Long-Term Monitoring of the Black Hole Binary GX 339−4 in the High/Soft State during the 2010 Outburst with MAXI/GSC

Abstract

We present the results of monitoring the galactic black hole candidate GX 339 $-$ 4 with the Monitor of All-sky X-ray Image (MAXI) / Gas Slit Camera in the high/soft state during an outburst in 2010. All of the spectra throughout the 8-month period were well reproduced with a model consisting of multi-color disk emission and its Comptonization component, whose fraction is $\leq\ $ 25% in the total flux. In spite of the flux variability over a factor of 3, the innermost disk radius is constant at $R_{\rm in}$$=$ 61 $\ \pm\ $ 2 km for an inclination angle of $i$$=$ 46 $^\circ$ and a distance of $d$$=$ 8 kpc. This $R_{\rm in}$ value is consistent with those of past measurements with Tenma in the high/soft state. Assuming that the disk extends to the innermost stable circular orbit of a non-spinning black hole, we estimate the black hole mass to be $M$$=$ 6.8 $\ \pm\ $ 0.2 $\ M_{\odot}$ for $i$$=$ 46 $^\circ$ and $d$$=$ 8 kpc, which is consistent with that estimated from the Suzaku observation of the previous low/hard state. Further combined with the mass function, we obtained a mass constraint of 4.3 $\ M_\odot$$<$$M$$<$ 13.3 $\ M_\odot$ for the allowed range of $d$$=$ 6–15 kpc and $i$$<$ 60 $^\circ$ . We also discuss the spin parameter of the black hole in GX 339 $-$ 4 by applying relativistic accretion disk models to the Swift/XRT data.