Garnavich, Peter M.Jha, SaurabhPahre, Michael A.Stanek, Krzysztof Z.Kirshner, Robert P.Garcia, Michael R.Szentgyorgyi, Andrew H.Tonry, John L.2019-09-252000Garnavich, Peter M., Saurabh Jha, Michael A. Pahre, Krzysztof Z. Stanek, Robert P. Kirshner, Michael R. Garcia, Andrew H. Szentgyorgyi, and John L. Tonry. 2000. “RJKBand Observations of the Optical Afterglow of GRB 991216.” The Astrophysical Journal 543 (1): 61–65. https://doi.org/10.1086/317102.0004-637X1538-4357http://nrs.harvard.edu/urn-3:HUL.InstRepos:41399854We present near-infrared and optical observations of the afterglow to the gamma-ray burst 991216 obtained with the Fred L. Whipple Observatory 1.2 m telescope and the University of Hawaii 2.2 m telescope. The observations range from 15 hours to 3.8 days after the burst. The temporal behavior of the data is well described by a single power-law decay t(-1.36+/-0.04), independent of wavelength. The optical spectral energy distribution, which is corrected for significant Galactic reddening of E(B-V) = 0.626, is well fitted by a single power law with v(-0.58+/-0.08). Combining the IR/optical observations with a Chandra X-Ray Observatory measurement gives a spectral index of -0.8 +/- 0.1 in the synchrotron cooling regime. A comparison between the spectral and temporal power-law indices suggests that a jet is a better match to the observations than a simple spherical shock.en-USJournal Article2019-09-2510.1086/317102