Gamma ray burst progenitors

We follow the evolution of binary systems that include rotational processes for both stars. Neglecting magnetic fields, we show that the cores of massive stars can maintain a high specific angular momentum (j~10<SUP>17</SUP> cm<SUP>2</SUP> s<SUP>-1</SUP>) when evolved with the assumption that mean molecular weight gradient suppress rotational mixing processes. We also present models that include magnetic fields generated by differential rotation (Spruit 2002) and we consider the internal angular momentum transport by magnetic torques. We show that the magnetic coupling of core and envelope after the accreting star ends core hydrogen burning leads to slower rotation (j~10<SUP>15-16</SUP> cm<SUP>2</SUP> s<SUP>-1</SUP>) than in the non-magnetic case