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Solar modulation of cosmic ray positrons in a quiet heliosphere

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Presentation on theme: "Solar modulation of cosmic ray positrons in a quiet heliosphere"— Presentation transcript:

1 Solar modulation of cosmic ray positrons in a quiet heliosphere
Marius Potgieter Etienne Vos, Driaan Bisschoff, Jan-Louis Raath Centre for Space Research, North-West University Potchefstroom, South Africa Mirko Boezio, Riccardo Munini INFN, Trieste, Italy Valeria Di Felice INFN, Sezione di Rome “Tor Vergata”, Rome, Italy. Also: Agenzia Spaziale Italiana (ASI) Science Data Center, Frascati, Italy Research in South Africa is partially supported by the National Research Foundation (NRF) Students’ bursaries are provided by the NRF and the SA National Space Agency (SANSA) ICRC 2017

2 Transport equation for the transport, modulation and
acceleration of cosmic rays in the heliosphere Time-dependent, pitch-angle-averaged distribution function Diffusion Convection with solar wind Particle Drifts Adiabatic energy changes Any local source  Momentum diffusion in heliosheath Second order Fermi acceleration Parker (Planet. Space Science, 13, 9, 1965)

3 Conceptual illustration of modulation processes
Drift direction of electrons in A > 0 cycle Drift direction of electrons in A < 0 cycle

4 Modulation of Galactic Cosmic Rays Observed at the Earth
with two solar activity proxies Cosmic rays at sea-level Hermanus Monthly averaged sunspot numbers HCS tilt angles Wilcox Solar Observatory

5 Modeling of drift effects during a very quiet solar minimum
Prediction for next A > 0 solar minimum cycle Potgieter & Vos, A&A, 2016

6 Global modulation of cosmic ray protons: mid-2006 to end of 2009
PAMELA proton observations at the Earth PAMELA-SA bilateral cooperation: Mirko Boezio & colleagues Proton spectra published Adriani et al. ApJ 2013 Potgieter et al. Solar Phys 2014 PhD’s: Valeria Di Felice, Nico De Simone, Valerio Formato, Riccardo Munini, Etienne Vos.

7 Unexpected highest every recorded proton spectrum in 2009
Red data points: A < 0 cycles Blue data points: A > 0 cycles Strauss R.D., Potgieter M.S. Is the highest cosmic rays yet to come? Solar Physics, 289, 2014

8 PAMELA Solar Minimum Observations and Modeling
LIS Etienne Vos’ PhD

9 PAMELA Observations and Charge-sign Dependence
Protons Electrons New evidence of charge-sign-dependent (drift) modulation for from PAMELA…! But, much smaller than anticipated from modelling of previous solar minimum activity periods….! The 2009 minimum was different… Di Felice et al. ApJ., 2017 Protons Electrons

10 Modulation of positrons: mid-2006 to end of 2009
Made possible by continous high precision observations mid-2006 to end of 2009

11 Difference between electron and positron spectra for 2009
Numerical modeling with particle drifts LIS 2009 Electrons Positrons Spectra at Earth Preliminary; see PhDs of Riccardo Munini (2016) and Etienne Vos (2016)

12 Modulation factor for electrons
and positrons

13 Electron to positron ratios over time (2006-2009) and
as a function of rigidity

14 Difference between spectra for protons, electrons and positrons
At the Earth for solar minimum conditions

15 Solar wind velocity profiles in the heliosphere
Thank you !

16 The schematic heliosphere
Owens and Forsyth. Living Rev. 2013

17 Proton modulation during the unusual 2009 minimum period
Potgieter, Vos, Boezio et al. Sol Phys, 2014 Vos & Potgieter, ApJ, 2015

18 Diffusion Theory: Difference between protons and electrons
At the Earth Potgieter et al. 2013 Potgieter et al. 2015

19 Computed modulation of galactic electrons and positrons
at solar minimum for two polarity cycles Electrons Positrons Langner & Potgieter, Solar wind termination shock and heliosheath effects on charge-sign dependent modulation for protons and anti-protons, JGR, 109, 2004; Potgieter & Langner, Heliospheric modulation of cosmic ray positrons and electrons: Effects of the heliosheath and solar wind termination shock, ApJ, 602, 2004.

20 The Heliopause Spectra: Observations (V1, PAMELA, AMS02)
and GALPROP computations V1: Giant leap forward…. GALPROP: Plain diffusion; then with re-acceleration Bisschoff & Potgieter, Astrophys&SS, 2015 Protons: Vos & Potgieter, ApJ, 2015

21 The Heliopause Spectra: Observations (V1, PAMELA, AMS02) and
GALPROP computations Galactic Protons and Electrons And Positrons… Potgieter & Vos , A&A, 2016 Etienne Vos, PhD, 2015

22 Gradient, curvature and current sheet drifts:
Basic concept

23 The conceptual and simulated HCS (wavy current sheet)
Kota, 2010

24 Comparison of modulation with a LIS vs. HPS

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