GRB 140619B: a short GRB from a binary neutron star merger leading to black hole formation

Following the recent identification of the prototypical short GRB 090227B originating from a binary neutron star (NS) merger, leading to the formation of a black hole (BH), we present here a new example of such sources, GRB 140619B. The time-resolved spectral analysis performed on the Fermi-GBM data, allows for the identification of the characteristic features of the e + e - plasma at transparency (P-GRB) in the early 0:2 s of the GRB 140619B light curve: i.e., a thermal spectrum with an observed temperature kT = (324 33) keV which represents 40% of the total source fluence. The subsequent emission, with no evidence for a thermal spectrum, is identified with the prompt emission. We have consequently deduced a theoretical cosmological redshift of z = 2:67 0:37, a total burst energy E tot+e- = (6:03 0:79) 10 52 ergs, a baryon load B = (5:52 0:73) 10 -5 , and a Lorentz factor at transparency tr = (1:08 0:08) 10 4 . From the simulation of the prompt emission we have determined the average density of the circumburst medium (CBM),hnCBMi = (4:7 1:2) 10 -5 cm -3 , typical of the galactic halo environment. This low CBM density and the low baryon load, confirm the identification of the GRB progenitor as a NS‐NS merger. By assuming symmetric NS masses (MNS = 1:34 M ), the inferred baryon load corresponds to 3% of the total crustal mass, i.e. M2c = 7:26 10 -5 M . The corresponding emission of gravitational waves, in the inspiral phase up to the merger, corresponds to E T GW = 7:42 10 52 erg. We also show that the gravitational waves signal from the NS binary progenitor of GRB 140619B, in view of the large cosmological distance, is undetectable by the Advanced LIGO interferometer. Novel in this source is the presence of an observed emission at energies & 0:1 GeV lasting 5 s, with a total energy of ELAT = (2:02 0:52) 10 53 erg. We estimate the energy requirements of ELAT in terms of accretion of a fraction of M2c on the BH. From GRB 090227B and GRB 140619B, we have estimated the rate of such NS‐NS mergers, leading to BH formation, to be 0 = 1:7 +3:7 -1:4 10 -4 Gpc -3 yr -1 .