Resolve the origin of the Resolve-array redshift shift

Determine whether the monotonic redshift increase observed when excluding Resolve pixels 31 and 32 is caused by a genuine velocity gradient across the Abell 1413 intracluster medium or by statistical noise.

Background

The authors compare spectral fits using the full Resolve array and configurations that exclude pixels 31, 32, or both. The fitted redshift increases monotonically as these pixels are removed, corresponding to a 5 km s−1 shift. This could indicate that the excluded pixels sample a slightly different part of the intracluster-medium velocity field.

However, the shift is small relative to the statistical uncertainty, and the authors explicitly state that the available data cannot determine whether it is physical or statistical. Although the effect is negligible for the reported bulk velocity, its underlying cause remains unresolved.

References

Because it is monotonic rather than random, it may reflect a mild velocity gradient across the array, with pixels~31 and~32 sampling a slightly different part of the velocity field; it is equally consistent with statistical noise, and the present data cannot distinguish between the two.

— Weak cool core, weak turbulence: XRISM, XMM-Newton and Chandra spectroscopy of the core of Abell 1413  (2609.08778 - Gormez et al., 8 Sep 2026) in Appendix, Section “Point-source contamination of the Resolve spectrum” (Section \ref{app:pointsources})