[Paper Review] RXTE Observations of New Black Hole Candidates XTE J1752-223 and MAXI J1659-152

Nikolai Shaposhnikov, J. H. Swank+2 more|arXiv (Cornell University)|Mar 2, 2011

Astrophysical Phenomena and Observations3 citations

TL;DR

This paper presents RXTE observations of two new galactic black hole candidates, XTE J1752-223 and MAXI J1659-152, analyzing their timing and spectral evolution during outbursts. Using the scaling method based on the correlation between spectral index and quasi-periodic oscillation (QPO) frequency, it derives a black hole mass of 20 ± 3 M☉ for J1659—among the highest measured for a Galactic black hole—suggesting an ultra-compact binary system with a possible 2.4-hour orbital period.

ABSTRACT

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.

Motivation & Objective

• To analyze the timing and spectral evolution of two newly discovered galactic black hole candidates, XTE J1752-223 and MAXI J1659-152, during their outbursts.
• To investigate the nature of quasi-periodic oscillations (QPOs) and their correlation with spectral parameters in black hole binaries.
• To determine black hole masses using the scaling method based on the QPO frequency–spectral index correlation.
• To test the robustness of the index saturation effect as a signature of black hole accretion physics across different sources.

Proposed method

• Performed Fourier analysis on RXTE/PCA data to extract power density spectra (PDS), rms spectra, and time lags between energy bands.
• Used the method of Fourier-resolved spectroscopy to study energy-dependent variability and phase lags in 1.5–5 keV and 10–12 keV bands.
• Applied the bulk motion Comptonization (BMC) model to fit spectra, including interstellar absorption and high-energy cutoff components.
• Utilized the QPO-frequency–spectral-index correlation to scale observed data from J1659 to reference data from GX 339-4 during its 2003 decay outburst.
• Calculated scaling coefficients $ s_\nu = \nu_{\text{GX339-4}} / \nu_{\text{J1659}} = 1.62 \pm 0.03 $ and $ s_N = N_{\text{GX339-4}} / N_{\text{J1659}} = 1.08 \pm 0.03 $ for mass and distance estimation.
• Assumed a geometrical factor of unity and applied known distance and mass of GX 339-4 (12.3 ± 1.4 M☉, 5.8 ± 0.7 kpc) to infer parameters for J1659.

Experimental results

Research questions

• RQ1 What is the nature of the QPO and its evolution during the hard-to-soft state transition in XTE J1752-223 and MAXI J1659-152?
• RQ2 How do time lags and rms spectra vary across energy bands during different states of the outburst?
• RQ3 Can the QPO-spectral index correlation be used to reliably estimate black hole masses in new candidates?
• RQ4 What does the observed saturation of the spectral index at high QPO frequencies imply about accretion flow structure?
• RQ5 What are the implications of a 20 M☉ black hole mass in MAXI J1659-152 for binary evolution and compact binary systems?

Key findings

• The spectral index in J1659 saturates at 2.3 during the hard-to-soft state transition, indicating a strong signature of bulk motion Comptonization (BMC) and consistent with a black hole origin.
• The black hole mass in MAXI J1659-152 is estimated at 20 ± 3 M☉ using the scaling method, making it the most massive stellar-mass black hole measured in the Galaxy to date.
• The inferred distance to J1659 is 7.6 ± 1.1 kpc, though this is likely an upper limit due to the high inclination inferred from X-ray dips.
• The QPO frequency in J1659 evolves from below 0.1 Hz to 10 Hz during the state transition, consistent with a compact accretion flow and strong gravitational effects.
• The time lags observed during the hard intermediate state are positive (harder photons lag), while they become negative during the soft intermediate state, suggesting a transition from Comptonization to jet/outflow dominance.
• The index-QPO frequency correlation in J1659 shows one of the most pronounced saturations among galactic black hole candidates, supporting its identification as a black hole.