Nanosecond-level time synchronization of autonomous radio detector stations for extensive air showers

THE PIERRE AUGER COLLABORATION, INCLUYE S. MOLLERACH

JOURNAL OF INSTRUMENTATION

IOP PUBLISHING LTD

Lugar: Londres; Año: 2016 vol. 11

1748-0221

To exploit the full potential of radio measurements of cosmic-ray airshowers at MHz frequencies, a detector timing synchronization within 1ns is needed. Large distributed radio detector arrays such as the AugerEngineering Radio Array (AERA) rely on timing via the Global PositioningSystem (GPS) for the synchronization of individual detector stationclocks. Unfortunately, GPS timing is expected to have an accuracy nobetter than about 5 ns. In practice, in particular in AERA, the GPSclocks exhibit drifts on the order of tens of ns. We developed atechnique to correct for the GPS drifts, and an independent method isused to cross-check that indeed we reach a nanosecond-scale timingaccuracy by this correction. First, we operate a ``beacon transmitter''which emits defined sine waves detected by AERA antennas recorded withinthe physics data. The relative phasing of these sine waves can be usedto correct for GPS clock drifts. In addition to this, we observe radiopulses emitted by commercial airplanes, the position of which wedetermine in real time from Automatic Dependent Surveillance Broadcastsintercepted with a software-defined radio. From the known sourcelocation and the measured arrival times of the pulses we determinerelative timing offsets between radio detector stations. We demonstratewith a combined analysis that the two methods give a consistent timingcalibration with an accuracy of 2 ns or better. Consequently, the beaconmethod alone can be used in the future to continuously determine andcorrect for GPS clock drifts in each individual event measured by AERA.