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

Abstract

To exploit the full potential of radio measurements of cosmic-ray air showers at MHz frequencies, a detector timing synchronization within 1 ns is needed. Large distributed radio detector arrays such as the Auger Engineering Radio Array (AERA) rely on timing via the Global Positioning System (GPS) for the synchronization of individual detector station clocks. Unfortunately, GPS timing 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 of ns. We developed a technique to correct for the GPS drifts, and an independent method is used to cross-check that indeed we reach a nanosecond-scale timing accuracy by this correction. First, we operate a "beacon transmitter" which emits defined sine waves detected by AERA antennas recorded within the physics data. The relative phasing of these sine waves can be used to correct for GPS clock drifts. In addition to this, we observe radio pulses emitted by commercial airplanes, the position of which we determine in real time from Automatic Dependent Surveillance Broadcasts intercepted with a software-defined radio. From the known source location and the measured arrival times of the pulses we determine relative timing offsets between radio detector stations. We demonstrate with a combined analysis that the two methods give a consistent timing calibration with an accuracy of 2 ns or better. Consequently, the beacon method alone can be used in the future to continuously determine and correct for GPS clock drifts in each individual event measured by AERA.

Synthesis of radio signals from extensive air showers using previously computed microscopic simulations

“…Barring these outliers by considering the 95% t.i., we can see that the timing accuracy is better than 1ns above 5 σ noise , and is good to 2ns down to a more agressive 3 σ noise trigger threshold. This is comparable to the 2ns time stamping accuracy that can be achieved with current GPS technology [25], indicating that signals synthesized with the method presented in this article can be used to develop and characterize reconstruction algorithms based on signal timing information without resulting in significant systematic errors.…”

Final results of the LOPES radio interferometer for cosmic-ray air showers

“…LOPES also pioneered many methods regarding the radio technique which have been used by other experiments, such as LOFAR, AERA, and Tunka-Rex. Examples are the continuous monitoring of the atmospheric electric field and the calibration methods used by LOPES, in particular the monitoring of the relative timing with a beacon [69,70] and the endto-end amplitude calibration using an absolutely calibrated external reference source [71][72][73]. The latter also enabled the comparison of the absolute energy scales of different airshower arrays using radio measurements [74].…”

The Radar Echo Telescope for Cosmic Rays: Pathfinder experiment for a next-generation neutrino observatory

“…The radio component of the surface system operates at 1 GS/s, allowing for precise angular reconstruction of cascades, which can then be used to test the reconstruction capabilities of the radar detector. Similar radio-based cosmic ray detectors with comparable baselines can reconstruct arrival direction with an error less than 1-2° [40][41][42][43]. At the time of writing, a set of three surface stations are taking data in a rooftop test configuration with ∼100 m baselines.…”