The early stages of decelerating gamma-ray burst afterglow jets have been notoriously difficult to resolve numerically using two dimensional hydrodynamical simulations even at very high-resolution , due to the extreme thinness of the blast wave and high outflow Lorentz factors .
However , these resolution issues can be avoided by performing the simulations in a boosted frame , which makes it possible to calculate afterglow light curves from numerically computed flows in sufficient detail to accurately quantify the shape of the jet break and the post-break steepening of the light curve .
Here , we study afterglow jet breaks for jets with opening angles of 0.05 , 0.1 and 0.2 radians decelerating in a surrounding medium of constant density , observed at various angles ranging from on-axis to the edge of the jet .
A single set of scale-invariant functions describing the time evolution of afterglow synchrotron spectral break frequencies and peak flux , depending only on jet opening angle and observer angle , are all that is needed to reconstruct light curves for arbitrary explosion energy , circumburst density and synchrotron particle distribution power law slope p .
These functions are presented in the paper .
Their time evolutions change directly following the jet break , although an earlier reported temporary post-break steepening of the cooling break is found to have been resolution-induced .
We compare synthetic light curves to fit functions using sharp power law breaks as well as smooth power law transitions .
We confirm our earlier finding that the measured jet break time is very sensitive to the angle of the observer and can be postponed significantly .
We find that the difference in temporal indices across the jet break is larger than theoretically anticipated and is about - ( 0.5 + 0.5 p ) below the cooling break and about - ( 0.25 + 0.5 p ) above the cooling break , both leading to post-break slopes of roughly about 0.25 - 1.3 p , although different observer angles , jet opening angles and heuristic descriptions of the break introduce a wide range of temporal indices .
Nevertheless , the post-break slope from our constant density ISM simulations is sufficiently steep to be hard to reconcile with post-break slopes measured for the Swift sample , suggesting that Swift GRBs mostly do not explode in a homogeneous medium or that the jet breaks are hidden from view by additional physics such as prolonged energy injection or viewing angle effects .
A comparison between different smooth power law fit functions shows that although smooth power law transitions of the type introduced by Harrison et al .
1999 often provide better fits , smooth power law transitions of the type introduced by Beuermann et al .
1999 or even sharp power law fits are easier to interpret in terms of the underlying model .
Light curves and spectral break and peak flux evolution functions will be made publicly available on-line at http : //cosmo.nyu.edu/afterglowlibrary .