Periodic Reporting for period 4 - PeV-Radio (Digital Radio Detectors for Galactic PeV Particles)
Periodo di rendicontazione: 2023-08-01 al 2025-01-31
The unknown origin of the most energetic Galactic and extragalactic cosmic rays remains one of the puzzles of nature. These particles are atomic nuclei accelerated by - yet to be discovered - natural objects to energies far beyond the reach of human technology. High-energy cosmic rays are measured by special observatories through atmospheric particle cascades, called air showers. IceTop, the surface array of the IceCube Neutrino Observatory at the South Pole, is one such detector for cosmic rays. By adding radio antennas to a planned enhancement of IceTop by an array of scintillation panels, its measurement capabilities for air showers will be significantly enhanced. The improvement applies to air showers initiated by all types of cosmic particles, including cosmic-ray nuclei of different masses as well as PeV photons, which may directly reveal the sources of the cosmic rays.
In addition to IceCube, where a prototype station was installed in 2020 and subsequently upgraded, other cosmic-ray observatories may provide alternative locations for the proposed radio enhancement, such as the Pierre Auger Observatory in Argentina, which is a backup site for this project. Due to the restrictions imposed by the Covid pandemic, we have thus installed also a prototype station at the Auger site and prepared the installation of additional radio antennas at both sites. Moreover, we have used the time to further analyze data of the existing prototype station at the South Pole and developed new analysis methods for more accurate measurements of the types (mass) of primary cosmic-ray particles.
In addition to the physics goals, and important technical goal has been the experimental demonstration that radio detection of cosmic rays in the frequency band around 100-200 MHz provides a much lower detection threshold than a traditionally used band of 30-80 MHz.
In addition to IceCube, where a prototype station was installed in 2020 and subsequently upgraded, other cosmic-ray observatories may provide alternative locations for the proposed radio enhancement, such as the Pierre Auger Observatory in Argentina, which is a backup site for this project. Due to the restrictions imposed by the Covid pandemic, we have thus installed also a prototype station at the Auger site and prepared the installation of additional radio antennas at both sites. Moreover, we have used the time to further analyze data of the existing prototype station at the South Pole and developed new analysis methods for more accurate measurements of the types (mass) of primary cosmic-ray particles.
In addition to the physics goals, and important technical goal has been the experimental demonstration that radio detection of cosmic rays in the frequency band around 100-200 MHz provides a much lower detection threshold than a traditionally used band of 30-80 MHz.
After adapting the data-acquisition electronics accordingly, a prototype station including three radio antennas was installed at the South Pole in January 2020, and data has regularly been transferred by satellite. The subsequent data analysis showed that indeed we successfully measure cosmic-ray air showers with the prototype station.
However, in March 2020 the Covid pandemic and world-wide travel restrictions disrupted these plans. In particular, access to the South Pole station has been limited such that only existing instrumentation can be maintained, but no new deployments were possible for three years. As travel to the best among the backup sites for this project, the Pierre Auger Observatory in Argentina, became possible, we have completed the installation of a prototype station there end of 2022. In parallel, we prepared the hardware for further installations at both the South Pole and the Pierre Auger Observatory: several stations are completely ready to ship and several antennas have been shipped to both sites in 2024 and subsequently deployed with the help of the Pierre Auger Observatory and of IceCube collaborators at the South Pole.
Although the deployment of new instrumentation was not allowed at the South Pole through the 2022/23 season, one PhD student of the project was permitted to upgrade the existing prototype station. After successfully defending her PhD in November 2022, she was at the South Pole changing the antenna mount to the final design that she developed as one part of her PhD work on the project.
Being limited in the deployment of instrumentation, we also used the time to accelerate other aspects of the project, in particular, the preparation of software, simulations studies, the analysis of the data of the prototype station, and preparations for further data analysis. These preparations with simulation studies cover in particular important points: a) the reconstruction of the energy and position of the shower maximum of the cosmic-ray air showers, as the latter is one of the most accurate estimators for the mass of the primary particles, and b) the separation of photons against other cosmic particles using all of IceCube’s instrumentation. The latter is the work of the second out of two PhD students working on this project. He has significantly enhanced the gamma-hadron separation of IceCube to a level that provides a realistic discovery potential of PeV photon sources.
Results have been disseminated regularly at international conferences and published in the corresponding proceeding papers.
Although the Covid related delays prevented physics discoveries within the project duration, the project will still have several long-term impacts:
- the methods developed in this project will facilitate future discoveries of cosmic-ray sources
- the successful operation and data analysis of the prototype station led to the decision to include such radio antennas in the reference design of the proposed next-generation observatory IceCube-Gen2
- existing data remain available for future analyses and the antennas deployed remain operational for future data taking
Therefore, the project has been a manifold success, despite the pandemic preventing the timely achievement of the originally set goals.
