RESIDUAL MODULATION OF GALACTIC COSMIC RAYS IN THE HELIOSPHERE

V.G. Yanke, A. V. Belov, R. T. Gushchina, P.G. Kobelev, L.A. Trefilova, The Pushkov Institute of Terrestrial Magnetism, Ionosphere and Radiowave Propagation of the Russian Academy of Sciences (IZMIRAN), Moscow, Troitsk, Russia

Precise measurements of the galactic cosmic rays (CR) spectra in Earth’s orbit using the PAMELA and AMS-02 space experiments and measurements of the interstellar spectrum at the heliospheric boundary with the help of Voyager 1 and 2 have become a powerful stimulus for a detailed study of CR modulation. The paper raises the question of how the measured intensity at the minimum of solar activity differs from the true value of the intensity of the local interstellar spectrum (LIS) of CR, and what is the residual modulation and its spectrum. Numerically, the residual modulation is defined as the variation of the intensity measured in the Earth’s orbit relative to the intensity of the interstellar spectrum. Only models involving Voyager measurements for R < 1 GV and AMS-02 for R > 100 GV were used as LIS spectra. For measurements in the Earth’s orbit, the data from a network of neutron monitors (Reff = 10 GV), from muon telescopes, and from stratospheric sounding detectors, which were calibrated by PAMELA’s data, were used.

For particles with a rigidity of 10 GV relative to the period of 2009, the value of the residual modulation is = 19 ± 0.4(stat) ± 2(sys) %, which is in good agreement with McCracken et.al., 2007. This work was based on combined data from the Climax neutron monitor and cosmogenic data. According to these data, a residual modulation value of 18 % can be obtained for the modern era. One can ask a question about the inertia of the heliosphere, i.e. about how long it will take to the cosmic rays of the interstellar spectrum to fill the entire heliosphere after solar activity reaches its minimum values. According to McCracken et.al., 2007, the intensity of cosmic rays reached the LIS level only ~50 years after, for example, the onset of the Maunder minimum. An analysis of CR modulation in the heliosphere showed that even during the quietest period of the Sun, the residual modulation is significant. It follows from this that the Sun in its active phase is capable of modulating CR relative to the quiet period in approximately the same way as the quiet Sun is capable of modulating the local interstellar spectrum.

The work was carried out using the equipment of the USU https://ckp-rf.ru/catalog/usu/433536/ “Net SKL” and was based on data from the World Network of Neutron Monitors https://www.nmdb.eu/.

Oral