Presence of the (l,m,n) = (4,4,0) quasi-normal mode in GW250114

Ascertain whether the Kerr quasi-normal mode with angular indices (l, m, n) = (4, 4, 0) (the 440 mode) is present in the GW250114 ringdown signal.

Background

The authors use a parameterized inspiral–merger–ringdown model (pSEOBNR) to constrain deviations in quasi-normal-mode frequencies and damping times across the full waveform. Because this framework enforces continuity and does not allow mode amplitudes to vanish, it yields constraints consistent with GR but cannot alone establish whether a subdominant mode is present. Specifically for the (4,4) fundamental mode, they obtain frequency constraints but state they cannot by themselves determine its presence, motivating further analyses that isolate ringdown content.