Determine the distance to EP J223759.5+531421

Determine the distance to the magnetar EP J223759.5+531421 in order to constrain the physical sizes of its emitting regions and the interpretation of its spectral components.

Background

The paper adopts a distance of 3.3 kpc when converting blackbody normalizations into emission radii, but this value is motivated by the Galactic hydrogen-density profile and the likely association of the source with the Perseus spiral arm rather than by a direct distance measurement. The authors note that the measured hydrogen column density favors a distance below approximately 5 kpc, leaving the source distance unresolved and consequently making the inferred emitting radii distance-dependent.

References

The distance $D$ of EP J223759.5+531421\ is still unknown but the value of $N_\mathrm{H}$ argues in favor of $D\lesssim 5\,\mathrm{kpc}$ and its position on the sky makes an association with the Perseus spiral arm likely.

— IXPE observation of the new magnetar source EP J223759.5+531421  (2609.25958 - Taverna et al., 22 Sep 2026) in Section 3, footnote to the two-blackbody spectral-analysis paragraph

The reconstructed gas distribution thus favours an association with the Perseus arm, although an inter-arm location along the same line of sight cannot be ruled out.

— Einstein Probe discovery of the magnetar EP J223759.5+531421  (2609.25990 - Rea et al., 22 Sep 2026) in Section 3.6, “Distance estimate”; Discussion, paragraph beginning “The Galactic location of”