Speaker
Description
LISA will be the first space-based gravitational wave observatory sensitive to the unexplored frequency band of 0.1 mHz – 1 Hz. It will consist of three identical spacecraft (SC) 2.5 million km away from each other. Each SC will be equipped with lasers and free-falling test masses (TMs). When gravitational waves reach the SC, they will be detected by measuring variations in the distance between TMs located in different SC. However, background radiation interacting with the SCs may charge the TMs, limiting LISA sensitivity, especially < 1mHz. Therefore, monitoring the background radiation flux is essential to understand the charging nature of the TMs and evaluate its associated systematic uncertainties.
Protons with E>100 MeV and heavier ions will contribute to TM charging. We have designed a Radiation Monitor (RM) designed to detect protons and alpha particles above ~70 MeV and ~600 MeV, respectively, allowing the measurement of cosmic-ray flux variations with ~1% statistical error in ~1 hour. The RM will have at least 4 energy channels between 100 MeV and 1 GeV for spectrum reconstruction. Together with the LISA high-precision magnetometers, the RM will provide a unique measurement of the high-energy component of solar energetic particles in an energy range that is not commonly accessed by most solar particle detectors. We selected a sample of SEPs with activity at high energies and studied the expected response of the RM. In the contribution we will show that the RM might also be sensitive to extremely bright gamma-ray bursts. In this scenario, with three identical detectors 8 s away from each other the angular resolution would be outstanding.
We have built a demonstrator of the RM and characterized it in the laboratory, through a dedicated proton beam and Monte Carlo simulations. The RM consists of a telescopic arrangement of four plastic scintillators and three W absorbers. The scintillators are coupled to silicon photomultipliers and their readout is performed by the BETA ASIC, which can amplify, shape and digitize the signals of up to 64 channels with low power consumption. This prototype will fly with other LISA subsystems (magnetometers, temperature sensors) in a small satellite in 2026. The main goals will be the demonstration of the technology developed for LISA and the characterization of the Birkeland currents near the Earth poles. I will describe the design of the RM, the results of the characterization and its expected on-flight performance and detection capabilities.
| Collaboration(s) | LISA |
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