Explanation of Heliospheric Energetic Neutral Atom Fluxes Observed by the Interstellar Boundary Explorer

Zirnstein, E. J.; Kim, T. K.; Dayeh, M. A.; Rankin, J. S.; McComas, D. J.; Swaczyna, P.

doi:10.3847/2041-8213/ac92e2

Cited by 7 publications

(6 citation statements)

References 54 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…However, one limitation of this model was that the heating of PUIs across the termination shock was modeled via a polytropic heating relation. The authors did find that particlein-cell and test particle simulations have indicated a polytropic heating index ranging from ∼2.0 to 2.5, which is close to the results of Zirnstein et al (2022).…”

Section: Introductionsupporting

confidence: 68%

“…testing various diffusion rates and ion distributions. Zirnstein et al (2022) indicated the importance of heating at the termination shock and acceleration of PUIs in the heliosheath, but also required an outer heliosheath population to provide agreement with IBEX-Hi observations. Our results suggest that the heating and acceleration of PUIs both at the termination shock and in the heliosheath is required to replicate ENA observations; however, a quantitative theoretical model is needed before firm conclusions can be drawn.…”

Section: Simulating the Ena Flux In The Heliosheathmentioning

confidence: 96%

“…The authors concluded that some additional heating, or acceleration, of the PUI distribution in the heliosheath was necessary to replicate the data trend for all energies, especially at energies from 4 to 10 keV. Zirnstein et al (2022) were able to quantitatively replicate the IBEX-Hi flux in the Voyager 2 direction via ENA modeling by including flux contributions from PUI heating at the termination shock, heating in the heliosheath (characterized as the region between the termination shock and heliopause), and from the outer heliosheath (characterized by the secondary ion population beyond the heliopause). They model the distribution of PUIs by assuming a generalized filled-shell distribution (McComas et al 2021) and found that PUI heating at the termination shock is important for matching observations from IBEX-Hi.…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

An Anomalous Cosmic-Ray Mediated Termination Shock: Implications for Energetic Neutral Atoms

Kornbleuth

Opher

Zank

et al. 2023

ApJL

View full text Add to dashboard Cite

The Voyager 2 crossing of the termination shock indicated that most of the upstream energy from the thermal solar wind ions was transferred to pickup ions (PUIs) and other energetic particles downstream of the shock. We use hybrid simulations at the termination shock for the Voyager 2, flank, and tail directions to evaluate the distributions of different ion species downstream of the shock over the energy range of 0.52–55 keV. Here, we extend the work of Gkioulidou et al., which showed an energy-dependent discrepancy between modeled and energetic neutral atom (ENA) observations, and fit distributions to a hybrid model to show that a population of PUIs accelerated via diffusive shock acceleration (DSA) to become low-energy anomalous cosmic rays (ACRs) can bridge the gap between modeled and observed ENA fluxes. Our results with the inclusion of DSA via hybrid fitting give entirely new and novel evidence that DSA at the termination shock is likely to be an important physical process. These ACRs carry a significant fraction of the energy density at the termination shock (22%, 13%, and 19% in the Voyager 2, flank, and tail directions, respectively). Using these ACRs in global ENA modeling of the heliosphere from 0.52 to 55 keV, we find that scaling factors as large as 1.8–2.5 are no longer required to match ENA observations at energies of ∼1–4 keV. Large discrepancies between modeled and observed ENAs only remain over energies of 4–20 keV, indicating that there may be a further acceleration mechanism in the heliosheath at these energies.

show abstract

Section: Introductionsupporting

confidence: 68%

Section: Simulating the Ena Flux In The Heliosheathmentioning

confidence: 96%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

An Anomalous Cosmic-Ray Mediated Termination Shock: Implications for Energetic Neutral Atoms

Kornbleuth

Opher

Zank

et al. 2023

ApJL

View full text Add to dashboard Cite

show abstract

“…While the enhancement at the azimuthal angle of ∼220°in 2009 is visible in both the Ribbon-separated and total flux maps, the enhancement near the azimuthal angle of ∼0°in 2019 in the total map is not visible in the separated Ribbon. The increase in 2019 is an expanding global feature in response to the increase of the SW dynamic pressure (McComas et al 2019(McComas et al , 2020Zirnstein et al 2022a). Panels (c) and (d) show that there is an overall drop in the Ribbon-only fluxes, most pronounced at lower energies with an asymmetric behavior.…”

