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Solar Flare Hard X-ray Polarimetry with the CUbesat Solar Polarimeter (CUSP) mission

Nicolas De Angelis, Andrea Alimenti, Davide Albanesi, Ilaria Baffo, Daniele Brienza, Riccardo Campana, Valerio Campamaggiore, Mauro Centrone, Enrico Costa, Giovanni Cucinella, Andrea Curatolo, Giovanni De Cesare, Giulia de Iulis, Ettore Del Monte, Andrea Del Re, Sergio Di Cosimo, Simone Di Filippo, Giuseppe Di Persio, Immacolata Donnarumma, Sergio Fabiani, Pierluigi Fanelli, Nicolas Gagliardi, Abhay Kumar, Alessandro Lacerenza, Paolo Leonetti, Pasqualino Loffredo, Giovanni Lombardi, Matteo Mergè, Gabriele Minervini, Dario Modenini, Fabio Muleri, Andrea Negri, Daniele Pecorella, Massimo Perelli, Alice Ponti, Paolo Romano, Alda Rubini, Emanuele Scalise, Enrico Silva, Paolo Soffitta, Paolo Tortora, Alessandro Turchi, Valerio Vagelli, Emanuele Zaccagnino, Alessandro Zambardi, Costantino Zazza

TL;DR

Hard X-ray polarimetry of solar flares can reveal the geometry of magnetic reconnection and the beaming of accelerated electrons, a domain with historically limited data. The paper describes the CUSP mission, a 6U CubeSat carrying a dual-phase Compton polarimeter sensitive to 25–100 keV, consisting of 64 plastic scintillator bars (scatterers) and 32 GAGG:Ce crystals (absorbers) read out by MAPMTs and APDs, respectively, with a tungsten collimator and specialized electronics. Geant4 simulations and laboratory prototypes indicate MDPs of a few percent in short integrations, and the design supports potential twin-satellite deployments to improve solar coverage. By delivering time-resolved polarization measurements, CUSP aims to constrain the location and physics of particle acceleration in flares and inform space-weather forecasting.

Abstract

The CUbesat Solar Polarimeter (CUSP) project is a CubeSat mission planned for a launch in low-Earth orbit and aimed to measure the linear polarization of solar flares in the hard X-ray band by means of a Compton scattering polarimeter. CUSP will allow us to study the magnetic reconnection and particle acceleration in the flaring magnetic structures of our star. CUSP is a project in the framework of the Alcor Program of the Italian Space Agency aimed at developing new CubeSat missions. It is undergoing a 12-month Phase B that started in December 2024. The Compton polarimeter on board CUSP is composed of two acquisition chains based on plastic scintillators read out by Multi-Anode PhotoMultiplier Tubes for the scatterer part and GAGG crystals coupled to Avalanche PhotoDiodes for the absorbers. An event coincident between the two readout schemes will lead to a measurement of the incoming X-ray's azimuthal scattering angle, linked to the polarization of the solar flare in a statistical manner. The current status of the CUSP mission design, mission analysis, and payload scientific performance will be reported. The latter will be discussed based on preliminary laboratory results obtained in parallel with Geant4 simulations.

Solar Flare Hard X-ray Polarimetry with the CUbesat Solar Polarimeter (CUSP) mission

TL;DR

Hard X-ray polarimetry of solar flares can reveal the geometry of magnetic reconnection and the beaming of accelerated electrons, a domain with historically limited data. The paper describes the CUSP mission, a 6U CubeSat carrying a dual-phase Compton polarimeter sensitive to 25–100 keV, consisting of 64 plastic scintillator bars (scatterers) and 32 GAGG:Ce crystals (absorbers) read out by MAPMTs and APDs, respectively, with a tungsten collimator and specialized electronics. Geant4 simulations and laboratory prototypes indicate MDPs of a few percent in short integrations, and the design supports potential twin-satellite deployments to improve solar coverage. By delivering time-resolved polarization measurements, CUSP aims to constrain the location and physics of particle acceleration in flares and inform space-weather forecasting.

Abstract

The CUbesat Solar Polarimeter (CUSP) project is a CubeSat mission planned for a launch in low-Earth orbit and aimed to measure the linear polarization of solar flares in the hard X-ray band by means of a Compton scattering polarimeter. CUSP will allow us to study the magnetic reconnection and particle acceleration in the flaring magnetic structures of our star. CUSP is a project in the framework of the Alcor Program of the Italian Space Agency aimed at developing new CubeSat missions. It is undergoing a 12-month Phase B that started in December 2024. The Compton polarimeter on board CUSP is composed of two acquisition chains based on plastic scintillators read out by Multi-Anode PhotoMultiplier Tubes for the scatterer part and GAGG crystals coupled to Avalanche PhotoDiodes for the absorbers. An event coincident between the two readout schemes will lead to a measurement of the incoming X-ray's azimuthal scattering angle, linked to the polarization of the solar flare in a statistical manner. The current status of the CUSP mission design, mission analysis, and payload scientific performance will be reported. The latter will be discussed based on preliminary laboratory results obtained in parallel with Geant4 simulations.

Paper Structure

This paper contains 5 sections, 1 equation, 2 figures, 2 tables.

Table of Contents

  1. Motivation for Solar Flare Polarimetry
  2. The CUbesat Solar Polarimeter (CUSP)
  3. The CUSP mission
  4. CUSP's Hard X-ray Polarimeter
  5. Conclusions and Outlook

Figures (2)

  • Figure 1: Detection principle of a dual-phase Compton polarimeter. Left: Top view of CUSP with 64 scatters in blue surrounded by 32 absorbers in red. The dashed white line shows an event for which the incoming photon is scattered and then absorbed in two different channels (adapted from CUSP_animation, with permissions). The azimuthal scattering direction is given by the angle $\phi$. Right: Azimuthal scattering angle distribution, a.k.a. modulation curve, built from a non-polarized incoming flux (adapted from CUSP_animation, with permissions).
  • Figure 2: CAD exploded view of CUSP's hard X-ray polarimeter