TY - JOUR
T1 - Heliosheath proton distribution in the plasma reference frame
AU - Zirnstein, E. J.
AU - Dayeh, M. A.
AU - Heerikhuisen, J.
AU - McComas, D. J.
AU - Swaczyna, P.
N1 - Funding Information:
This work was funded by the IBEX mission as a part of the NASA Explorer Program (80NSSC20K0719) and the IMAP mission as a part of NASA's Solar Terrestrial Probes (STP) mission line (80GSFC19C0027). E.J.Z. also acknowledges support from NASA grants 80NSSC18K1212 and 80NSSC20K0783. M.A.D. acknowledges support from NASA grant 80NSSC20K0783 and thanks George Livadiotis for helpful discussions related to this manuscript. Ulysses SW data and OMNI SW data were extracted from the SPDF (https:// spdf.gsfc.nasa.gov/). The work reported in this paper was partly performed at the TIGRESS high-performance computer center at Princeton University, which is jointly supported by the Princeton Institute for Computational Science and Engineering and the Princeton University Office of Information Technology's Research Computing department.
Publisher Copyright:
© 2021. The American Astronomical Society. All rights reserved.
PY - 2021/2
Y1 - 2021/2
N2 - Properties of the inner heliosheath (IHS) plasma are inferred from energetic neutral atom (ENA) observations by ~1 au spacecraft. However, the Compton-Getting effect due to the plasma velocity relative to the spacecraft is rarely taken into account, even though the plasma speed is a significant fraction of the ENA speed. In this study, we transform Interstellar Boundary Explorer (IBEX) ENA spectra to the IHS plasma frame using flow profiles from a 3D heliosphere simulation. We find that proton spectra in the plasma frame are steeper by ~30% to 5% at ~0.5 to 6 keV, respectively, compared to ENAs in the spacecraft frame. While radial plasma flows contribute most to the Compton-Getting effect, transverse flows at mid/high latitudes and the heliosphere flanks account for up to ~30% of the frame transformation for IBEX-Hi at ~0.7 keV and up to ~60% for IBEX-Lo at ~0.1 keV. We determine that the majority of IHS proton fluxes derived from IBEX-Hi measurements in 2009-2016 are statistically consistent with power-law distributions, with mean proton index ~2.1 and standard deviation ~0.4. We find significantly fewer spectral breaks in IBEX observations compared to early analyses, which we determine were a product of the "ion gun"background prevalent in ~2009-2012 before corrections made by McComas et al. in subsequent data releases. We recommend that future analyses of the IHS plasma utilizing ENA measurements take into account the Compton-Getting effect including radial and transverse flows, particularly IBEX and Interstellar Mapping and Acceleration Probe measurements below ~10 keV.
AB - Properties of the inner heliosheath (IHS) plasma are inferred from energetic neutral atom (ENA) observations by ~1 au spacecraft. However, the Compton-Getting effect due to the plasma velocity relative to the spacecraft is rarely taken into account, even though the plasma speed is a significant fraction of the ENA speed. In this study, we transform Interstellar Boundary Explorer (IBEX) ENA spectra to the IHS plasma frame using flow profiles from a 3D heliosphere simulation. We find that proton spectra in the plasma frame are steeper by ~30% to 5% at ~0.5 to 6 keV, respectively, compared to ENAs in the spacecraft frame. While radial plasma flows contribute most to the Compton-Getting effect, transverse flows at mid/high latitudes and the heliosphere flanks account for up to ~30% of the frame transformation for IBEX-Hi at ~0.7 keV and up to ~60% for IBEX-Lo at ~0.1 keV. We determine that the majority of IHS proton fluxes derived from IBEX-Hi measurements in 2009-2016 are statistically consistent with power-law distributions, with mean proton index ~2.1 and standard deviation ~0.4. We find significantly fewer spectral breaks in IBEX observations compared to early analyses, which we determine were a product of the "ion gun"background prevalent in ~2009-2012 before corrections made by McComas et al. in subsequent data releases. We recommend that future analyses of the IHS plasma utilizing ENA measurements take into account the Compton-Getting effect including radial and transverse flows, particularly IBEX and Interstellar Mapping and Acceleration Probe measurements below ~10 keV.
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U2 - 10.3847/1538-4365/abd092
DO - 10.3847/1538-4365/abd092
M3 - Article
AN - SCOPUS:85101624895
VL - 252
JO - Astrophysical Journal, Supplement Series
JF - Astrophysical Journal, Supplement Series
SN - 0067-0049
IS - 2
M1 - abd092
ER -