Calibrating the cosmic-ray energy scale of the Pierre Auger Observatory using radio detection of extensive air showers in AERA
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Comisión Nacional de Energía Atómica; Argentina. Gerencia de Área Académica. Gerencia Instituto de Tecnología "Jorge Sabato"
Universidad Nacional San Martin. Instituto de Tecnología "Jorge Sabato"; Argentina
Department of Physics of the Karlsruhe Institute of Technology (KIT); Alemania
Universidad Nacional San Martin. Instituto de Tecnología "Jorge Sabato"; Argentina
Department of Physics of the Karlsruhe Institute of Technology (KIT); Alemania
Resumen
El Observatorio Pierre Auger es la mayor instalación de detección de rayos cósmicos de ultra alta energía. Mediante observaciones multihíbridas de cascadas atmosféricas extensas, mide propiedades clave de las partículas cósmicas. Una técnica de detección cuya importancia para la comunidad ha crecido significativamente en los últimos años, es la medición de las señales de radio coherentes liberadas en las cascadas atmosféricas. En el Observatorio Auger durante más de diez años la detección de radio se ha llevado a cabo en una pequeña parte del observatorio con el Auger Engineering Radio Array (AERA). La experiencia y los éxitos realizados con AERA dieron lugar a la instalación reciente del nuevo Radio Detector (RD), que está en marcha para ampliar los estudios realizados con AERA y mejorar la sensibilidad y los resultados de la física del Observatorio Pierre Auger en general. Una tarea particular que puede realizarse con los detectores de radio es determinar la escala de energía absoluta de los rayos cósmicos. Proporcionar una escala de energía precisa es crucial para la interpretación de casi todos los resultados sobre las propiedades de los rayos cósmicos que pueden obtenerse con el Observatorio Auger. Reunimos varios ingredientes de las mediciones obtenidas con la calibración de energía de AERA para realizar una calibración cruzada con la calibración obtenida mediante el detector de fluorescencia (FD) del observatorio Pierre Auger. Como primer ingrediente, hacemos uso de estadísticas sin precedentes de mediciones híbridas con el arreglo de detectores de superficie densa (SD-750) y AERA. Los datos de AERA se limpian para los periodos afectados por fuertes campos atmosféricos en tormentas eléctricas utilizando los molinos de campo eléctrico existentes. Para poder realizar en el futuro un análisis de seguimiento de la escala de radioenergía con el RD, desplegamos cinco nuevas estaciones remotas con molinos de campo eléctrico repartidas por todo el Observatorio Pierre Auger. Las estaciones están diseñadas para proporcionar automáticamente una calibración absoluta de sus medidas de campo eléctrico con una precisión del 6,5%. Otros ingredientes para el análisis a escala energética con AERA incluyen una reconstrucción de radio apropiada y una calibración precisa de AERA utilizando la emisión difusa galáctica. La calibración galáctica desempeña un papel clave en la escala de energía de radio. Para comprender su precisión, realizamos un estudio dedicado sobre modelos del cielo galáctico en radio encontrando una estimación de la incertidumbre sistemática global del 7,2% en la escala de energía de rayos cósmicos, la cual que se reduce al 5,9% en el caso de los detectores de radio del Observatorio Auger. Con todos los ingredientes recogidos, seleccionamos alrededor de 600 eventos híbridos de lluvia de aire (SD 750 – AERA) de alta calidad que simulamos en CORSIKA y CoREAS con su energía estimada en la escala de energía FD. Estos eventos tienen energías entre 3×1017 eV y 4×1018 eV y ángulo cenital de hasta 55◦. Mediante la comparación de los datos con la simulación de los estimadores de energía de radio, descubrimos que la escala de energía de radio es un 12% más alta que la escala de energía FD. Discutimos ampliamente las incertidumbres sistemáticas, las cuales son del orden de la diferencia entre las escalas de energía. Este resultado constituye una importante verificación independiente de la escala de energía del Observatorio Pierre Auger. En perspectiva, las escalas de energía FD y radio podría combinarse. Una validación y extensión del análisis presentado a eventos inclinados y a las energías más altas se realizará con el RD.
