Detecting the effect of non-thermal sources on the warm-hot Galactic halo

We report the first detection of non-thermal broadening of OVII lines in the warm-hot ≈ 10⁶ K circumgalactic medium (CGM) of the Milky Way. We use z=0 absorption of OVII Kα, OVII Kβ, and OVIII Kα lines in archival grating data of $b>$15^∘ quasar sightlines from $Chandra$ and $XMM$-$Newton$. Non-thermal line broadening is evident in two-third of the sightlines considered, and on average is constrained at 4.6σ significance. Non-thermal line broadening dominates over thermal broadening. We extensively test whether the appearance of non-thermal line broadening could instead be because of multiple thermally broadened velocity components and robustly rule it out. Non-thermal line broadening is more evident toward sightlines at lower galactic latitude indicating the Galactic disk origin of the nonthermal sources. There is weak/no correlation between non-thermal line broadening and the angular separation of sightlines from the Galactic center, indicating that the nuclear region might not be a major source of non-thermal factors.