Using X-ray continuum-fitting to estimate the spin of MAXI J1305-704

MAXI J1305-704 is a transient X-ray binary with a black hole primary. It was discovered on April 9, 2012, during its only known outburst. MAXI J1305-704 is also a high inclination low-mass X-ray binary with prominent dip features in its light curves, so we check the full catalog of 92 \emph{Swift}/XRT continuous observations of MAXI J1305-704, focusing only on the stable spectra. We select 13 gold" spectra for which the root mean square RMS <0.075 and the coronal scattered fraction $f_{\mathrm{sc}} \lesssim 25 \%$. These gold" data are optimal thermal-state observations for continuum-fitting modeling, in which the disk extends to the innermost-stable circular orbit and is geometrically thin. The black hole spin was unknown for this object before. By utilizing the X-ray continuum fitting method with the relativistic thin disk model $\mathtt{\text{kerrbb2}}$ and supplying the known dynamical binary system parameters, we find MAXI J1305-704 has a moderate spin ($a_{\ast }=0.87_{-0.13}^{+0.07}$) at a 68.3% confidence level. This is the first determination of MAXI J1305-704’s spin.