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) in two sub-classes. The ones with
$E_{iso}\lesssim10^{52}$ erg coalesce to form a massive NS and are indicated as
short gamma-ray flashes (S-GRFs). The hardest, with $E_{iso}\gtrsim10^{52}$
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 P-GRB emission, observed at the transparency of a
self-accelerating baryon-$e^+e^-$ plasma; the prompt emission, originating from
the interaction of the accelerated baryons with the circumburst medium; 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--10000 keV range $E_{iso}=(3.95\pm0.21)\times10^{52}$ erg and in the 0.1--100
GeV range $E_{LAT}=(5.78\pm0.60)\times10^{52}$ erg, the most energetic GeV
emission ever observed in S-GRBs. The theoretical redshift $z_{th}=0.75\pm0.17$
that we derive from the fireshell theory is consistent with the spectroscopic
measurement $z=0.903\pm0.003$, 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.
