Continued Brightening of the Afterglow of GW170817/GRB 170817A as due to a Delayed Energy Injection

Understand

The brightness of the multi-wavelength afterglow of GRB 170817A is increasing unexpectedly even $\sim$ 160 days after the associated gravitational burst.

• Here we suggest that the brightening can be caused by a late-time energy injection process.
• We use an empirical expression to mimic the evolution of the injection luminosity, which is consisted of a power-law rising phase and a power-law decreasing phase.
• It is found that the power-law indices of the two phases are $0.92$ and $-2.8$, respectively, with the peak time of the injection being $\sim 110$ days.