X Ray Precursors in SGRs: Precessing Gamma Jet Tails

Abstract

Weak isolated X-ray precursor events before the main Gamma Ray Burst, GRB, and also rare Soft Gamma Repeaters, SGR, events are in complete disagreement with any Fireball, or Magnetar, one-shoot explosive scenarios. Fireball model in last two years has been deeply modified into a fountain beamed Jet exploding and interacting on external shells to explain GRB fine time structure. On the contrary earlier we proposed a unified scenario for both GRBs-SGRs where a precessing Gamma Jet (of different intensity) and its geometrical beaming is the source of both GRB and SGRs wide morphology. GRBs are peaked SNs Jet spinning and precessing observed along the thin Jet axis. Their mysterious weak X precursors bursts, corresponding to non-negligible energy powers, up to million Supernova ones for GRB, are gamma Jet tails beamed off-axis, observed at X-Ray tails. They are rare, about (3-6)% of all GRBs, but not unique at all. Comparable brief X-ray precursor flashes occurred in rarest and most detailed SGRs events as the 27 and the 29 August 1998 event from SGR 1900+14. The same source has been in very power-full activity on recent 18 April 2001 once again preceded by X-Ray precursors. These events are inconsistent with any Fireball or Magnetar-Mini-Fireball models. We interpret them naturally as earlier marginal blazing of outlying X conical precessing Jet, an off-axis tails surrounding a narrower gamma precessing Jet. Only when the light-house Jet is in on-axis blazing mode toward the Earth we observe the harder power-full SGR event. We predict such a rich X-Ray precursor signals (more numerous then gamma ones) during Soft Gamma Repeater peak activities; they should be abundant and within detection threshold by a permanent monitoring SGRs by Beppo-Sax WFC or Chandra X ray satellites while at peak activity.