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RJK Band Observations of the Optical Afterglow of GRB 991216

2000; IOP Publishing; Volume: 543; Issue: 1 Linguagem: Inglês

10.1086/317102

1538-4357

P. Garnavich, Saurabh W. Jha, M. A. Pahre, Krzysztof Z. Stanek, R. Kirshner, M. R. Garcia, Andrew Szentgyorgyi, J. Tonry,

Astrophysical Phenomena and Observations

We 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 ν-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.