the Sun. Also these effects will be discussed in this contribution.
Primary author
UGO GIACCARI
(INFN Napoli)
