ANTARES time calibration

The ANTARES Collaboration has recently completed the construction of an underwater neutrino telescope located at 2475 km depth, 40 km away from the Toulon coast in France. The final detector consists of 885 photomultipliers (PMTs) distributed along 12 lines. At present, the deployed detector is the largest neutrino telescope in the northern hemisphere. The aim of ANTARES is the detection of cosmic neutrinos. A good angular resolution, which relies on a good time resolution and positioning, is required to identify the neutrino sources. In this contribution, we review the ANTARES time calibration systems, namely: (1) the on-shore dark room calibration, which allows the measurement of the relative time offsets among PMTs, (2) the echo-based clock system, which enables the measurement of the time delay of the signal from the clock board located on each storey to the shore station, (3) the internal LED, which monitors the PMTs transit time, (4) the Optical Beacons (OBs), which send light pulses that enable the relative time calibration of PMTs, and (5) the K40 calibration which together with the OBs allow a determination of time differences among PMTs of the same storey. These systems have shown that the required time resolution is achieved. Moreover, they ensure that the relative time offsets among PMTs are properly computed and, therefore, enable an optimized track reconstruction. The experience gained with ANTARES in the issue of time calibration is of great value in the design of the corresponding system for a VLVNT in the Mediterranean Sea.