CLASH: PRECISE NEW CONSTRAINTS ON THE MASS PROFILE OF THE GALAXY CLUSTER A2261

We precisely constrain the inner mass profile of A2261 (z = 0.225) for the first time and determine that this cluster is not overconcentrated as found previously, implying a formation time in agreement with Lambda CDM expectations. These results are based on multiple strong-lensing analyses of new 16-band Hubble Space Telescope imaging obtained as part of the Cluster Lensing and Supernova survey with Hubble. Combining this with revised weak-lensing analyses of Subaru wide-field imaging with five-band Subaru + KPNO photometry, we place tight new constraints on the halo virial mass M-vir = (2.2 +/- 0.2) x 10(15) M-circle dot h(70)(-1) (within r(vir) approximate to 3 Mpc h(70)(-1)) and concentration c(vir) = 6.2 +/- 0.3 when assuming a spherical halo. This agrees broadly with average c(M, z) predictions from recent Lambda CDM simulations, which span 5 less than or similar to < c > less than or similar to 8. Our most significant systematic uncertainty is halo elongation along the line of sight (LOS). To estimate this, we also derive a mass profile based on archival Chandra X-ray observations and find it to be similar to 35% lower than our lensing-derived profile at r(2500) similar to 600 kpc. Agreement can be achieved by a halo elongated with a similar to 2:1 axis ratio along our LOS. For this elongated halo model, we find M-vir = (1.7 +/- 0.2) x 10(15) M-circle dot h(70)(-1) and c(vir) = 4.6 +/- 0.2, placing rough lower limits on these values. The need for halo elongation can be partially obviated by non-thermal pressure support and, perhaps entirely, by systematic errors in the X-ray mass measurements. We estimate the effect of background structures based on MMT/Hectospec spectroscopic redshifts and find that these tend to lower M-vir further by similar to 7% and increase c(vir) by similar to 5%.