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We report on optical and NIR observations obtained during and after the 2004December discovery outburst of the X-ray transient and accretion-poweredmillisecond pulsar IGR J00291+5934. Our observations monitored the evolution ofthe brightness and the spectral properties of J00291 during the outburst decaytowards quiescence. We also present optical, NIR and Chandra observationsobtained during true quiescence. Photometry of the field during outburstreveals an optical and NIR counterpart that brightened from R~23 to R~17 andfrom K=19 to K~16. Spectral analysis of the RIJHK broadband photometry showsexcess in the NIR bands that may be due to synchrotron emission. The Halphaemission line profile suggests the orbital inclination is ~22-32 degrees. Thepreferred range for the reddening towards the source is 0.7 < E(B-V) < 0.9,which is equivalent to 4.06E21 cm^-2 < NH < 5.22E21 cm^-2. The Chandraobservations of the pulsar in its quiescent state gave an unabsorbed 0.5-10 keVflux for the best-fitting power-law model to the source spectrum of (7.0 +/-0.9)E-14 ergs/cm^2/s (adopting a hydrogen column of 4.6E21 cm^-2. The fitresulted in a power-law photon index of 2.4 +/- 0.5. The (R-K)o color observedduring quiescence supports an irradiated donor star and accretion disk. Weestimate a distance of 2 to 4 kpc towards J00291 by using the outburst X-raylight curve and the estimated critical X-ray luminosity necessary to keep theouter parts of the accretion disk ionized. Using the quiescent X-ray luminosityand the spin period, we constrain the magnetic field of the neutron star to be< 3E8 Gauss.Comment: 10 pages, 7 figures, 3 tables. Revision both in text and figures to  match the accepted manuscript to appear in Ap

Observations of the 599 Hz Accreting X‐Ray Pulsar IGR J00291+5934 during the 2004 Outburst and in Quiescence