GPS Timing and Control System of the HAWC Detector
  The design and performance of the GPS Timing and Control (GTC) System of the High Altitude Water Cerenkov (HAWC) gamma ray observatory is described. The GTC system provides a GPS synchronized absolute timestamp, with an accuracy better than 1$\mu$s, for each recorded event in HAWC. In order to avoid any slack between the recorded data and the timestamp, timestamps are injected to the main data acquisition (DAQ) system after the Front-end Electronic Boards (FEBs). When HAWC is completed, the HAWC main DAQ will use 10 time to digital converters (TDCs). In order to keep all the TDCs in sync, the GTC system provides a synchronized clock signal, coordinated trigger signal, and control signals to all TDCs. 
Anushka Udara Abeysekara, Tilan N. Ukwatta, Dan Edmunds, James   Linnemann, Asif Imran, Gerd Kunde, Ian Wisher
astro-ph.IM physics.ins-det