THE LOCAL INTERSTELLAR SPECTRUM BEYOND THE HELIOPAUSE: WHAT CAN BE LEARNED FROM<i>VOYAGER</i>IN THE INNER HELIOSHEATH?

Herbst, K.; Heber, B.; Kopp, A.; Sternal, O.; Steinhilber, F.

doi:10.1088/0004-637x/761/1/17

Cited by 26 publications

(17 citation statements)

References 24 publications

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“…Whether or not there should be a gradient in the LISM has been a subject of debate, with several researchers claiming there should be a positive radial gradient beyond the heliopause (Scherer et al 2011;Herbst et al 2012;Strauss et al 2013;Strauss & Potgieter 2014) and others claiming there should be no gradient at all (Jokipii 2001;Guo & Florinski 2014;Kóta & Jokipii 2014). For example, Strauss & Potgieter (2014) argue that protons with 100 MeV should increase by 25% to 40% over a Figure 11.…”

Section: Discussionmentioning

confidence: 99%

Galactic Cosmic Rays in the Local Interstellar Medium: Voyager 1 Observations and Model Results

Cummings

Stone

Heikkila

et al. 2016

ApJ

497

565

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Since 2012 August Voyager 1 has been observing the local interstellar energy spectra of Galactic cosmic-ray nuclei down to 3 MeV nuc −1 and electrons down to 2.7 MeV. The H and He spectra have the same energy dependence between 3 and 346 MeV nuc −1 , with a broad maximum in the 10-50 MeV nuc −1 range and a H/He ratio of 12.2 ± 0.9. The peak H intensity is ∼15 times that observed at 1 AU, and the observed local interstellar gradient of 3-346 MeV H is −0.009 ± 0.055% AU −1, consistent with models having no local interstellar gradient. The energy spectrum of electrons (e − + e + ) with 2.7-74 MeV is consistent with E −1.30±0.05 and exceeds the H intensity at energies below ∼50 MeV. Propagation model fits to the observed spectra indicate that the energy density of cosmic-ray nuclei with >3 MeV nuc −1 and electrons with >3 MeV is 0.83-1.02 eV cm −3 and the ionization rate of atomic H is in the range of 1.51-1.64 × 10. This rate is a factor >10 lower than the ionization rate in diffuse interstellar clouds, suggesting significant spatial inhomogeneity in low-energy cosmic rays or the presence of a suprathermal tail on the energy spectrum at much lower energies. The propagation model fits also provide improved estimates of the elemental abundances in the source of Galactic cosmic rays.

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Section: Discussionmentioning

confidence: 99%

Galactic Cosmic Rays in the Local Interstellar Medium: Voyager 1 Observations and Model Results

Cummings

Stone

Heikkila

et al. 2016

ApJ

497

565

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“…Since LIS is not measured directly, i.e., outside the heliosphere, it is not well known in the energy range affected by CR modulation (below 100 GeV). Recent data from Voyager 1 and 2 spacecraft traveling beyond the termination shock give a clue for the lower-ebergy range of LIS (Webber et al 2008;Bisschoff and Potgieter 2016), although the residual modulation beyond the heliopause may still affect this (Herbst et al 2012). Presently-used approximations for LIS (e.g., Garcia-Munoz et al 1975;Burger et al 2000;Higbie 2003, 2009) agree with each other for energies above 20 GeV but may contain uncertainties of up to a factor of 1.5 around 1 GeV.…”

Section: Heliospheric Modulation Of Cosmic Raysmentioning

confidence: 99%

A history of solar activity over millennia

Usoskin

2017

Living Rev Sol Phys

391

241

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Presented here is a review of present knowledge of the long-term behavior of solar activity on a multi-millennial timescale, as reconstructed using the indirect proxy method. The concept of solar activity is discussed along with an overview of the special indices used to quantify different aspects of variable solar activity, with special emphasis upon sunspot number. Over long timescales, quantitative information about past solar activity can only be obtained using a method based upon indirect proxies, such as the cosmogenic isotopes 14 C and 10 Be in natural stratified archives (e.g., tree rings or ice cores). We give an historical overview of the development of the proxy-based method for past solar-activity reconstruction over millennia, as well as a description of the modern state. Special attention is paid to the verification and cross-calibration of reconstructions. It is argued that this method of cosmogenic isotopes makes a solid basis for studies of solar variability in the past on a long timescale (centuries to millennia) during the Holocene. A separate section is devoted to reconstructions of strong solar energetic-particle (SEP) events in the past, that suggest that the present-day average SEP flux is broadly consistent with estimates on longer timescales, and that the occurrence of extra-strong events is unlikely. Finally, the main features of the long-term evolution of solar magnetic activity, including the

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“…Though it is believed that with measurements from Voyager 1 spacecraft in the vicinity of the heliopause [Decker et al, 2012] and highly accurate measurements by the PAMELA mission [Adriani et al, 2011], it is now possible to determine the lower limit of the very LIS for protons, helium, and other ions with numerical simulations [Herbst et al, 2012]. Nevertheless, the true LIS is still far from conclusive [Webber et al, 2013].…”

Section: Modulation Modelmentioning

confidence: 99%

Modulation of galactic cosmic rays during the unusual solar minimum between cycles 23 and 24

et al. 2014

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During the recent solar minimum between cycles 23 and 24 (solar minimum P23/24), the intensity of galactic cosmic rays (GCR) measured at the Earth was the highest ever recorded since space age. It is the purpose of this paper to resolve the most plausible mechanism for this unusually high intensity. A GCR transport model in three‐dimensional heliosphere based on a simulation of Markov stochastic process is used to find the relation of cosmic ray modulation to various transport parameters, including solar wind (SW) speed, distance of heliospheric boundary, magnitude of interplanetary magnetic field (IMF) at the Earth, tilt angle of heliospheric current sheet, and values of parallel and perpendicular diffusion coefficients. We calculate GCR proton energy spectra at the Earth for the last three solar minima P21/22, P22/23, and P23/24, with the transport parameters obtained from observations. Besides weak IMF magnitude and slow SW speed, we find that a possible low magnetic turbulence, which increases the parallel diffusion and reduces the perpendicular diffusion in the polar direction, might be an additional possible mechanism for the high GCR intensity in the solar minimum P23/24.

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THE LOCAL INTERSTELLAR SPECTRUM BEYOND THE HELIOPAUSE: WHAT CAN BE LEARNED FROMVOYAGERIN THE INNER HELIOSHEATH?

Cited by 26 publications

References 24 publications

Galactic Cosmic Rays in the Local Interstellar Medium: Voyager 1 Observations and Model Results

Galactic Cosmic Rays in the Local Interstellar Medium: Voyager 1 Observations and Model Results

A history of solar activity over millennia

Modulation of galactic cosmic rays during the unusual solar minimum between cycles 23 and 24

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