Nanosecond-level time synchronization of autonomous radio detector stations using a reference beacon and commercial airplanes

A ALMELA; THE PIERRE AUGER COLLABORATION

JOURNAL OF INSTRUMENTATION

IOP PUBLISHING LTD

Lugar: Londres; Año: 2015

1748-0221

To exploit the full potential of radio measurements of cosmic-ray air showersat MHz frequencies, a detector timing synchronization within 1 ns is needed.Large distributed radio detector arrays such as the Auger Engineering RadioArray (AERA) rely on timing via the Global Positioning System (GPS) for thesynchronization of individual detector station clocks. Unfortunately, GPStiming is expected to have an accuracy no better than about 5 ns. In practice,in particular in AERA, the GPS clocks exhibit drifts on the order of tens ofns. We developed a technique to correct for the GPS drifts, and an independentmethod used for cross-checks that indeed we reach nanosecond-scale timingaccuracy by this correction. First, we operate a "beacon transmitter" whichemits defined sine waves detected by AERA antennas recorded within the physicsdata. The relative phasing of these sine waves can be used to correct for GPSclock drifts. In addition to this, we observe radio pulses emitted bycommercial airplanes, the position of which we determine in real time fromAutomatic Dependent Surveillance Broadcasts intercepted with a software-definedradio. From the known source location and the measured arrival times of thepulses we determine relative timing offsets between radio detector stations. Wedemonstrate with a combined analysis that the two methods give a consistenttiming calibration with an accuracy of 2 ns or better. Consequently, the beaconmethod alone can be used in the future to continuously determine and correctfor GPS clock drifts in each individual event measured by AERA.