**1. Introduction**

Voyager 1 has now been beyond the heliopause for over 5 years since its seminal crossing of this boundary in August of 2012. During its epic 40 year journey of ~122 AU out to this boundary and beyond this spacecraft has passed through several regions of the heliosphere including the heliosheath of extent ~30 AU just inside the heliopause (HP) where extremely large and variable intensities of protons, helium and oxygen nuclei as well as electrons between 1 and 100 MeV were observed. See earlier article in Astrophysics [1] showing and discussing these intensity time profiles.

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Then, suddenly these particles completely vanished and new and completely different spectra of particles between 1 MeV up to ~1 GeV, instantly recognizable as those for galactic cosmic rays, were observed. These LIS intensities at all energies have remained constant to within ±1% for 5 years corresponding to 20 AU beyond the HP. These low energy galactic spectra and their relation to higher energy measurements such as those made by AMS-2 will be discussed in this paper in terms of the acceleration, source distribution and propagation of cosmic rays in the galaxy.

between 3.0 and 4.0 MeV, from the time of launch (1977) to the present time (2018). These energy responses are determined by extensive GEANT-4 calculations. These telescopes are described in [2, 3]. The two intensities are normalized to those observed in local interstellar space (LIS).

Galactic Cosmic Rays from 1 MeV to 1 GeV as Measured by Voyager beyond the Heliopause

http://dx.doi.org/10.5772/intechopen.75877

63

One can define from **Figure 1** four temporal or spatial regions that apply to all the components and energies discussed here. The 1st region is from launch in 1977 to 1983.0 when V1 was at about 20AU and also near its maximum latitude of +30°. This region (nearest the Sun) is punctuated by many abrupt increases related to interplanetary propagating electron events of energy <1 MeV of solar origin. These are closely coordinated with observations inside the Earth's orbit from HELIOS during the 1977–1978 time period. The individual events are separated temporally at Voyager and HELIOS. Also included is the Jupiter encounter occurring at ~1979.2.

The second region (time period) is from 1983.0 to 2005.0 at which time V1 crossed the HTS and entered the heliosheath at ~95.0 AU and at +30°. The effects of the solar 11 year modulation cycle are rather weakly seen in this region. These variations are similar temporally to what was observed for higher energy protons [4] and shown later in **Figure 3**. Two massive solar induced interplanetary electron events are seen in the A stop rate in 1989 and 1991 when V1 was at between 40 and 50 AU. These events are related to large shocks moving outward in

During the time V1 is in the heliosheath region from 2005.0 to 2012.65 between 95 and 121.7AU (Region 3) there is a factor of 3–4 increase in the sub-MeV electron intensities which, during most of this time period, have even higher intensities than those observed beyond the HP, in the local interstellar medium. These are electrons accelerated in the heliosheath. Meanwhile the intensity of the 4 MeV electrons increases in the heliosheath from the HTS crossing to the HP by a factor ~30. This is believed to be a result of modulation effects in the heliosheath which

Beyond the heliopause (HP) in LIS the electron intensities have remained constant to within ±1% at both energies for 5 years (~18 AU of outward travel for V1). Notice that the intensities of these electrons in LIS are higher than those at the Earth by a factor ~4 at 0.7 MeV and by a factor ~20 at 4 MeV. These differences are due in part to solar modulation effects and in part

In **Figure 2** we show the 1.8–2.6 MeV proton intensity, again normalized to the LIS value that is measured for 0.7 MeV electrons. This is the lowest energy part of the interstellar proton spectrum that can be measured on Voyager in a 2-D, dE/dx, telescope mode. It represents a limit to the characteristics of the lower energy proton propagation in the galaxy from the nearest sources in the galaxy since it corresponds to only ~35μ of equivalent Si traversed during

In region 1, between launch and 1983 and inside ~20 AU, the Earth and the inner heliosphere are bathed in an almost continuous flux of 2 MeV protons which exceeds the possible background galactic cosmic rays at this energy and location by a factor ~1000 and is comparable to the intensities observed further out in the heliosheath. This continuously high intensity results from the 1.8 to 2.6 MeV protons from many individual solar events, with the intensities

the heliosphere with speeds close to 1000 km/s.

reduce the LIS intensity of these higher energy electrons.

to the local acceleration of 0.7 MeV electrons.

piling up due to the large longitudinal diffusion.

the galactic propagation.

We begin in this paper by discussing the radial intensity profiles outward from the Earth through the heliosphere and beyond into interstellar space. We will compare these intensity profiles for electrons and protons, from the lowest energies, ~1 MeV, to the higher energies of a few hundred MeV which are normally considered as cosmic rays. The profiles provide a graphic view of the scale of the various regions of the heliosphere and the entrance into the uncharted regions of interstellar space and the realm of galactic cosmic rays.

We will then discuss the spectra of galactic cosmic ray electrons, protons, helium and heavier nuclei that are measured for the 1st time by Voyager. Every step in this process provides a new insight into the features of these galactic cosmic rays that could never be studied previously because of our location within the heliosphere.
