Searching for the most elusive X-ray transients with XMM-Newton

Thanks to its unprecedented grasp in the 0.2-12 keV range and more than 16 years of operations, XMM-Newton EPIC is the best instrument to discover X-ray transient sources on timescales shorter than a few hours. However, many transients are missed by standard analysis procedures either because they are buried in the background of the full observation or because they occurred in high particle background time intervals. In the framework of EXTraS, an EU funded project aimed at the full exploitation of the EPIC data in the time domain, we developed a software pipeline to perform time-resolved source detection of EPIC archival data, leading us to the discovery of many new transient sources. After the software optimization and a careful screening of the results, the full transient catalogue and the software tools necessary to extend this search to forthcoming data will be made publicly available through an interactive archive and a science gateway, respectively. I will present the most interesting scientific cases we have already identified, ranging from flares of young stellar objects to extragalactic transients, their impact on our understanding of transient phenomena and the prospects for extending this analysis until the end of the XMM-Newton mission.