RXTE Observations of New Black Hole Candidates XTE J1752-223 and MAXI   J1659-152
  We report the most recent results of our analysis of X-ray monitoring of new Galactic Black Hole (BH) candidates XTE J1752-225 and MAXI J1659-152 performed by Rossi X-ray Timing Explorer (RXTE). We investigate various aspects of the RXTE data including energy and power spectra, variability energy distribution and phase lags between soft and hard energy bands. The sources generally exhibit the spectral states and evolution expected from an accreting stellar mass BH. The energy distribution of different variability components show that the aperiodic noise has a spectrum consistently softer with respect to the total rms spectrum, while the spectrum of the quasi-periodic (QPO) features is harder. Particularly interesting behavior is observed in phase lags. Namely, XTE J1753-223 shows that QPO in the hard band lags the QPO in the soft band. This is opposite to what was previously reported in other bright BH candidates and also found in our analysis from MAXI J1659-152. We report the results of BH mass estimations using the spectral-timing correlation scaling technique. Namely, we obtain the BH masses of 9.5 +/-1.5 and 20+/-3 solar masses for XTE J1752-223 and MAXI J1659-152 correspondingly. 
Nikolai Shaposhnikov, Jean H. Swank, Craig Markwardt, and Hans Krimm
astro-ph.HE