However, in March 2020 the Covid pandemic and world-wide travel restrictions disrupted these plans. In particular, access to the South Pole station has been limited such that only existing instrumentation can be maintained, but no new deployments were possible for three years. As travel to the best among the backup sites for this project, the Pierre Auger Observatory in Argentina, became possible, we have completed the installation of a prototype station there end of 2022. In parallel, we prepared the hardware for further installations at both the South Pole and the Pierre Auger Observatory: several stations are completely ready to ship and several antennas have been shipped to both sites in 2024 and subsequently deployed with the help of the Pierre Auger Observatory and of IceCube collaborators at the South Pole.
Although the deployment of new instrumentation was not allowed at the South Pole through the 2022/23 season, one PhD student of the project was permitted to upgrade the existing prototype station. After successfully defending her PhD in November 2022, she was at the South Pole changing the antenna mount to the final design that she developed as one part of her PhD work on the project.
Being limited in the deployment of instrumentation, we also used the time to accelerate other aspects of the project, in particular, the preparation of software, simulations studies, the analysis of the data of the prototype station, and preparations for further data analysis. These preparations with simulation studies cover in particular important points: a) the reconstruction of the energy and position of the shower maximum of the cosmic-ray air showers, as the latter is one of the most accurate estimators for the mass of the primary particles, and b) the separation of photons against other cosmic particles using all of IceCube’s instrumentation. The latter is the work of the second out of two PhD students working on this project. He has significantly enhanced the gamma-hadron separation of IceCube to a level that provides a realistic discovery potential of PeV photon sources.
Results have been disseminated regularly at international conferences and published in the corresponding proceeding papers.
Although the Covid related delays prevented physics discoveries within the project duration, the project will still have several long-term impacts:
- the methods developed in this project will facilitate future discoveries of cosmic-ray sources
- the successful operation and data analysis of the prototype station led to the decision to include such radio antennas in the reference design of the proposed next-generation observatory IceCube-Gen2
- existing data remain available for future analyses and the antennas deployed remain operational for future data taking
Therefore, the project has been a manifold success, despite the pandemic preventing the timely achievement of the originally set goals.
We use the SKALA v2 antenna type for our project, which was originally developed for the Square Kilometer Array (SKA). This antenna type combines a wide sky coverage with a broad frequency band, which includes our measurement band from below 100 MHz to 350 MHz. With the prototype station we confirmed that we can lower the cosmic-ray detection threshold compared to the traditional 30-80 MHz band used by prior experiments.
In addition, we have been working to exploit the IceCube data already available to the extent possible for the first science goal of searching for PeV photons, improving analysis methods regarding the angular resolution, threshold, and gamma-hadron separation. A PhD student working on the project has achieved and order-of-magnitude improvement of the gamma-hadron separation. Generally, the enhanced mass separation of cosmic rays as well as the detection of photons have the potential to solve the long-standing puzzle of the origin of the highest energy cosmic rays from our own Galaxy. Hence, the analysis techniques developed will contribute to this scientific quest despite the Covid imposed delays on the instrumentation.
Regarding the analysis of the prototype station at the South Pole, we could also demonstrate the measurement of the position of the shower maximum with the prototype station for several cosmic-ray events. This came unexpected, as many scientists in the field believed that at least 5 antennas are required for a reasonable resolution on the shower maximum, and the prototype station has only 3 antennas. Nonetheless, through further improvements of the state-of-the-art template fitting analysis technique, we could demonstrate that for a subset of the measured events already three antennas provide a competitive resolution.
Finally, due to the convincing results of the prototype station, complemented with simulation studies, the IceCube-Gen2 collaboration has decided to adopt the station design for the planned IceCube-Gen2 Surface Array. This is described in part II of the Technical Design Report. Therefore, this ERC project will have a lasting impact much beyond its duration, as IceCube-Gen2 is proposed to be deployed in the 2030's and to operate for at least a decade.
In addition, we have been working to exploit the IceCube data already available to the extent possible for the first science goal of searching for PeV photons, improving analysis methods regarding the angular resolution, threshold, and gamma-hadron separation. A PhD student working on the project has achieved and order-of-magnitude improvement of the gamma-hadron separation. Generally, the enhanced mass separation of cosmic rays as well as the detection of photons have the potential to solve the long-standing puzzle of the origin of the highest energy cosmic rays from our own Galaxy. Hence, the analysis techniques developed will contribute to this scientific quest despite the Covid imposed delays on the instrumentation.
Regarding the analysis of the prototype station at the South Pole, we could also demonstrate the measurement of the position of the shower maximum with the prototype station for several cosmic-ray events. This came unexpected, as many scientists in the field believed that at least 5 antennas are required for a reasonable resolution on the shower maximum, and the prototype station has only 3 antennas. Nonetheless, through further improvements of the state-of-the-art template fitting analysis technique, we could demonstrate that for a subset of the measured events already three antennas provide a competitive resolution.
Finally, due to the convincing results of the prototype station, complemented with simulation studies, the IceCube-Gen2 collaboration has decided to adopt the station design for the planned IceCube-Gen2 Surface Array. This is described in part II of the Technical Design Report. Therefore, this ERC project will have a lasting impact much beyond its duration, as IceCube-Gen2 is proposed to be deployed in the 2030's and to operate for at least a decade.