GRB outflows have neutrons

• Current engine models naturally predict

• n/p>1 (Ye<0.5)

• (Derishev et al 99, Beloborodov 03, Pruet at al 03)

• GRB jets are powered by a high rate accretio

• disk of ~ Msun per sec around a solar mass BH

  • (Woosley 93, Eichler et al. 89, Janka et al. 99&01,
  • Vietri&Stella 98, Zhang&Fryer 01 , Fryer et al. 99)

Notes: