High Energy Cosmic Particles

Radio-quiet cosmic ray detector deployed at the MRO

The field prototype of a particle-detector system for the SKA, described in the previous edition of this newsletter, has been deployed at the Murchison Radio-astronomy Observatory, the planned site of SKA-LOW. The detector module, developed at the Jodrell Bank Centre for Astrophysics at the University of Manchester, is sited between the Murchison Widefield Array (MWA) and the Aperture Array Verification System, respectively a precursor and a prototype for SKA-LOW. An array of these detectors will ultimately enable SKA-LOW to carry out precision studies of cosmic rays interacting in the atmosphere above the telescope.

Both the detector module and support equipment (power supply and data acquisition units) passed extensive testing for radio-frequency emissions by staff at ICRAR/Curtin University and CSIRO Astronomy & Space Science. Minimal emissions were detected from the support equipment, which will go through further revisions, with no detectable emission from the module itself.

While this single detector cannot be used to identify high-energy particle cascades, it routinely detects the passage of individual energetic muons, which are primarily produced by low-energy cosmic ray interactions in the atmosphere. The passage of these particles through the plastic scintillator block inside the detector produces a burst of light which is detectable to all four silicon photomultipliers (SiPMs). Analogue delays are used so that the four SiPM pulses appear as pulse trains.

Over the coming year, the system will be operated as an MWA External Instrument, and undergo various stability and verification tests, using the muon signature as a calibrator source.

This deployment was carried out with major assistance from ICRAR/Curtin University and the Murchison Widefield Array. Further preparatory work was carried out by staff at CSIRO Astronomy & Space Science.

Internal systems of the particle detector, being prepared for deployment. The transparent panel scintillates when hit by a high-energy particle, producing a pulse of light that is detected by the four photodetectors on circuit boards along its edges. These then pass through the coiled, black delay lines before they are combined into a single channel, exiting the detector along a fibre passing through the brass pipe on the far side. (Image credit: Alex Williamson)


The deployment team with the detector in the field. The pallets raise it to avoid the risk of flooding damage. Top row: Don Hutton, Alexander Williamson, Oakley Criddle, Justin Bray. Bottom: David Emrich, Andrew McPhail (Image credit: Nipanjana Patra)

A pulse train from all four silicon photomultipliers indicating the passage of a muon through the detector, sampled at 1.024 GHz. The DAQ and readout is now fully integrated into the MRO control building and accessible remotely via ssh. (Image credit: Alex Williamson).

ARENA 2018

The 8th international workshop on Acoustic and Radio EeV Neutrino Detection Activities (ARENA 2018)was held in June in Catania, Italy. The detection of cosmic rays as well as neutrinos is now a major focus of the bi-annual workshop series, with 33 contributions on the radio-detection of cosmic rays interacting the in Earth’s atmosphere. Highlights included recent results from LOFAR, Tunka-Rex, and AERA, and cosmic ray measurements from the ARIANNA and ANITA neutrino experiments in Antarctic. In particular, plans for new radio detection systems were presented, including an array above the IceCube neutrino telescope; a doubling of the size of LORA, the particle detector array used to trigger LOFAR; an expansion of the Askaryan Radio Array (ARA); and the status of the next stage of GRAND, the Giant Radio Array for Neutrino Detection, to be constructed in Xinjiang Province, China.

Cosmic Ray Detection at Owens Valley Radio Observatory

The Owens Valley Long-Wavelength Array (OVRO-LWA) in California recently tested whether cosmic ray detection without a particle detector array is feasible. In a dedicated campaign, Ryan Monroe developed a self-trigger algorithm that recorded a total of 473k impulsive events within 40 hours of observation. Profiting from direct access to raw data and few computational restrictions, the team was able to beat-down RF from power-lines, AC units, nearby cites, and airplanes to conclusively identify 10 cosmic ray events. The methods enabling cosmic ray detection in radio-only data are detailed in a paper submitted to Nuclear Instruments and Methods A.

The appendices of this article contain valuable lessons for any future instrument attempting radio-only triggering. Now that the RF backgrounds and cosmic ray signatures are well-established, the ‘holy grail’ of a fully efficient radio-only trigger may be within reach, although particle detector data is still valuable when comparing the leptonic and hadronic components of cosmic ray cascades. This powerful radio-only trigger is needed to keep data-rates low and event purity high for large dispersed radio arrays for the detection of neutrinos above 1017 eV, as is the target of experiments such as GRAND, ARIANNA, and ARA.

Cosmic-ray-induced air shower as measured with the OVRO-LWA. The pulse power is encoded in the size of the circles. Details in R. Monroe et al., submitted to Nuclear Instruments and Methods A.


Report provided by Justin Bray, Jodrell Bank Centre for Astrophysics