X Ray Precursors in GRBs and SGRs: outer X tails around a Precessing   Gamma Jet
  Weak isolated X-ray precursor events before the main Gamma Ray Burst, GRB, and also rare Soft Gamma Repeaters, SGR, events are in disagreement with any Fireball, or Magnetar, scenarios.   These models are originated by an unique explosive event leading, by internal-external shock waves, to softer secondary trains following a main gamma signals. Indeed the earliest GRB980519,GRB981226 events as well as the latest and most distant identified one as GRB000131 are showing rare but well identified and distinct X Ray precursor, occurring tens of seconds or even a minute before the main GRB eruption. These weak X precursors bursts correspond to non-negligible energy powers, up to million Supernova ones.   They are rare, about (3-6)% of all GRBs, but not unique.   Similar huge explosive precursor are in total disagreement with a successive main Fireball GRB outburst.   Comparable brief X-ray precursor flashes are found also in rarest and most detailed SGRs events as those observed on 27 and 29 August 1999 from SGR 1900+14.   They are inconsistent with a Magnetar Fireball explosion.   We interpret them as earlier marginal blazing of outlying X conical Jet tails surrounding a narrower gamma precessing,spinning beamed Jet in blazing mode toward the Earth; later re-crossing and better hitting of the target -the satellite detectors- is source of the main GRB (and SGR) observed structured event.   The X Ray precursor existence is an additional remarkable evidence of the Precessing relativistic Jet Nature of both GRBs and SGRs. 
Daniele Fargion (Physics Department and INFN, Ple.A.Moro 2, Rome,   Italy)