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Type Ia supernova data have recently become strong enough to enable, for thefirst time, constraints on the time variation of the dark energy density andits equation of state. Most analyses, however, are using simple two orthree-parameter descriptions of the dark energy evolution, since it is wellknown that allowing more degrees of freedom introduces serious degeneracies.Here we present a method to produce uncorrelated and nearly model-independentband power estimates of the equation of state of dark energy and its density asa function of redshift. We apply the method to recently compiled supernovadata. Our results are consistent with the cosmological constant scenario, inagreement with other analyses that use traditional parameterizations, though wefind marginal (2-sigma) evidence for w(z) < -1 at z < 0.2. In addition to easyinterpretation, uncorrelated, localized band powers allow intuitive andpowerful testing of the constancy of either the energy density or equation ofstate. While we have used relatively coarse redshift binning suitable for thecurrent set of about 150 supernovae, this approach should reach its fullpotential in the future, when applied to thousands of supernovae found fromground and space, combined with complementary information from othercosmological probes.Comment: 5 pages, 2 figure

Uncorrelated estimates of dark energy evolution