Gamma-ray bursts (GRBs) have been phenomenologically classified into long and short populations based on whether the observed duration is longer or shorter than two seconds 1 .Multi-wavelength and multi-messenger observations in recent years have revealed that in general long GRBs originate from massive star core collapse events 2 , whereas short GRBs originate from binary neutron star mergers 3 . It has been known that the duration criterion is sometimes unreliable, and multi-wavelength criteria are needed to identify the physical origin of a particular GRB 4 . Some apparently long GRBs have been suggested to have a neutron star merger origin 5 , whereas some apparently short GRBs have been attributed to genuinely long GRBs 6 whose short, bright emission is above the detector's sensitivity threshold. Still, there has been no known case that a GRB is genuinely short but originates from death of a massive star. Here we report the comprehensive analysis of the multi-wavelength data of a bright short GRB 200826A. This burst has a sharp 1-second spike, which is not part of an underlying long-duration event. Its other observational properties are, however,

We perform a stringent search for precursor emission of short gamma-ray bursts (SGRBs) from the Fermi/GBM data and find 16 precursor events with ≳4.5σ significance. We find that the durations of the main SGRB emission ( ) and the precursor emission ( ), as well as the waiting time ( ) in between, are roughly comparable to each other, with  ≈ 2.8 1.2 approximately satisfied for most cases except one significant outlier. We also perform spectral analyses to the precursors and SGRBs, and find that the spectra of precursor emission can be fitted with the blackbody, nonthermal cutoff power law and/or power-law models. We consider several possible models for precursor emission in SGRBs and find that the luminosity and spectral shape may be explained by the the shock breakout or the photospheric radiation of a fireball launched after the merger for thermal precursors, or magnetospheric interaction between two neutron stars prior to the merger for nonthermal precursors. For the fireball photospheric model, a matter-dominated jet is preferred and a constraint on the fireball Lorentz factor can be placed as Γ ∼ 30. For the magnetospheric interaction model, the jet launching mechanism may be constrained. In particular, those events with /  ≫ 1 (e.g., GRB191221802) require the formation of a supramassive or stable neutron star after the merger, with the delay time defined by the timescale for an initially baryon-loaded jet to become magnetically dominated and relativistic.

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We investigate the prompt emission and the afterglow properties of short-duration gamma-ray burst (sGRB) 130603B and another eight sGRB events during 2012–2015, observed by several multiwavelength facilities including the Gran Canarias Telescope 10.4 m telescope. Prompt emission high energy data of the events were obtained by INTEGRAL-SPI-ACS, Swift-BAT, and Fermi-GBM satellites. The prompt emission data by INTEGRAL in the energy range of 0.1–10 MeV for sGRB 130603B, sGRB 140606A, sGRB 140930B, sGRB 141212A, and sGRB 151228A do not show any signature of the extended emission or precursor activity and their spectral and temporal properties are similar to those seen in case of other short bursts. For sGRB 130603B, our new afterglow photometric data constrain the pre-jet-break temporal decay due to denser temporal coverage. For sGRB 130603B, the afterglow light curve, containing both our new and previously published photometric data is broadly consistent with the ISM afterglow model. Modeling of the host galaxies of sGRB 130603B and sGRB 141212A using the LePHARE software supports a scenario in which the environment of the burst is undergoing moderate star formation activity. From the inclusion of our late-time data for eight other sGRBs we are able to: place tight constraints on the non-detection of the afterglow, host galaxy, or any underlying ‘kilonova’ emission. Our late-time afterglow observations of the sGRB 170817A/GW170817 are also discussed and compared with the sub-set of sGRBs.

Recently two fast X-ray transients (XT1 and XT2) have been reported from the search in the Chandra Deep Field (CDF) data. Each transient shows an initial plateau lasting around hundreds to thousands seconds followed by a rapid decay in the light curve. In particular, CDF-S XT2 is found to be associated with a galaxy at redshift z = 0.738 and was explained as a counterpart of a binary neutron-star merger event. In this paper, motivated by the short duration and decay slopes of the two transients, we consider an alternative interpretation in which both events are accretion-driven flares from tidal disruption of white dwarfs by intermediate-mass black holes. We derive a theoretical model of the accretion rate history, and find that it fits the observed X-ray light curves well. The extremely super-Eddington peak luminosity of XT2 can be explained by the beaming effect of the system, likely in the form of a jet.