TY - JOUR
T1 - Interstellar Neutral Helium in the Heliosphere from IBEX Observations. V. Observations in IBEX-Lo ESA Steps 1, 2, and 3
AU - Swaczyna, Paweł
AU - Bzowski, Maciej
AU - Kubiak, Marzena A.
AU - Sokół, Justyna M.
AU - Fuselier, Stephen A.
AU - Galli, André
AU - Heirtzler, David
AU - Kucharek, Harald
AU - McComas, David J.
AU - Möbius, Eberhard
AU - Schwadron, Nathan A.
AU - Wurz, P.
N1 - Publisher Copyright:
© 2018. The American Astronomical Society. All rights reserved.
PY - 2018/2/20
Y1 - 2018/2/20
N2 - Direct-sampling observations of interstellar neutral (ISN) He by the Interstellar Boundary Explorer (IBEX) provide valuable insight into the physical state of and processes operating in the interstellar medium ahead of the heliosphere. The ISN He atom signals are observed at the four lowest ESA steps of the IBEX-Lo sensor. The observed signal is a mixture of the primary and secondary components of ISN He and H. Previously, only data from one of the ESA steps have been used. Here, we extend the analysis to data collected in the three lowest ESA steps with the strongest ISN He signal, for the observation seasons 2009-2015. The instrument sensitivity is modeled as a linear function of the atom impact speed onto the sensor's conversion surface separately for each ESA step of the instrument. We find that the sensitivity increases from lower to higher ESA steps, but within each of the ESA steps it is a decreasing function of the atom impact speed. This result may be influenced by the hydrogen contribution, which was not included in the adopted model, but seems to exist in the signal. We conclude that the currently accepted temperature of ISN He and velocity of the Sun through the interstellar medium do not need a revision, and we sketch a plan of further data analysis aiming at investigating ISN H and a better understanding of the population of ISN He originating in the outer heliosheath.
AB - Direct-sampling observations of interstellar neutral (ISN) He by the Interstellar Boundary Explorer (IBEX) provide valuable insight into the physical state of and processes operating in the interstellar medium ahead of the heliosphere. The ISN He atom signals are observed at the four lowest ESA steps of the IBEX-Lo sensor. The observed signal is a mixture of the primary and secondary components of ISN He and H. Previously, only data from one of the ESA steps have been used. Here, we extend the analysis to data collected in the three lowest ESA steps with the strongest ISN He signal, for the observation seasons 2009-2015. The instrument sensitivity is modeled as a linear function of the atom impact speed onto the sensor's conversion surface separately for each ESA step of the instrument. We find that the sensitivity increases from lower to higher ESA steps, but within each of the ESA steps it is a decreasing function of the atom impact speed. This result may be influenced by the hydrogen contribution, which was not included in the adopted model, but seems to exist in the signal. We conclude that the currently accepted temperature of ISN He and velocity of the Sun through the interstellar medium do not need a revision, and we sketch a plan of further data analysis aiming at investigating ISN H and a better understanding of the population of ISN He originating in the outer heliosheath.
KW - ISM: atoms
KW - ISM: kinematics and dynamics
KW - Sun: heliosphere
KW - instrumentation: detectors
KW - local interstellar matter
KW - methods: data analysis
UR - http://www.scopus.com/inward/record.url?scp=85042719134&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=85042719134&partnerID=8YFLogxK
U2 - 10.3847/1538-4357/aaabbf
DO - 10.3847/1538-4357/aaabbf
M3 - Article
AN - SCOPUS:85042719134
SN - 0004-637X
VL - 854
JO - Astrophysical Journal
JF - Astrophysical Journal
IS - 2
M1 - 119
ER -