Speaker
Description
Fast multi-wavelength studies of black hole transients are revealing a complex and rich phenomenology, opening a new era in the study of disc-jet coupling. In this talk, I will show the latest results regarding an X-ray/Optical and infrared (O-IR) campaign on the bright transient Swift J1727.8-1613. By following the source with NICER, Ultracam HAWKI, and HIPERCAM, for the first time, we were able to track the evolution of a QPO in X-ray and O-IR band during the state transition. In particular, during our three observations, we observed a drift in the QPO from 1.4 Hz to 4 Hz. These are among the highest O-IR QPO frequencies detected for a black hole X-ray transient. During the first two epochs, the X-ray and O-IR emissions are correlated, with an optical lag (compared to the X-rays) varying from +70 ms to 0 ms. Finally, during the third epoch, we measured for the first time, a lag of the $z_s$-band respect to the $g_s$-band at the QPO frequency ($\approx$+10 ms). By estimating the variable O-IR SED we find that the emission is most likely non-thermal. I will show how these observations challenge our state-of-the-art models showing that neither the jet nor the hot flow model can easily explain the observed evolution of the QPOs.
| Contribution | Oral talk |
|---|---|
| Affiliation | INAF-IAPS |
| vincentelli.astro@gmail.com |
