Abstract
Gamma-ray bursts (GRBs) display a bimodal duration distribution with a separation between the short- and long-duration bursts at about 2 s. The progenitors of long GRBs have been identified as massive stars based on their association with Type Ic core-collapse supernovae (SNe), their exclusive location in star-forming galaxies, and their strong correlation with bright UV regions within their host galaxies. Short GRBs have long been suspected on theoretical grounds to arise from compact object binary mergers (neutron star–neutron star or neutron star–black hole). The discovery of short GRB afterglows in 2005 provided the first insight into their energy scale and environments, as well as established a cosmological origin, a mix of host-galaxy types, and an absence of associated SNe. In this review, I summarize nearly a decade of short GRB afterglow and host-galaxy observations and use this information to shed light on the nature and properties of their progenitors, the energy scale and collimation of the relativistic outflow, and the properties of the circumburst environments. The preponderance of the evidence points to compact object binary progenitors, although some open questions remain. On the basis of this association, observations of short GRBs and their afterglows can shed light on the on- and off-axis electromagnetic counterparts of gravitational wave sources from the Advanced LIGO/Virgo experiments.
Highlights
Gamma-ray bursts (GRBs) are short, intense, and non-repeating flashes of ∼ MeV γ-rays with a wide range of spectral and temporal properties
Despite the broad diversity in their γ-ray emission properties, it was recognized primarily based on data from the Burst and Transient Source Experiment (BATSE) on-board the Compton Gamma-Ray Observatory that GRBs can be generally divided into two groups based on their duration and spectral hardness: the short-hard and long-soft bursts, with a separation at about 2 sec (Norris et al 1984, Dezalay et al 1992, Kouveliotou et al 1993)
The non-repeating nature of GRBs, their harder non-thermal spectra, and non-Euclidean space distribution separated them from the soft γ-ray repeaters (SGRs; e.g., Kouveliotou et al 1987, Laros et al 1987, Norris et al 1991), which originate from magnetars in the Milky Way and nearby galaxies (Kouveliotou et al 1998); it is important to note, that some events classified as short GRBs may represent extragalactic giant SGR flares with a long recurrence timescale (Abbott et al 2008, Ofek et al 2008, Hurley et al 2010, Abadie et al 2012b)
Summary
Gamma-ray bursts (GRBs) are short, intense, and non-repeating flashes of ∼ MeV γ-rays with a wide range of spectral and temporal properties. In addition to the comprehensive review of short GRBs presented here, I refer the reader to several previous reviews that provide additional insight on GRB theory and observations These include a review of GRBs in the BATSE era (Fishman & Meegan 1995); an early review of long GRB afterglow discoveries, the emerging GRB-supernova connection, and afterglow theory (van Paradijs, Kouveliotou & Wijers 2000); comprehensive reviews of the prompt emission and afterglow theory (Meszaros 2002, Piran 2004); a detailed review of the long GRB-supernova connection (Woosley & Bloom 2006); a preliminary review of short GRBs, focused primarily on theoretical issues, and including data from the first few well-localized events in 2005 (Nakar 2007); a comprehensive review of short GRB progenitor models, primarily compact object mergers and collisions (Lee & Ramirez-Ruiz 2007); a review of the primary early results from the Swift satellite, including in part the detections of short GRBs (Gehrels, Ramirez-Ruiz & Fox 2009); and an initial review of short GRB galactic and sub-galactic environments (Berger 2011)
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