Final Report Summary - JETVAR (Multiwavelength variability study of the jet variability in X-ray binaries.) Jets appear to be ubiquitous in accreting systems, but the origin of the observed accretion disc-jet coupling remain largely unknown. In this project we had proposed to use a twofold, observational and theoretical, approach to study and understand the internal physics, structure and variability of jets in accreting compact objects. The main objective of the project was to take advantage of newly available technologies of fast photometers on large telescopes, to study, for the first time, fast multi-wavelength variability in accreting compact objects. At the same time, we planned to support these observations with a deep theoretical effort, modelling the multi-wavelength variable emission from a mildly-relativistic jet. The project evolved smoothly and overall successfully. The fellow submitted and accepted a number of observing proposals, to observe accreting compact objects during different phases of their evolution. This allowed us to collect a large amount of data at different wavelengths and of different types of objects, from black-hole to neutron-star X-ray binaries, both in outburst and in quiescence. Some datasets have been already published (with the fellow being the first author or one of the main co-authors of the publications), and important results have been achieved, including the first independent estimate of the magnetic field in a jet, a model-dependent estimate of the jet speed, as well as the discovery of the first highly-variable self-absorption break. A large effort to assembly a dedicated software has been started, and all acquired datasets are currently under analysis, and soon to be published. The theoretical approach has been also pursued. A new model for the spectral emission of a mildly-relativistic jet has been developed and published by the fellow and one of his collaborators, and a first follow-up paper has been published with the fellow being the first author. Further work is in progress, and to be published soon. Overall, the project has been fully successful in starting what is now considered a new field, which has already met the interest of the international community. The results obtained within this project have been presented and discussed at several international conferences. These topics are also part of the science case of at least one space mission, LOFT, which has been recently selected by ESA to access to the assessment for M3 missions. Both the fellow and myself (the coordinator) are active members of this large international collaboration.