Section: Data Methodology and Observationsmentioning

confidence: 94%

Investigating the IBEX Ribbon Structure a Solar Cycle Apart

Dayeh

Zirnstein

Swaczyna

et al. 2023

ApJ

Self Cite

View full text Add to dashboard Cite

A “Ribbon” of enhanced energetic neutral atom (ENA) emissions was discovered by the Interstellar Boundary Explorer in 2009, redefining our understanding of the heliosphere boundaries and the physical processes occurring at the interstellar interface. The Ribbon signal is intertwined with that of a globally distributed flux (GDF) that spans the entire sky. To a certain extent, Ribbon separation methods enabled examining its evolution independent of the underlying GDF. Observations over a full solar cycle revealed the Ribbon’s evolving nature, with intensity variations closely tracking those of the solar wind (SW) structure after a few years delay, accounting for the SW–ENA recycling process. In this work, we examine the Ribbon structure, namely its ENA fluxes, angular extent, width, and circularity properties for two years, 2009 and 2019, representative of the declining phases of two adjacent solar cycles. We find that, (i) the Ribbon ENA fluxes have recovered in the nose direction and south of it down to ∼25° (for energies below 1.7 keV) and not at mid and high ecliptic latitudes; (ii) the Ribbon width exhibits significant variability as a function of azimuthal angle; (iii) circularity analysis suggests that the 2019 Ribbon exhibits a statistically consistent radius with that in 2009. The Ribbon’s partial recovery is aligned with the consensus of a heliosphere with its closest point being southward of the nose region. The large variability of the Ribbon width as a function of azimuth in 2019 compared to 2009 is likely indicative of small-scale processes within the Ribbon.

show abstract

“…The plasma in the north and south polar regions of the IHS likely consists of advected fast solar wind during the solar minimum or of mixed fast and slow wind during the solar maximum (Dayeh et al 2012;Zirnstein et al 2017b;Shrestha et al 2020). The time difference between observations of the outbound solar wind and the ENAs with which they correlate ranges mostly from 2 to 6 yr, depending on ENA energy and the direction (Zirnstein et al 2017a(Zirnstein et al , 2022aReisenfeld et al 2019Reisenfeld et al , 2021.…”

Section: Introductionmentioning

confidence: 99%

Temperature of the Polar Inner Heliosheath: Connection to Solar Activity

Livadiotis

McComas

Zirnstein

2023

ApJ

Self Cite

View full text Add to dashboard Cite

We study the thermodynamics of the plasma protons in the polar regions of the inner heliosheath (IHS) and its connection with solar activity over solar cycle 24. First, we express the thermodynamic parameters of this plasma with respect to the year of energetic neutral atom (ENA) creation and perform a statistical analysis of temperatures, in order to provide a more precise characterization of the thermodynamics of IHS. Then, we perform an autocorrelation between the IHS temperature and the solar activity, using the proxies of sunspot number and fractional area of the polar coronal holes. We show that there is (i) high correlation between the time series of IHS proton temperatures and sunspot number, which is maximized for a time delay of τ ∼ 2.5 yr for both the north and south polar regions combined; (ii) high negative correlation between the temperature of the proton plasma in the north and south with the coronal hole fractional areas, where the time delay for the two poles combined is τ ∼ 2.71 ± 0.15 yr; and (iii) an asymmetry of a time-delay difference between the poles ∼0.22 yr, indicating that the southern polar ENA source region is ∼19 au closer than the northern one for a solar wind plasma protons of bulk speed of ∼400 km s−1. The findings demonstrate a connection between the IHS thermodynamics and solar activity through the solar wind, primarily manifested by the coronal holes expanding near solar minimum, which drives the expansion of fast solar wind over larger angles from high down to middle latitudes in the IHS.

show abstract

Explanation of Heliospheric Energetic Neutral Atom Fluxes Observed by the Interstellar Boundary Explorer

Cited by 7 publications

References 54 publications

An Anomalous Cosmic-Ray Mediated Termination Shock: Implications for Energetic Neutral Atoms

An Anomalous Cosmic-Ray Mediated Termination Shock: Implications for Energetic Neutral Atoms

Investigating the IBEX Ribbon Structure a Solar Cycle Apart

Temperature of the Polar Inner Heliosheath: Connection to Solar Activity

Contact Info

Product

Resources

About