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

Wladimiro Leone, R. Mearns, T. Di Salvo, L. Burderi, M. Thomas, M. Trenti, F. Fiore, E. J. Marchesini, R. Campana, G. Baroni, M. Dafcikova, A. Anitra, Y. Evangelista, A. Sanna, S. Puccetti, R. Iaria, S. Barraclough, M. Ortiz del Castillo, R. Bertacin, P. Bellutti, G. Bertuccio, A. Chapman, G. Cabras, F. Ceraudo, T. Chen, M. Citossi, R. Crupi, G. Della Casa, E. Demenev, G. Dilillo, M. Feroci, F. Ficorella, M. Fiorini, N. Gao, A. Guzman, P. Hedderman, A. Hudrap, C. Labanti, G. La Rosa, P. Malcovati, J. McRobbie, F. Mele, G. Molera Calves, J. Morgan, G. Morgante, B. Negri, D. Novel, P. Nogara, A. Nuti, E. O'Brien, G. Pepponi, M. Perri, A. Picciotto, R. Piazzolla, S. Pirrotta, S. Pliego Caballero, A. Rachevski, I. Rashevskaya, A. Riggio, F. Russo, A. Santangelo, G. Sottile, C. Tenzer, Y. Tao, S. Trevisan, A. Vacchi, G. Zampa, N. Zampa, S. Xiong, S. Yi, A. Woods, S. Zhang, N. Zorzi

Abstract

The High Energy Rapid Modular Ensemble of Satellites (HERMES) instrument is a compact X/$γ$-ray spectrometer operating on board the 6U (11 kg) SpIRIT CubeSat. The payload is particularly well suited for the observation of cosmic transients such as Gamma-Ray Bursts and bright pulsars thanks to its unique broadband sensitivity from a few keV to a few MeV and the temporal resolution down to half a microsecond. We report here the detection of the $\sim$33~ms Crab pulsar double-peaked pulse profile obtained by considering the canonical Crab ephemerides as provided by the Jodrell Bank catalog. We collected approximately 5.7$\cdot$10$^4$ photons from 730~s of observations, in the 3 keV -- 2 MeV energy band, during a single operation, and achieved a 5$σ$ pulse profile significance in the 3--11.5 keV energy band with binning at the ms scale. The results demonstrate that SpIRIT/HERMES can achieve millisecond timing accuracy at high energies and, thanks to its wide field of view and broad energy band, 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 with its compact form factor.

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

Abstract

The High Energy Rapid Modular Ensemble of Satellites (HERMES) instrument is a compact X/-ray spectrometer operating on board the 6U (11 kg) SpIRIT CubeSat. The payload is particularly well suited for the observation of cosmic transients such as Gamma-Ray Bursts and bright pulsars thanks to its unique broadband sensitivity from a few keV to a few MeV and the temporal resolution down to half a microsecond. We report here the detection of the 33~ms Crab pulsar double-peaked pulse profile obtained by considering the canonical Crab ephemerides as provided by the Jodrell Bank catalog. We collected approximately 5.710 photons from 730~s of observations, in the 3 keV -- 2 MeV energy band, during a single operation, and achieved a 5 pulse profile significance in the 3--11.5 keV energy band with binning at the ms scale. The results demonstrate that SpIRIT/HERMES can achieve millisecond timing accuracy at high energies and, thanks to its wide field of view and broad energy band, 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 with its compact form factor.
Paper Structure (21 sections, 18 equations, 10 figures)

This paper contains 21 sections, 18 equations, 10 figures.

Table of Contents

  1. Introduction
  2. SpIRIT/HERMES
  3. The SpIRIT satellite
  4. The HERMES payload
  5. SpIRIT operations
  6. HERMES observations of Crab
  7. Crab absolute timing
  8. Barycentric Correction and Ephemeris Folding
  9. Energy resolved profile
  10. Period blind search
  11. Instruments comparison
  12. NuSTAR and NICER data extraction
  13. SpIRIT profile modeling
  14. Epoch folding search
  15. SpIRIT profile validation
  16. ...and 6 more sections

Figures (10)

  • Figure 1: SpIRIT and HERMES instrument FoV configuration during the Crab Pulsar/Nebula observation reported here. Top left: Orbital track of SpIRIT during data collection, with high background regions shown as shaded red, data collection began at 2025-04-01 15:36:06 UTC, and ended at 2025-04-01 15:56:06 UTC. Top right: Three-dimensional display of SpIRIT location, and HERMES instrument FoV, during the operation. Bottom: HERMES FoV occultation by Earth during the observation (for background noise estimation).
  • Figure 2: (a) Observation success statistics for the SpIRIT Crab Pulsar/Nebula observing campaign from 2024 December 11 to 2025 April 1. (b) Breakdown of the failed observation attempts by failure category.
  • Figure 3: CALibration mode file-sizes vs. elapsed observation time. Only the files in orange were downlinked from the spacecraft, forming the non-contiguous 730 s observation dataset.
  • Figure 4: SpIRIT/HERMES CRAB pulse profiles in the 3–11.5 keV band; barycentric-corrected times of arrival are folded with $P \simeq 33.84\,\mathrm{ms}$. Left: 15-channel profile with $\sim$5$\sigma$ significance. Right: 37-channel profile with $\sim$4$\sigma$ significance. The gray-shaded region indicates the peak locations and widths as inferred from the profile in \ref{['appendix:Pulsation significance maximization']}.
  • Figure 5: Blind period search with a Lomb–Scargle periodogram in the $33$–$34$ ms range: the highest peak selects the candidate period $P=33.9~\mathrm{ms}$.
  • ...and 5 more figures