Observation of a propagating slow magnetoacoustic wave in a coronal plasma fan with SDO/AIA and SolO/EUI

Simultaneous observations of a propagating disturbance of EUV intensity, with SDO/AIA at 171 & Aring; and SolO/EUI-HRIEUV at 174 & Aring;, are investigated. The disturbance moves outwards along a plasma fan structure in active region AR 12941 on February 7th 2022, at 12:45-14:15 UT. The spacecraft line-of-sight separation is 19 degrees. The variation of the EUV intensity resembles an almost harmonic wave with an oscillation period of 2.7(-0.2)(+0.1) and 2.6(-0.1)(+0.1) min for AIA and HRIEUV, respectively. Over 30 oscillation cycles are detected. The wave originated at the footpoint of the fan, anchored in a sunspot. The projected phase speeds are 60.5 +/- 5.2 and 74.4 +/- 6.2 km s(-1) in the AIA and HRIEUV data, respectively, determined by the cross-correlation technique. The observed parameters of the propagating EUV disturbance suggest its interpretation as a slow magnetoacoustic wave. Observations with AIA show that the wave decays with height, with a calculated e-folding length of 6.9(-0.8)(+1.3) Mm. In contrast, in the HRIEUV data, the propagating EUV disturbance is also seen much higher, with the e-folding length of 12.8(-1.7)(+1.1) Mm. This observation demonstrates, for the first time, that the apparent spatial damping of propagating slow waves depends on the observational instrument. Moreover, our work shows that the study of slow waves can be advanced with the use of HRIEUV, and multiple instruments with non-parallel lines of sight.