Local Interstellar Magnetic Field Determined From the Interstellar Boundary Explorer Ribbon

Abstract

The solar wind emanating from the Sun interacts with the local interstellar medium (LISM), forming the heliosphere. Hydrogen energetic neutral atoms (ENAs) produced by the solar-interstellar interaction carry important information about plasma properties from the boundaries of the heliosphere, and are currently being measured by NASA's Interstellar Boundary Explorer (IBEX). IBEX observations show the existence of a “ribbon” of intense ENA emission projecting a circle on the celestial sphere that is centered near the local interstellar magnetic field (ISMF) vector. Here we show that the source of the IBEX ribbon as a function of ENA energy outside the heliosphere, uniquely coupled to the draping of the ISMF around the heliopause, can be used to precisely determine the magnitude (2.93 ± 0.08 μG) and direction (227.°28 ± 0.°69, 34.°62 ± 0.°45 in ecliptic longitude and latitude) of the pristine ISMF far (∼1000 AU) from the Sun. We find that the ISMF vector is offset from the ribbon center by ∼8.°3 toward the direction of motion of the heliosphere through the LISM, and their vectors form a plane that is consistent with the direction of deflected interstellar neutral hydrogen, thought to be controlled by the ISMF. Our results yield draped ISMF properties close to that observed by Voyager 1, the only spacecraft to directly measure the ISMF close to the heliosphere, and give predictions of the pristine ISMF that Voyager 1 has yet to sample.

Three-dimensional Features of the Outer Heliosphere Due to Coupling between the Interstellar and Heliospheric Magnetic Field. V. The Bow Wave, Heliospheric Boundary Layer, Instabilities, and Magnetic Reconnection

“…Such investigation should also be data-driven because the ISMF undraping observed by V1 strongly suggest that time-dependent phenomena are deeply involved in this process. Steady-state MHD-kinetic simulations presented here (see also Zirnstein et al 2016) show that such undraping should be monotone.…”

“…Figure 3 shows the plasma density distributions for the same set of parameters in the meridional plane. The LISM parameters are taken from our previous simulation in Zirnstein et al (2016), and are summarized in Table 1. For convenience, the V ∞ and B ∞ directions are also given in the J2000 ecliptic coordinates ( Table 2).…”

Effect of Supernovae on the Local Interstellar Material

“…The LIC magnetic field direction is found from the center of the IBEX ribbon arc of higher ENA fluxes, ℓ = 34.8 • ± 4.3 • , b = 56.6 • ± 1.2 • , which forms upwind of the heliopause where the ISMF draping over the heliosphere becomes perpendicular to the sightline [15,16,19]. The velocity of the LIC gas has been determined from IBEX in situ measurements of neutral interstellar He, H, and O flowing through the heliosphere [140,155,141,142] and corresponds to a LIC LSR velocity of 17.2 ± 1.…”

“…Figure 1 shows the distribution of interstellar material within ∼ 400 pc according to the cumulative reddening of starlight as measured by the color excess E(B-V) , [5], in preparation). Superimposed on the reddening maps are nearby superbubble shells, the interarm interstellar magnetic field (ISMF) indicated by pulsar data [14], and the local ISMF direction diagnosed by the Ribbon of energetic neutral atoms (ENAs) discovered by the Interstellar Boundary Explorer (IBEX) spacecraft [15,16,17,18,19]. The extinction void around the Sun, denoted the Local Bubble, occurs where the interior of Gould's Belt blends into the interarm regions of the third galactic quadrant.…”

Electromagnetic Forces on a Relativistic Spacecraft in the Interstellar Medium

“…The mean magnetic strength of ∼ 3µG is inferred from observations by Interstellar Boundary Explorer (IBEX) in Zirnstein et al (2016). The strength of interstellar magnetic field toward α Centauri is uncertain, but likely between 3 − 10µG.…”