About half of the baryons in the local universe are thought to reside in the so-called warm-hot intergalactic medium (WHIM) at temperatures of 0.1-10 MK. Thermal soft excess emission in the spectrum of some cluster outskirts that contains O Ⅶ and/or O Ⅷ emission lines is regarded as evidence of the WHIM, although the origin of the lines is controversial due to strong Galactic and solar system foreground emission. We observed the Coma-11 field, where the most prominent thermal soft excess has been reported, with Suzaku XIS in order to clarify the origin of the excess. We did not confirm O Ⅶ or O Ⅷ excess emission. The O Ⅶ and O Ⅷ intensity in Coma-11 is more than 5 σ below that reported before, and we obtained 2 σ upper limits of 2.8 and 2.9 photons cm~(-2) s~(-1) sr~(-1) for O Ⅶ and O Ⅷ, respectively. The intensities are consistent with those in another field (Coma-7) that we measured, and with other measurements in the Coma outskirts (Coma-7 and X Com field with XMM-Newton). We did not confirm the spatial variation within Coma outskirts. The strong oxygen emission lines previously reported are likely due to solar wind charge exchange.
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