Combined Spectral and Timing Analysis of the Black Hole Candidate MAXI J1659-152, Discovered by MAXI and Swift

We report on X-ray spectral and timing results of a new black hole candidate (BHC), MAXI J1659� 152, with an orbital period of 2.41hr (shortest among BHCs) in a 2010 outburst from 65 Rossi X-ray Timing Explorer (RXTE) observations and 8 simultaneous Swift and RXTE observations. According to the definitions of the spectral states in Remillard and McClintock (2006, ARA&A, 44, 49), most of the observations have been classified into the intermediate state. All of the X-ray broadband spectra can be modeled by a multi-color disk plus a power-law with an exponential cutoff or a multi-color disk plus a Comptonization component. During the initial phase of the outburst, a high-energy cutoff was visible at 30‐40keV. The innermost radius of the disk gradually decreased by a factor of more than 3 from the onset of the outburst, and reached a constant value of 35 d10cos i � 1=2 km, where d10 is the distance in units of 10kpc and i is the inclination. The type-C quasi-periodic oscillation (QPO) frequency varied from 1.6Hz to 7.3Hz in association with a change of the innermost radius, while the innermost radius remained constant during the type-B QPO detections at 1.6‐4.1Hz. Hence, we suggest that the origin of the type-B QPOs is differentfromthatoftype-CQPOs, thelatter of whichwould originatefromthedisk truncationradius. Assuming the constant innermostradius in the latter phase of the outburstas the innermoststable circular orbit, the black hole mass in)