  We study the behaviour of ultracold bosonic gas in the critical region above
the Bose-Einstein condensation in the presence of an artificial magnetic field,
$B_\mathrm{art}$. We show that the condensate fluctuations above the critical
temperature $T_c$ cause the fluctuational susceptibility, $\chi _\mathrm{fl}$,
of a uniform gas to have a stronger power-law divergence than in an analogous
superconducting system. Measuring such a divergence opens new ways of exploring
critical properties of the ultracold gas and an opportunity of an accurate
determination of $T_c$. We describe a method of measuring $\chi _\mathrm{fl}$
which requires a constant gradient in $B_\mathrm{art}$ and suggest a way of
creating such a field in experiment.
