Lunch talk on May. 5, 2023

Multi-wavelength studies of the X-ray binary MAXI J1727-203: constraining system parameters

Speaker:Sili Wang (RCSCE at Ehime University)

Venue:SWIFAR Building 2111

Time:12:30 PM, Friday, May. 5, 2023

Abstract:

The X-ray fluxes of black hole candidates (BHCs) usually exceed their quiescent levels by many orders of magnitude at their outbursts. Many BHCs exhibit state transitions, associated with changes in their X-ray fluxes during their outbursts. The presence of two different ``states" (the low/hard state and the high/soft state) in the X-ray emissions of the first BHC, Cyg X-1, was discovered in the early 1970s. Since then, more BHCs (e.g. GX 399-4, GS 2000+251) have been observed to exhibit one or both of these states. Analyzing state transitions of a BHC can help us understand the physics of black hole accretion flows over a wide range of mass accretion rate. MAXI J1727-203, a BHC, was first detected in X-ray outburst in June 2018 (Yoneyama et al. 2018). This source has not been well studied yet, leaving blank information of credible constraints on the system parameters, such as inclination, spin and source distance. In this study, We report on the evolution of X-ray spectral and timing properties of MAXI J1727-203 based on NICER/XTI and MAXI/GSC observations. Over the course of the outburst, a transition from the intermediate state to the high/soft state, and then back to the low/hard state was observed. During the high/soft state, a typical constant innermost radius of accretion disk was seen. Assuming that this system contain a Schwarzschild black hole and has an inclination angle of 0-84 degree, and considering the typical Eddington ratio at the transition back to the low/hard state, the black hole mass was estimated to be $M\geq11.5\ \mathrm{M_{\odot}}$ for a distance of $D\geq 5.9$ kpc. We also attempted to constrain the black hole mass and distance with a different method by combining the results from optical and near-infrared photometric observations. We modeled the near-infrared to X-ray spectral energy distributions obtained in the outburst period with an irradiated disk model, and estimated the lower limit of the black hole mass for a given distance, assuming both accretion disk and companion star fill their Roche lobe. The lower limit was, however, found to be much higher than the constraint obtained from the X-ray data. We discuss several possible causes of this inconsistency.

Report PPT:SWIFAR_Sili Wang.pptx