  To date, close to fifty presumed black hole binary mergers were observed by
the LIGO and Virgo detectors. The analyses have been done with an assumption
that these objects are black holes by limiting the spin prior to the Kerr
bound. However, the above assumption is not valid for superspinars, which have
the Kerr geometry but rotate beyond the Kerr bound. In this study, we
investigate whether and how the limited spin prior range causes a bias in
parameter estimation for superspinars if they are detected. To this end, we
estimate binary parameters of the simulated inspiral signals of the
gravitational waves of compact binaries by assuming that at least one component
of them is a superspinar. We have found that when the primary is a superspinar,
both mass and spin parameters are biased in parameter estimation due to the
limited spin prior range. In this case, the extended prior range is strongly
favored compared to the limited one. On the other hand, when the primary is a
black hole, we do not see much bias in parameter estimation due to the limited
spin prior range, even though the secondary is a superspinar. We also apply the
analysis to black hole binary merger events GW170608 and GW190814, which have a
long and loud inspiral signal. We do not see any preference of superspinars
from the model selection for both events. We conclude that the extension of the
spin prior range is necessary for accurate parameter estimation if highly
spinning primary objects are found, while it is difficult to identify
superspinars if they are only the secondary objects. Nevertheless, the bias in
parameter estimation of spin for the limited spin prior range can be a clue of
the existence of superspinars.
