Authors: Bishwas L. Shrestha (Princeton University), Eric J. Zirnstein (Princeton University), David J. McComas (Princeton University)

Interstellar Pickup ions (PUIs) are created by ionization of the interstellar neutral atoms by charge exchange, photoionization, and electron impact ionization in the heliosphere. As the PUIs travel outward with the expanding solar wind, they are occasionally heated by passing interplanetary shocks and sometimes form a suprathermal power-law tail. PUIs are preferentially heated at distant interplanetary shocks and dominate the internal pressure in the outer heliosphere. Additionally, PUIs are likely preferentially heated at the heliospheric termination shock (HTS) and believed to be the primary source of ~0.5-7 keV ions in the inner heliosheath. PUIs are the parent population of energetic neutral atoms created beyond the HTS that is being observed by NASA’s Interstellar Boundary Explorer. In this study, we present observations of suprathermal PUI tails downstream of interplanetary shocks using the SWAP data over a heliocentric distance of ~23.5-37 au. We show how the observed number density of suprathermal PUI tails varies with the shock compression ratio. These results are then compared with the theoretical estimate of reflected PUI number density based on the electrostatic cross-shock potential.