  The presence of luminous hot X-ray coronae in the dark matter halos of
massive spiral galaxies is a basic prediction of galaxy formation models.
However, observational evidence for such coronae is very scarce, with the first
few examples having only been detected recently. In this paper, we study the
large-scale diffuse X-ray emission associated with the massive spiral galaxy
NGC266. Using ROSAT and Chandra X-ray observations we argue that the diffuse
emission extends to at least ~70 kpc, whereas the bulk of the stellar light is
confined to within ~25 kpc. Based on X-ray hardness ratios, we find that most
of the diffuse emission is released at energies <1.2 keV, which indicates that
this emission originates from hot X-ray gas. Adopting a realistic gas
temperature and metallicity, we derive that in the (0.05-0.15)r_200 region
(where r_200 is the virial radius) the bolometric X-ray luminosity of the hot
gas is (4.3 +/- 0.8) x 10^40 erg/s and the gas mass is (9.1 +/- 0.9) x 10^9
M_sun. These values are comparable to those observed for the two other
well-studied X-ray coronae in spiral galaxies, suggesting that the physical
properties of such coronae are similar. This detection offers an excellent
opportunity for comparison of observations with detailed galaxy formation
simulations.
