  Gamma Cas analog sources are a subset of Be stars that emit intense and hard
X-ray emission. Two competing ideas for their X-ray production mechanism are
(a) the magnetic activities of the Be star and its disk and (b) the accretion
from the Be star to an unidentified compact object. Among such sources, Pi Aqr
plays a pivotal role as it is one of the only two spectroscopic binaries
observed for many orbital cycles and one of the three sources with X-ray
brightness sufficient for detailed X-ray spectroscopy. Bjorkman et al. (2002)
estimated the secondary mass > 2.0 Mo with optical spectroscopy, which would
argue against the compact object being a white dwarf (WD). However, their
dynamical mass solution is inconsistent with an evolutionary solution and their
radial velocity measurement is inconsistent with later work by Naze et al.
(2019). We revisit this issue by adding a new data set with the NuSTAR X-ray
observatory and the HIDES echelle spectrograph. We found that the radial
velocity amplitude is consistent with Naze et al. (2019), which is only a half
of that claimed by Bjorkman et al. (2002). Fixing the radial velocity amplitude
of the primary, the secondary mass is estimated as < 1.4 Mo over an assumed
range of the primary mass and the inclination angle. We further constrained the
inclination angle and the secondary mass independently by fitting the X-ray
spectra with a non-magnetic or magnetic accreting WD model under the assumption
that the secondary is indeed a WD. The two results match well. We thus argue
that the possibility of the secondary being a WD should not be excluded for pi
Aqr.
