  Direct-sampling observations of interstellar neutral (ISN) He by 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 extended 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 found 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.
