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We present multiwavelength modeling of the afterglow from the long gamma-rayburst GRB 160625B using Markov Chain Monte Carlo (MCMC) techniques of theafterglowpy Python package. GRB 160625B is an extremely bright burst with arich set of observations spanning from radio to gamma-ray frequencies. Theseobservations range from ~0.1 days to >1000 days, thus making this eventextremely well-suited to such modeling. In this work we compare top-hat andGaussian jet structure types in order to find best fit values for the GRB jetcollimation angle, viewing angle, and other physical parameters. We find that aGaussian-shaped jet is preferred (2.7-5.3 sigma) over the traditional top-hatmodel. Our estimate for the opening angle of the burst ranges from 1.26 to 3.90degrees, depending on jet shape model. We also discuss the implications thatassumptions on jet shape, viewing angle, and particularly the participationfraction of electrons have on the final estimation of GRB intrinsic energyrelease and the resulting energy budget of the relativistic outflow. Mostnotably, allowing the participation fraction to vary results in an estimatedtotal relativistic energy of ~$10^{53}$ erg. This is two orders of magnitudehigher than when the total fraction is assumed to be unity, thus this parameterhas strong relevance for placing constraints on long GRB central engines,details of the circumburst media, and host environment.

GRB 160625B: Evidence for a Gaussian-Shaped Jet