GRB 090510 A Genuine Short GRB from a Binary Neutron Star Coalescing into a Kerr-Newman Black Hole

In a new classification of merging binary neutron stars (NSs) we separate short gamma-ray bursts (GRBs) into two subclasses. The ones with {E}<SUB>{iso</SUB>}≲ {10}<SUP>52</SUP> erg coalesce to form a massive NS and are indicated as short gamma-ray flashes (S-GRFs). The hardest, with {E}<SUB>{iso</SUB>}≳ {10}<SUP>52</SUP> erg, coalesce to form a black hole (BH) and are indicated as genuine short GRBs (S-GRBs). Within the fireshell model, S-GRBs exhibit three different components the proper GRB (P-GRB) emission, observed at the transparency of a self-accelerating baryon-{e}<SUP>+</SUP>{e}<SUP>-</SUP> plasma; the prompt emission, originating from the interaction of the accelerated baryons with the circumburst medium; and the high-energy (GeV) emission, observed after the P-GRB and indicating the formation of a BH. GRB 090510 gives the first evidence for the formation of a Kerr BH or, possibly, a Kerr-Newman BH. Its P-GRB spectrum can be fitted by a convolution of thermal spectra whose origin can be traced back to an axially symmetric dyadotorus. A large value of the angular momentum of the newborn BH is consistent with the large energetics of this S-GRB, which reach in the 1-10,000 keV range {E}<SUB>{iso</SUB>}=(3.95+/- 0.21) {10}<SUP>52</SUP> erg and in the 0.1-100 GeV range {E}<SUB>{LAT</SUB>}=(5.78+/- 0.60) {10}<SUP>52</SUP> erg, the most energetic GeV emission ever observed in S-GRBs. The theoretical redshift {z}<SUB>{th</SUB>}=0.75+/- 0.17 that we derive from the fireshell theory is consistent with the spectroscopic measurement z=0.903+/- 0.003, showing the self-consistency of the theoretical approach. All S-GRBs exhibit GeV emission, when inside the Fermi-LAT field of view, unlike S-GRFs, which never evidence it. The GeV emission appears to be the discriminant for the formation of a BH in GRBs, confirmed by their observed overall energetics.