Determine whether aligned rotators are common among accreting millisecond pulsars

Determine whether accreting millisecond pulsars commonly possess emitting spots closely aligned with their spin axes.

Background

IXPE observations of SAX J1808.4–3658 and SRGA J144459.2–604207 found low linear X-ray polarisation at the 2%–3% level without detectable phase-resolved variability. The authors interpret this as evidence that the emitting spots may be closely aligned with the neutron-star spin axes.

Because only two accreting millisecond pulsars have so far been observed polarimetrically, it remains unresolved whether this geometry is characteristic of the broader accreting millisecond-pulsar population. Additional IXPE campaigns are needed to test its prevalence.

References

Future IXPE campaigns will determine whether aligned rotators are a common feature among AMSPs.

— Polarised X-ray emission from the accreting millisecond pulsar SAX J1808.4-3658 during an X-ray outburst and a type-I X-ray burst  (2610.09477 - Papitto et al., 7 Oct 2026) in Section 3, Discussion and conclusions