A hot bubble at the centre of M81
  Context. Messier 81 has the nearest active nucleus with broad H$\alpha$
emission. A detailed study of this galaxy's centre is important for
understanding the innermost structure of the AGN phenomenon.
  Aims. Our goal is to seek previously undetected structures using additional
techniques to reanalyse a data cube obtained with the GMOS-IFU installed on the
Gemini North telescope (Schnorr M\"uller et al. 2011).
  Method. We analysed the data cube using techniques of noise reduction,
spatial deconvolution, starlight subtraction, PCA tomography, and comparison
with HST images.
  Results. We identified a hot bubble with T $>$ 43500 K that is associated
with strong emission of [N II]$\lambda$5755\AA\ and a high [O
I]$\lambda$6300/H$\alpha$ ratio; the bubble displays a bluish continuum,
surrounded by a thin shell of H$\alpha$ + [N II] emission. We also reinterpret
the outflow found by Schnorr M\"uller et al. (2011) showing that the
blueshifted cone nearly coincides with the radio jet, as expected.
  Conclusions. We interpret the hot bubble as having been caused by post
starburst events that left one or more clusters of young stars, similar to the
ones found at the centre of the Milky Way, such as the Arches and the IRS 16
clusters. Shocked structures from combined young stellar winds or supernova
remnants are probably the cause of this hot gas and the low ionization
emission.
