Synchronous X-ray/Optical QPOs from the Black Hole LMXB MAXI J1820+070

TL;DR

This study reports simultaneous optical and X-ray observations of the black hole binary MAXI J1820+070, revealing evolving QPOs and complex lag patterns, supporting a precessing jet model for their origin.

Contribution

It provides the first detailed analysis of synchronized optical and X-ray QPOs and their evolution in MAXI J1820+070, proposing a jet precession explanation.

Findings

Optical QPOs increase in frequency during outburst.

X-ray and optical QPOs are synchronized with constant phase lag.

Complex lag patterns include anti-correlation and sub-second lags.

Abstract

We present high-speed optical photometry from SAAO and SALT on the black hole LMXB \MAXI (ASSASN-18ey), some of it simultaneous with NICER, Swift and Insight-HXMT X-ray coverage. We detect optical Quasi-Periodic Oscillations (QPOs) that move to higher frequencies as the outburst progresses, tracking both the frequency and evolution of similar X-ray QPOs previously reported. Correlated X-ray/optical data reveal a complex pattern of lags, including an anti-correlation and a sub-second lag that evolve over the first few weeks of outburst. They also show correlated components separated by a lag equal to the QPO period roughly centered on zero lag, implying that the inter-band variability is strongly and consistently affected by these QPOs at a constant phase lag of roughly +/- pi. The synchronisation of X-ray and optical QPOs indicates that they must be produced in regions physically very close to each other; we thus propose that they can be explained by a precessing jet model, based on analogies with V404 Cyg and MAXI J1348-630.