  We report on the detection of a previously unknown extended low-density
nebula of very high temperature and excitation, TR001507.7-391206, located
above the midplane of NGC55. The nebular emission line spectrum, in which HeII
is present, is consistent with photoionization by about 3 very hot massive O3
or WR-type stars. There are no indications for shock ionization. The faint blue
optical continuum and XMM-Newton EPIC-pn and OM-data also support our
assumption that this nebula is not a supernova remnant. Galactic nebulae
harboring massive Wolf-Rayet (WR) stars may be appropriate examples, in
particular the highly ionized nebula G2.4+1.4 around WR 102 (aka Sk4 or
LSS4368). The relatively large diameter of the inhomogeneously expanding nebula
in NGC55 of about 58pc, compared to 11pc of G2.4+1.4, would also be consistent
with the number of ionizing stars.
