EARLY OPTICAL-INFRARED EMISSION FROM GRB 041219a: NEUTRON-RICH INTERNAL SHOCKS AND A MILDLY MAGNETIZED EXTERNAL REVERSE SHOCK

摘要

Very early optical and near-infrared emission was discovered to have accompanied the long gamma-ray burst GRB 041219a. Here we show that the optical-IR flash tracking the gamma-ray light curve during the prompt emission can be understood as emission from neutron-rich internal shocks, as has been suggested by Fan & Wei. The early K_s-band afterglow light curve after the prompt phase can be well modeled as the superposition of a reverse and a forward shock component. The radio data also support the reverse-shock interpretation.