GRB 980425/980712 repeater nature: GRBs as precessing Gamma Jets
ATel #31; Daniele Fargion
on 15 Jul 1998; 13:49 UT
Distributed as an Instant Email Notice Gamma-Ray Bursts
Credential Certification: Daniele Fargion (DANIELE.FARGION@ROMA1.INFN.IT)
Subjects: Optical, Gamma Ray, Gamma-Ray Burst, Soft Gamma-ray Repeater, Supernova Remnant
We notice that the two very recent GRBs on July 12 (by GCN Trigger n.6917 at UT 06:04:00:73 and , fifteen hours later , n.6918 at UT 21:06:07:13), are placed at coordinates (RA 292.6,Dec -47.6; RA 300.5,Dec -52) whose corresponding error boxes (3.4-18.2 deg) almost contains and /or overlaps the previous GRB980425 center associated to SN1998bw (at RA 291, Dec -52) IAUC # 6884 , # 6895 . The probability that these two last GRBs events on July would occur by chance in that sky region , since SN1998bw event, is below 10^{-3}. The consequent probable repeater nature of GRB980425 in nearby host galaxy ESO184-G82 probes the Gamma Jet precessing nature either for GRBs (as well as their link to SGRs) contrary to any candle isotropic GRB model (either fireball/ hypernovae or magnetar). The relativistic kinematics for the Gamma Jets (do to Inverse Compton Scattering) imply that only the inner core of gamma jets contains hard and intense gamma photons while external regions of the beam are softer and weaker.
Only nearest sources ( most intense ones ) may be (also) observed (as repeaters) in their wider beam periphery because of higher probability rate, due to wider cone cross section. Far away cosmic GRBs are observed rarely at their peak intensity near their SN birth and at their maximal power, while blazing to us within their inner and harder core beam .
Jet power decay make far cosmic GRBs no longer (easely) observable as repeaters. The geometrical variability of such multi precessing gamma jet (arc minute size for corresponding Lorentz factor>10^{3}) explains the statistics, the energetics and the puzzling morphology of GRBs and SGRs data either at near and far Universe regions. References: D.Fargion Preprint INFN 1215 on 13/07/98; D.Fargion,A.Salis " The time evolution of GRB spectra by a precessing lighthouse Gamma Jet", 749, GRB 3rdHuntsville Symposium 1996; #Astro-ph 9605166/9605167/9605168.
Daniele Fargion
