Short GRB and their association with a binary mergers

This page provides some highlights about about short gamma-ray bursts (GRB) and their association with mergers of compact objects in binary systems: neutron star - neutron star systems and neutron star - black hole systems.

Features

Afterglow: lower energy and density scale than long GRB.
Spectra: harder than long GRB (α ≈ −0.4 versus ≈ −0.9, and a higher spectral peak, Epeak ≈ 400 versus ≈ 200 keV)
Progenitors: non-massive stars, NS+NS or NS+BH mergers. SMBH+star event is called a Tidal Disruption Event (TDE), and they are ultra-long GRB.
In contrast to long GRBs, short GRBs have ~0 sec spectral lag. Some high-luminosity long GRB (where lum. much higher than for sGRB) share similar property.
GeV emission with time delay 3s (0.6s for ~10GeV). Origin interpreted as hadronic / synchrotron-self-compton / afterglow.
Extended (softer) emission for ~1/4 of events.
Percurson emission, only 3 of 49 examples found in one study: (low sigma) 0.5 - 2.7 s prior main spike. Not clear if they are separate events. Possible source: magnetospheric interactions of compact objects, or NS crust shattering. Precursor emission is more clear for long GRB.
Jet break: change of decline rate in the emission light curve.

Models

High accretion rate and rapid rotation >>> energy extraction via neutrino-antineutrino annihilation or magnetohydrodynamic processes (e.g., Blandford & Znajek 1977, Rosswog & Ramirez-Ruiz 2002, Lee & Ramirez-Ruiz 2007) >>> collimated relativistic outflow.

Predictions

1) Occurrence in both late and early type galaxies due to wide range of possible delays between formation of binary and merger.
2) Some mergers at several kPc away from host galaxies due to natal kicks from NS/BH-forming supernovae
3) R-process nucleosynthesis from neutron-rich ejecta, kilonovae (Lattimer & Schramm 1976, Li & Paczyn ́ski 1998, Metzger et al. 2010b, Barnes & Kasen 2013)

References:

Berger, E., 2014. Short-duration gamma-ray bursts. Annual Review of Astronomy and Astrophysics, 52, pp.43-105.

Recent Work