Calibration and Performance of the Full-Disk Vector MagnetoGraph (FMG) on Board the Advanced Space-Based Solar Observatory (ASO-S)

We present the ground calibration and on-orbit performance of the Full-disk vector MagnetoGraph (FMG) payload on board the Advanced Space-Based Solar Observatory (ASO-S), which is China’s first spaceborne magnetograph. FMG has the ability to acquire the full-disk Stokes I, Q/I, U/I, and V/I maps with a spatial resolution of about 1.5 arcsec. The Lyot filter for the flight model has a full width at half maximum of 0.01 nm. Using two calibration lenses, we measure the non-uniform wavelength drift across the entire field of view, with a maximum value of 0.003 nm. The on-orbit polarization sensitivity is approximately 0.00039 and 0.0009 for the deep integration and routine modes, corresponding to a cadence of 18 and 2 minutes, respectively. The corresponding sensitivity of the longitudinal magnetic field is 8.5 G and 20 G with the current linear calibration coefficient of 21,913. Since 1 April 2023, FMG has released Level 2 filtergram and longitudinal magnetic field data products for active regions. Furthermore, line-of-sight Carrington synoptic magnetograms spanning a 27-day solar rotation can be generated, which have been released to the public since February 2024. The longitudinal magnetic field obtained by FMG is consistent with that of the Helioseismic and Magnetic Imager on board the Solar Dynamic Observatory and the Solar Magnetism and Activity Telescope at Huairou Solar Observing Station for the regions without magnetic saturation.