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_art. We show that the condensate fluctuations above the critical temperature T_c cause the fluctuational susceptibility, χ _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

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... nity of an accurate determination of T_c. We describe a method of measuring χ _fl which requires a constant gradient in B_art and suggest a way of creating such a field in experiment.