With the recent detection of high energy astrophysical neutrinos by the IceCube experiment and of gravitationnal waves by the LIGO and Virgo interferometers, the multimessenger astronomy era has effectively begun. The joint observation of the violent « non thermal » Universe with different messenger will in particular help solving the question of the origin of Cosmic Rays by the study of the most energetic phenomena as Supernovae, Active Galactic Nuclei or Gama Ray Bursts. Neutrinos play a crucial role in this picture as they enable to unambiguously trace high energy hadronic interactions, and hence cosmic ray acceleration, in the heart of the sources.  Their exclusively weak interaction nature makes them extremely hard to detect, making necessary the instrumentation of huge natural transparent media volumes like see or ice at great depth, but experiments are reaching nowadays the necessary sensitivity to detect the first individual sources after the observation of a diffuse astrophysical emission by IceCube. With a better angular resolution than ice-based detectors the ANTARES neutrino telescope in operation since 2008 and it’s successor KM3NeT currently in construction in the depth of the Mediterranean have the potential to pinpoint individual sources, and even more so when in conjonction with other detectors. The APC ANTARES/KM3NeT group has a long experience in multi-messenger studies, benefiting from the proximity of local colleagues working on gravitational waves, cosmic ray phenomenology  or high energy photons. The search for transient sources allows to improve the detection efficiency of detectors by requiring space and time coincidence between the signals of different messengers, and the group has been pioneering the searches for joint gravitational waves and high energy neutrino emitters. Taking data during the forthcoming the observational data taking runs of the LIGO and Virgo detectors, ANTARES and then KM3Net offer the possibility to explore a population of sources undetectable or very weak in photons like failed and ultraweak GRBs. The PhD student will perform a search for high energy neutrino transients in the final data set of the ANTARES neutrino telescope incorporating informations of other messengers, in particular gravitational waves, to enhence both detector sensitivity. In addition, the candidate will have the opportunity to participate actively  to the analysis of the first data of the next generation telescope KM3NeT currently under construction in the Mediterranean Sea.