Robust features of off-axis gamma-ray burst afterglow light curves

ABSTRACT The ultra-relativistic outflows powering gamma-ray bursts (GRBs) acquire angular structure through their interaction with external material. They are often characterized by a compact, nearly uniform narrow core (with half-opening angle θc,{ϵ, Γ}) surrounded material energy per unit solid ($\epsilon =\epsilon _{\rm c}\Theta _{\epsilon }^{-a}$, where $\Theta _{\lbrace \epsilon ,\Gamma \rbrace }=[1+\theta ^2/\theta _{{\rm c},\lbrace }^2]^{1/2}$) and initial specific kinetic ($\Gamma _0-1=[\Gamma c}-1]\Theta _\Gamma ^{-b}$) declining as power laws. Multiwavelength afterglow light curves of off-axis jets viewing θobs > θc) offer robust ways to constrain a, b, the density radial profile (ρ ∝ R−k), even while other burst parameters may remain highly degenerate. We extend our previous work on such afterglows include more realistic profiles derived from three-dimensional hydrodynamic simulations both long short GRBs (addressing also shallow profiles, whose emission exhibits unique evolution). present based parametrized power-law jet for different angles k = {0, 1, 2}. identify evolutionary phase characteristic synchrotron frequencies (νm νc) that manifests when curve is dominated sensitive outflow. calculate criterion obtaining single or double peaked in general case θc,Γ ≠ θc,ϵ. emphasize how shape temporal evolution νm νc can be used outflow potentially distinguish between magnetic jets.