Latitudinal and radial gradients of galactic cosmic ray protons in the inner heliosphere – PAMELA and Ulysses observations N. De Simone1, V. Di Felice1, J. Gieseler3, M. Boezio2, M. Casolino1, P. Picozza1, PAMELA Collaboration†, and B. Heber3 1INFN, Structure of Rome "Tor Vergata" and Physics Department of University of Rome "Tor Vergata", Via della Ricerca Scientifica 1, I-00133 Rome, Italy 2INFN, Structure of Trieste and Physics Department of University of Trieste, I-34147 Trieste, Italy 3Inst. für Experimentelle und Angewandte Physik, Christian-Albrechts-Universität Kiel, Leibnizstr. 11, 24118 Kiel, Germany
Received: 15 Nov 2010 – Revised: 07 Mar 2011 – Accepted: 13 Apr 2011 – Published: 22 Sep 2011
Abstract. Ulysses, launched on 6 October 1990, was placed in an
elliptical, high inclined (80.2°) orbit around the Sun, and was
switched off in June 2009. It has been the only spacecraft exploring
high-latitude regions of the inner heliosphere. The Kiel Electron
Telescope (KET) aboard Ulysses measures electrons from 3 MeV to a few
GeV and protons and helium in the energy range from 6 MeV/nucleon to
above 2 GeV/nucleon. The PAMELA (Payload for Antimatter Matter
Exploration and Light-nuclei Astrophysics) space borne experiment was
launched on 15 June 2006 and is continuously collecting data
since then. The apparatus measures electrons, positrons, protons,
anti-protons and heavier nuclei from about 100 MeV to several hundreds
of GeV. Thus the combination of Ulysses and PAMELA measurements is
ideally suited to determine the spatial gradients during the extended
minimum of solar cycle 23. For protons in the rigidity interval
1.6–1.8 GV we find a radial gradient of 2.7%/AU and a latitudinal
gradient of −0.024%/degree. Although the latitudinal gradient is as
expected negative, its value is much smaller than predicted by current
particle propagation models. This result is of relevance for the study
of propagation parameters in the inner heliosphere.
Citation: De Simone, N., Di Felice, V., Gieseler, J., Boezio, M., Casolino, M., Picozza, P., PAMELA Collaboration†, and Heber, B.: Latitudinal and radial gradients of galactic cosmic ray protons in the inner heliosphere – PAMELA and Ulysses observations, Astrophys. Space Sci. Trans., 7, 425-434, doi:10.5194/astra-7-425-2011, 2011.