CubeSats Reach the Millisecond X-Ray Domain: Crab Pulsar Timing with SpIRIT/HERMES

The High Energy Rapid Modular Ensemble of Satellites (HERMES) instrument is a compact X-/gamma-ray spectrometer operating on board the 6U (11 kg) Space Industry–Responsive–Intelligent–Thermal (SpIRIT) CubeSat. The payload is particularly well suited for the observation of cosmic transients such as gamma-ray bursts (GRBs) and bright pulsars thanks to its unique broadband sensitivity from a few keV to a few MeV and temporal resolution down to half a microsecond. We report the detection of the ∼33 ms double-peaked pulse profile of the Crab Pulsar, obtained by considering the canonical Crab ephemerides as provided by the Jodrell Bank catalog. We collected approximately 5.7 × 104 photons from 730 s of observations in the 3 keV–2 MeV energy band during a single operation, achieving a 5σ pulse-profile significance in the 3–11.5 keV energy band with millisecond-scale binning. These results demonstrate that SpIRIT/HERMES can achieve millisecond timing accuracy at high energies and, thanks to its wide field of view and broad energy coverage, has the potential to contribute to GRB monitoring in the near future. Such capabilities were previously the domain of flagship observatories, underscoring the performance of the HERMES instrument even with its compact form factor.