Speaker
Description
GRS 1915+105, the low mass X-ray binary with the largest accretion disk and the first microquasar observed with superluminal jets, has stayed in a high-luminosity outburst for decades since its discovery in 1992. However, in mid 2018, the source entered a new phase in which the X-rays suddenly dropped to an unprecedentedly low flux that was quickly followed by a rebrightening in the radio, breaking the phenomenological X-ray – radio correlation that links the accretion flow and jets. Multi-wavelength observations suggest that this low X-ray state is the result of a complex layer of absorbing material, whose exact nature remains unknown. Milliarcsecond-resolution radio imaging allows us to probe the jet direction and its behaviour at the base during this unprecedented phase in the lifetime of GRS 1915+105.
I will present four radio Very Long Baseline Interferometry (VLBI) epochs during this X-ray obscured phase that reveal highly variable radio behaviour, including flaring within our observations and the launch of discrete ejecta. By applying a time-dependent model fitting approach directly to the visibility data we put tight constraints on the ejecta’s speeds and ejection times, which we compare to corresponding features in the accretion flow.
Remarkably, we detect a large swing in the jet direction (up to 59° ± 2° with respect to the last VLBI observation from 2006), something that hasn't been observed in GRS 1915+105 prior to the obscured state. This makes GRS 1915+105 the only microquasar found to exhibit both precessing and fixed-direction extended jets. The presence of both jet types has implications for a recently proposed jet paradigm, distinguishing precessing, slow jets and fixed, fast jets locked onto the black hole spin-axis. I will discuss potential mechanisms that link this abrupt, milliarcsecond jet precession to the X-ray obscuration phase, including a ULX analogy and radiative warping.
| Talk category | NOVA Network 3 |
|---|---|
| PhD relevance | 2nd |
