Swift Precursors to Long GRBS: Hidden Signs of a Newly-Born, Hyper-Accreting Magnetar?

SWIFT PRECURSORS TO LONG GRBS: HIDDEN SIGNS OF A NEWLY-BORN HYPER-ACCRETING MAGNETAR?PRECURSORS TO THE PROMPT GAMMA-RAY BURST EMISSION HAVE ARGUABLY BEEN ONE OF THE BIGGEST SURPRISES OF THE SWIFT SATELLITE. THEY WERE NOT READILY PREDICTED BY THE COLLAPSAR MODEL AND THEIR INTERPRETATION STILL REMAINS ELUSIVE.AMONG THE VARIOUS SUGGESTED SCENARIOS AN ACCRETING MAGNETAR APPEARS PROMISING IN EXPLAINING SOME OF THE MAIN PRECURSOR FEATURES BY VIRTUE OF THE STRONG DYNAMICAL COUPLING BETWEEN ITS B-FIELD LINES AND THE ACCRETING PLASMA.HERE WE PROPOSE TO DEVELOP A QUANTITATIVE MODEL OF THIS SCENARIO WHICH COMPUTES THE FALLBACK MASS ACCRETION RATE FROM NUMERICAL MODELS OF THE COLLAPSING ENVELOPE OF THE PROGENITOR STAR AND GENERALIZES THE TORQUE EQUATIONS FOR MAGNETICALLY-THREADED DISKS TO THE HYPER-ACCRETING REGIME. BY MEANS OF A STATISTICAL COMPARISON BETWEEN THE NUMERICAL RESULTS AND THE SWIFT DATA WE AIM AT TESTING THEMAGNETAR MODEL FOR PRECURSORS.