Interstellar Neutral Helium in the Heliosphere from IBEX Observations. I. Uncertainties and Backgrounds in the Data and Parameter Determination Method

Abstract

This paper is one of three companion papers presenting the results of our in-depth analysis of the interstellar neutral helium (ISN He) observations carried out using the IBEX-Lo during the first six Interstellar Boundary Explorer (IBEX) observation seasons. We derive corrections for losses due to the limited throughput of the interface buffer and determine the IBEX spin-axis pointing. We develop an uncertainty system for the data, taking into account the resulting correlations between the data points. This system includes uncertainties due to Poisson statistics, background, spin-axis determination, systematic deviation of the boresight from the prescribed position, correction for the interface buffer losses, and the expected Warm Breeze (WB) signal. Subsequently, we analyze the data from 2009 to examine the role of various components of the uncertainty system. We show that the ISN He flow parameters are in good agreement with the values obtained by the original analysis. We identify the WB as the principal contributor to the global ${\chi }^2$ values in previous analyses. Other uncertainties have a much milder role and their contributions are comparable to each other. The application of this uncertainty system reduced the minimum ${\chi }^2$ value 4-fold. The obtained ${\chi }^2$ value, still exceeding the expected value, suggests that either the uncertainty system may still be incomplete or the adopted physical model lacks a potentially important element, which is likely an imperfect determination of the WB parameters. The derived corrections and uncertainty system are used in the accompanying paper by Bzowski et al. in an analysis of the data from six seasons.

43 pages, 9 figures

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Cited by in corpus (17)

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• Interstellar neutral helium in the heliosphere from IBEX observations. IV. Flow vector, Mach number, and abundance of the Warm Breeze
• Interstellar neutral helium in the heliosphere from IBEX observations. II. The Warsaw Test Particle Model (WTPM)
• Interstellar neutral helium in the heliosphere from IBEX observations. VI. The He${}^{+}$ density and the ionization state in the Very Local Interstellar Matter
• The helium Warm Breeze in IBEX observations as a result of charge exchange collisions in the outer heliosheath
• Interstellar neutral helium in the heliosphere from IBEX observations. V. Observations in IBEX-Lo ESA steps 1, 2, & 3
• Very Local Interstellar Medium Revealed by Complete Solar Cycle of Interstellar Neutral Helium Observations with IBEX
• Distance to the IBEX Ribbon Source Inferred from Parallax
• The Interstellar Neutral He haze in the heliosphere: what can we learn?
• Mixing Interstellar Clouds Surrounding the Sun
• Slowdown and Heating of Interstellar Neutral Helium by Elastic Collisions Beyond the Heliopause
• Interstellar Conditions Deduced from Interstellar Neutral Helium Observed by IBEX and Global Heliosphere Modeling
• Evidence for Asymmetry in the Velocity Distribution of the Interstellar Neutral Helium Flow Observed by IBEX and Ulysses
• Science Opportunities from Observations of the Interstellar Neutral Gas with Adjustable Boresight Direction
• Synthesis of the distribution function of ISN He
• Stability of the interstellar hydrogen inflow longitude from 20 years of SOHO/SWAN observations
• Relative In-flight Response of IBEX-Lo to Interstellar Neutral Helium Atoms