Colloquium on Jun. 11, 2026

Probing Outbursting Black Hole X-ray Binaries with Multiwavelength Observations

Speaker: Guobao Zhang (YNAO)

Venue: SWIFAR Building 2111

Time: 16:00 PM, Thursday, Jun. 11, 2026

Abstract:

The emission from accreting black holes (BHs) in low-mass X-ray binaries (LMXBs) spans a broad energy range from radio to X-rays, and multi-wavelength observations provide a powerful probe of accretion physics. In this talk, I will present recent studies of the BH-LMXBs Swift J1753.5–0127 and MAXI J1820+070, focusing on the evolution of accretion discs throughout the outburst cycle. Long-term simultaneous UV/optical and X-ray observations of Swift J1753.5–0127 reveal flux correlations consistent with emission dominated by a viscously heated outer accretion disc, while deviations from these trends indicate changes in the inner accretion flow. I will also discuss evidence for an enhanced mass supply to the outer accretion disc prior to the hard-to-soft state transition in MAXI J1820+070, suggesting that variations in mass transfer may play an important role in driving state changes. Finally, observations of the bright mini-outburst that preceded the end of the 12-year activity of Swift J1753.5–0127 indicate that a cooling wave, triggered as the outer disc approached the critical temperature predicted by the disc instability model, ultimately terminated the outburst. Together, these results provide new insights into the roles of disc evolution, mass-transfer variability, and thermal-viscous instabilities in shaping the outburst behaviour of BH-LMXBs.

Report PPT:  SWIFAR_Guobao Zhang.pdf