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\section{Spinning Analysis}
\label{sec:spin}
\citet{Singer_2014} details the detection, low-latency localization, and medium-latency (i.e. non-spinning) follow-up of the simulated signals in 2015. Missing from the study is the complete characterization of sources, accounting for the spins of the NSs and their degeneracies with other parameters. In this work, we simulate this final step in the detection and characterization of BNS signals using the
``SpinTaylorT4'' SpinTaylorT4 fifteen-dimensional model for the GWs emitted by generically spinning, cicularized compact binary mergers \citep{Buonanno_2003,Buonanno_2009}.
The simulated population of BNS systems contains
very slowly spinning neutron stars, with spin magnitudes $\chi < 0.05$. This choice was motivated by the charactistics of neutron stars found in BNS systems to date. However, neutron stars \emph{outside} of BNS systems have been observed with spins as high as $\chi = 0.4$ \citep{Hessels_2006,Brown_2012}, and depending on the NS equation of state (EOS) could have spins as high as $\chi \lesssim 0.7$ \citep{Lo_2011} without breaking up. Thus, resticting priors to the narrow spin range used for the simulated population, could result in significant biases in parameter estimates if neutron stars with higher spins exist.
Though the main purpose of this study is to quantify parameter estimates while accounting for spin, we will include two non-spinning analyses for comparison. The first is the analysis using the
``TaylorF2'' TaylorF2 frequency-domain model, the results of which were presented in \citet{Singer_2014}. This model is fast, cheap to generate, and is always used for medium-latency follow-up before more expensive analyses are done. The second non-spinning analysis uses the time-domain
``SpinTaylorT4'' SpinTaylorT4 model, with spins fixed to $0$. This is not typically used in a follow-up scenario, but is included to demonstrate that any differences between the spinning and
``TaylorF2'' TaylorF2 analyses are due to the inclusion of spin, and not systematic differences between waveform models.
When analyzing a GW trigger, the Bayesian analyses use uninformative priors for the sources' properties. For some parameters, such as the location and orientation of the binary, uniformative priors (i.e. uniform in volume and isotropically oriented) are well-motivated. For other parameters (e.g., component masses, spins), current observations and theory do not motivate any particular choice in prior. For this
study study, we use a prior distribution uniform in component masses, as in \citet{2013arXiv1304.0670L}, and
use a prior with isotropically-oriented spins with magnitudes uniformly distributed between $0$ and
$1$ and isotropically oriented. $1$. We chose not to rule out compact objects with high spins because, since using any particular upper bound for spin magnatude would require assumptions regarding the unknown EOS of neutron stars.
An upper limit of $1$ is used as, in addition to safely emcompassing the spins permitted using various EOSs, this corresponds to the maximal value for black holes. In section \ref{subsec:prior_constraints}, we look at more constraining spin priors, and particularly how such choices can affect mass estimates.
