How Special Is GRB 170817A?

Understand

GRB 170817A is the first short gamma-ray burst (GRB) with direct detection of the gravitational-wave radiation and also the spectroscopically identified macronova emission (i.e., AT 2017gfo).

• The prompt emission of this burst, however, is underluminous in comparison with the other short GRBs with known redshift.
• In this work, we examine whether GRB 170817A is indeed unique.
• We firstly show that GRB 130603B/macronova may be the on-axis "analogs" of GRB 170817A/AT 2017gfo, and the extremely dim { but long-lasting} afterglow emission of GRB 170817A may suggest a low number density ($\sim 10^{-5}~{\rm cm^{-3}}$) of its circumburst medium { and a structured outflow}.