The Pierre Auger Observatory is the largest facility for the detection of ultra-high energetic cosmic rays. With multi-hybrid observations of extensive air showers it measures key properties of the cosmic particles. One detection technique whose relevance to the community has grown significantly in the past years, is the measurement of coherent radio signals release in air showers. At the Auger Observatory, radio detection has been taken on in a small part of the observatory with the Auger Engineering Radio Array (AERA) for over ten years. The experiences and successes made with AERA resulted in the recently installed new Radio Detector (RD) that is on to expand on studies made with AERA and enhance the sensitivity and physics results of the Pierre Auger Observatory in general. One particular task that can be done with radio detectors is determining the absolute energy scale of cosmic rays. Providing an accurate energy scale is crucial to the interpretation of almost all results about the properties of cosmic rays that can be obtained with the Auger Observatory. We bring together several ingredients for calibrated energy measurements of air showers with AERA to perform a cross calibration of its energy scale with the established energy scale of the Pierre Auger Observatory from the fluorescence detector (FD). As the first ingredient, we make use of unprecedented statistics of hybrid measurements with the dense Surface detector array (SD-750) and AERA. The AERA data are cleaned for periods affected by strong atmospheric fields in thunderstorms using existing electric field mills. To be able to conduct a follow-up analysis of the radio energy scale with the RD in the future, we deployed five new remote stations with electric field mills spread across the Pierre Auger Observatory. The stations are designed to automatically provide an absolute calibration of their electric-field measurements with an accuracy of 6.5%. Further ingredients for the energy-scale analysis with AERA include a well developed radio reconstruction and an accurate calibration of AERA using the diffuse Galactic emission. The Galactic calibration plays a key role in the radio energy scale. To understand its accuracy, we perform a dedicated study on models of the Galactic radio sky finding a global systematic uncertainty estimate of 7.2% on the cosmic-ray energy scale that reduces to 5.9% in the case of the radio detectors at the Auger Observatory. With all ingredients collected, we select around 600 hybrid air-shower events (SD-750 – AERA) of high quality that we simulate in CORSIKA and CoREAS with their energy estimated on the FD energy scale. These events have energies from 3×1017 eV to 4×1018 eV and zenith angles up to 55◦. By data-to-simulation comparison of the radio energy estimators, we find that the radio energy scale is set 12% higher than the FD energy scale. We discuss the systematic uncertainties extensively, which currently are of the order of the difference between the energy scales. This result constitutes an important independent cross-check of the energy scale of the Pierre Auger Observatory. Perspectively, the FD and radio energy scale could be combined. A validation and extension of the presented analysis to inclined events and to the highest energies will be done with the RD.
The Pierre Auger Observatory is the largest facility for the detection of ultra-high energetic cosmic rays. With multi-hybrid observations of extensive air showers it measures key properties of the cosmic particles. One detection technique whose relevance to the community has grown significantly in the past years, is the measurement of coherent radio signals release in air showers. At the Auger Observatory, radio detection has been taken on in a small part of the observatory with the Auger Engineering Radio Array (AERA) for over ten years. The experiences and successes made with AERA resulted in the recently installed new Radio Detector (RD) that is on to expand on studies made with AERA and enhance the sensitivity and physics results of the Pierre Auger Observatory in general. One particular task that can be done with radio detectors is determining the absolute energy scale of cosmic rays. Providing an accurate energy scale is crucial to the interpretation of almost all results about the properties of cosmic rays that can be obtained with the Auger Observatory. We bring together several ingredients for calibrated energy measurements of air showers with AERA to perform a cross calibration of its energy scale with the established energy scale of the Pierre Auger Observatory from the fluorescence detector (FD). As the first ingredient, we make use of unprecedented statistics of hybrid measurements with the dense Surface detector array (SD-750) and AERA. The AERA data are cleaned for periods affected by strong atmospheric fields in thunderstorms using existing electric field mills. To be able to conduct a follow-up analysis of the radio energy scale with the RD in the future, we deployed five new remote stations with electric field mills spread across the Pierre Auger Observatory. The stations are designed to automatically provide an absolute calibration of their electric-field measurements with an accuracy of 6.5%. Further ingredients for the energy-scale analysis with AERA include a well developed radio reconstruction and an accurate calibration of AERA using the diffuse Galactic emission. The Galactic calibration plays a key role in the radio energy scale. To understand its accuracy, we perform a dedicated study on models of the Galactic radio sky finding a global systematic uncertainty estimate of 7.2% on the cosmic-ray energy scale that reduces to 5.9% in the case of the radio detectors at the Auger Observatory. With all ingredients collected, we select around 600 hybrid air-shower events (SD-750 – AERA) of high quality that we simulate in CORSIKA and CoREAS with their energy estimated on the FD energy scale. These events have energies from 3×1017 eV to 4×1018 eV and zenith angles up to 55◦. By data-to-simulation comparison of the radio energy estimators, we find that the radio energy scale is set 12% higher than the FD energy scale. We discuss the systematic uncertainties extensively, which currently are of the order of the difference between the energy scales. This result constitutes an important independent cross-check of the energy scale of the Pierre Auger Observatory. Perspectively, the FD and radio energy scale could be combined. A validation and extension of the presented analysis to inclined events and to the highest energies will be done with the RD.