35th International Cosmic Ray Conference The Anisotropy of Anomalous Cosmic Rays Observed by Voyager 2 in the Heliosheath A. C. Cummings and E. C. Stone, Caltech N. Lal and B. Heikkila, Goddard Space Flight Center W. R. Webber, New Mexico State University 35th International Cosmic Ray Conference Busan, Korea 14 July 2017

TSP TSP ACR TSP ACR ACR GCR GCR GCR Counter to expectations, higher energy ACRs not accelerated at shock in heliospheric nose region TSP spectrum normalized at low energies to estimate TSP contributions at higher energies Thanks to LECP team for low-E Ions, He, and O data

McComas & Schwadron 2006 McComas and Schwadron pointed out that near the nose of the heliosphere where V1 and V2 crossed the termination shock, the field lines threading through the Voyagers aren’t in contact with the TS locally long enough to accelerate particles to the higher energies of the ACRs. Longer connection times occur further back along flank of termination shock, so higher energies would have diffusive flow toward nose A diffusive flow toward the nose creates a diffusive anisotropy A convective flow toward the flank creates a CG anisotropy

Kota 30th ICRC 2007

Factor of 10 gradient between nose and tail (~300AU) Kota & Jokipii AIP CP 1039 2008

Will use V2 “magrol” data to investigate anisotropy of ACRs – indirectly by determining components of solar wind velocity vector via the Compton-Getting effect and comparing with V2 plasma instrument results.

The Compton-Getting Effect for Determining Solar Wind Velocity Pioneered by LECP team (Decker, Krimigis, et al.) – led to discovery of stagnation region that V1 went through prior to crossing the heliopause. CRS contributed estimate of N component, which trended towards zero in the stagnation region. If a particle distribution is isotropic in the frame of the solar wind, it will be anisotropic in the frame of the spacecraft. Based on Forman, 1970: δ= <(𝟐−𝟐γ)/𝒗)>𝑽 where dJ/dE = AEγ , v = particle velocity, and V = solar wind velocity. Thus can calculate V from measurement of observed anisotropy magnitude and can get direction from location of minimum intensity. With CRS instrument, measured energy spectra and simulations are used to calculate <(𝟐−𝟐γ)/𝒗)> for periods of interest. Roughly, for recent periods at V2, including a +20% correction due to telescope opening angle of 120o : V (km/s) ~ 3800* δ

N -R T “”magrols” = 10 revolutions about R axis CCW as viewed from Sun. 2000 seconds per revolution. N Intensity of low energy ions measured every 48 sec on CRS. -R T

CRS instrument on Voyager 1 D B A 11.25 inches

Roll modulations are observed. So, there is an anisotropy.

When binned by angle from N axis towards T axis, the minimum represents the direction of flow in the N-T plane. Roll 64: N-T angle = 152.1o +- 5.2o Roll 66: N-T angle = 100.9o +- 4.2o So we see large variations in N-T angle. We also see variations in the anisotropy amplitude as well. Roll 64 LET A LET C LET D Roll 66 LET A LET C LET D

VR (top panel) not measured by CRS, but VT and VN determinations are very insensitive to VR. (Can vary VR by x2 and VN and VT determinations change by <0.3%) CRS VT are below PLS VT by up to ~80 km/s. (Two points near ~200 km/s are large non-convective flows.) CRS VN is in fair agreement with PLS

From Richardson & Decker, ApJ, 2014. (red = PLS; black = LECP) VT from LECP 28-43 keV protons are generally in good agreement with PLS, whereas VT from CRS at 0.5-35 MeV/nuc is not. Conclusion: V2 CRS is often seeing a diffusive flow in the direction of –T at 0.5-35 MeV, which counteracts the convective flow of the solar wind to some extent. This diffusive flow is typically not seen by LECP at 28-43 keV. This suggests that 0.5-35 MeV protons are coming from flank of termination shock and 28-43 keV protons are being convected with the solar wind from the nose of the termination shock.

40 keV 6 MeV Kóta ICRC 2007 +R +T V2 V2 Direction of diffusive flow of ACRs is in accordance with gradient in this model. Supports picture of ACR acceleration and transport of McComas and Schwadron, 2006, Kóta and Jokipii, 2006, and Kóta, 2007. Figures from Kóta 2007 shown: acceleration of low-energy particles is fast and local – more uniform distribution. Acceleration inefficient at nose – particles diffuse towards nose from flank or tail (in –T direction). A source in the +T direction was also suggested by Stone & Cummings, 2011, in analysis of V1 magrol data.

ACR H at V2 with 0.5-35 MeV appears to observe a source in the +T direction, suggesting ACRs in the heliosheath maybe be approaching from flank or tail of termination shock. V1 data suggested the same (Stone & Cummings, 32nd ICRC, 2011) Supports picture of McComas and Schwadron, 2006, Kóta and Jokipii, 2006, and Kóta, 2007. Summary