Payaswini Saikia

Accretion and jet formation in black holes are scale-invariant processes, postulated to be governed by fundamental laws that operate consistently across the full mass spectrum — from stellar-mass black holes in X-ray binaries (XRBs) to supermassive black holes in active galactic nuclei (AGN). A cornerstone of this phenomenon is the Fundamental Plane of Black Hole Activity, which studies coupling between accretion and ejection by linking black hole mass with radio, optical and X-ray luminosities in a well-defined correlation. In this seminar, I will examine the observational evidence for scale invariance and disc-jet coupling with cutting-edge multi-wavelength studies. I will present our long-term optical monitoring of around 50 low-mass XRBs, using the Las Cumbres Observatory global robotic network. For these systems, often detectable only during X-ray outbursts, low-level accretion have recently been detected even during their quiescence. I will introduce our real-time monitoring pipeline, XB-NEWS, and highlight the potential of optical data in uncovering the mechanistic details of these outburst cycles and in testing the predictions of the disc-instability model. Moving on to the supermassive black holes, I will focus on our expansive VLBA survey of the JWST North Ecliptic Pole Time-Domain Field, strategically targeting the faint radio sources identified with the VLA. At VLBA’s sub-milliarcsecond resolution and µJy sensitivity, we detect compact non-thermal emission in a subset of sources, consistent with AGN jets or coronae. I will discuss measurements of the host galaxy properties using JWST and WISE data, and outline future directions, including radio follow-up with GMRT, to further disentangle AGN activity from star formation. Spanning from galactic binaries to extragalactic AGN, in this talk I will explore the unifying physics behind black hole accretion and jet production across the mass scale.