  Context: The geometry of the circumstellar envelopes (CSE) surrounding Be
stars is still uncertain, although it is often assumed that they are formed by
a disk around the stellar equator and a hot polar wind. Achernar (Alpha Eri) is
the nearest Be star, and we recently detected a CSE using near-IR
interferometry. Aims: Our initial goal was to constrain the geometry and flux
contribution of the CSE of Achernar at distances of a few tens of AU from the
star, in the thermal IR domain to complement our near-IR interferometric
observations. Methods: We obtained diffraction-limited images of Achernar in
the thermal infrared using VISIR at the VLT. In order to freeze the turbulence,
we used the BURST mode of this instrument. Results: The images obtained in the
PAH1 band show a point-like source located 0.280" north-west of Achernar
(projected linear separation of 12.3 AU). Its emission is 1.8 % of the flux of
Achernar in this band, but is not detected in the PAH2, SiC and NeII bands. We
also provide new thermal IR photometry of Achernar in four bands. Conclusions:
Being aligned with the expected azimuth of the equatorial plane of Achernar,
the detected source could be a main sequence stellar companion. In this case,
it apparent brightness would correspond to an A7V spectral type.
