Baikal-GVD: Time Calibrations in 2016

In April 2015, the first part (cluster) of the newly constructed next-generation neutrino telescope, Gigaton Volume Detector (GVD), was put into operation in the lake Baikal and started with data taking followed by another cluster installed in April 2017 thus doubling the number of installed Optical Modules (OMs) and instrumented volume. Moreover, the substantial extension of this detector is planned in the next few years. Specifically, another two clusters are going to be installed every consecutive year. In total 8 clusters consisting of 2304 OMs with overall effective volume ~0.4 km3 is going to be deployed by 2020. The vital condition for high angular resolution of reconstructed tracks of particles detected in GVD is a precise timing of individual channels which can be achieved with specialized time calibration systems. In this article, the different light sources and procedures used for time calibration of the GVD in the past as well as the newly developed ones are described and the results of the 2016 time calibration of the cluster Dubna are presented, especially the precision of intra and intersection calibrations and variations of calibration parameters in time.