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Register a new userA Peculiarly Short-duration Gamma-Ray Burst from Massive Star Core Collapse
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Gamma-ray bursts (GRBs) have been phenomenologically classified into long and short populations based on the observed bimodal distribution of duration. Multi-wavelength and multi-messenger observations in recent years have revealed that in general long GRBs originate from massive star core collapse events, whereas short GRBs originate from binary neutron star mergers. 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. Some apparently long GRBs have been suggested to have a neutron star merger origin, whereas some apparently short GRBs have been attributed to genuinely long GRBs whose short, bright emission is slightly above the detectors sensitivity threshold. Here we report the comprehensive analysis of the multi-wavelength data of a bright short GRB 200826A. Characterized by a sharp pulse, this burst shows a duration of 1 second and no evidence of an underlying longer-duration event. Its other observational properties such as its spectral behaviors, total energy, and host galaxy offset, are, however, inconsistent with those of other short GRBs believed to originate from binary neutron star mergers. Rather, these properties resemble those of long GRBs. This burst confirms the existence of short duration GRBs with stellar core-collapse origin, and presents some challenges to the existing models.
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Long-duration gamma-ray bursts (GRBs) are understood to be the final fate for a subset of massive, stripped envelope, rapidly rotating stars. Beyond this, our knowledge of the progenitor systems is limited. Using the BPASS (Binary Population and Spectral Synthesis) stellar evolution models, we investigate the possibility that some massive stars in binaries can maintain the angular momentum required for jet production, while still loosing their outer envelope through winds or binary interactions. We find that a total hydrogen mass of less than 0.0005 Msun and a helium ejecta mass fraction of less than 0.20 provide the best thresholds for the supernova type II/Ibc and Ib/Ic divisions respectively. Tidal interactions in binaries are accounted for by applying a tidal algorithm to post-process the stellar evolution models output by BPASS. We show that the observed volumetric gamma-ray burst rate evolution can be recreated using two distinct pathways and plausible distributions for burst parameters. In the first pathway, stars are spun up by mass accretion into a quasi-homogeneous state. In the second, tides maintain rotation where otherwise the star would spin down. Both lead to type Ic supernova progenitors, and a metallicity distribution consistent with the GRB host galaxy population. The inferred core angular momentum threshold for jet production is consistent with theoretical requirements for collapsars, given the assumptions made in our model. We can therefore reproduce several aspects of core collapse supernova/GRB observation and theory simultaneously. We discuss the predicted observable properties of GRB progenitors and their surviving companions.
Gamma-ray bursts (GRBs) display a bimodal duration distribution, with a separation between the short- and long-duration bursts at about 2 sec. The progenitors of long GRBs have been identified as massive stars based on their association with Type Ic core-collapse supernovae, their exclusive location in star-forming galaxies, and their strong correlation with bright ultraviolet regions within their host galaxies. Short GRBs have long been suspected on theoretical grounds to arise from compact object binary mergers (NS-NS or NS-BH). The discovery of short GRB afterglows in 2005, provided the first insight into their energy scale and environments, established a cosmological origin, a mix of host galaxy types, and an absence of associated supernovae. 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. Based on 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.
Gamma-ray bursts (GRBs) show a bimodal distribution of durations, separated at a duration of ~2 s. Observations have confirmed the association of long GRBs with the collapse of massive stars. The origin of short GRBs is still being explored. We examine constraints on the emission region size in short and long GRBs detected by Fermi/GBM. We find that the emission region size during the prompt emission, R, and the burst duration, T$_{90}$, are consistent with the relation R ~ c x T$_{90}$, for both long and short GRBs. We find the characteristic size for the prompt emission region to be ~2 x 10$^{10}$ cm, and ~4 x 10$^{11}$ cm for short and long GRBs, respectively.
Double neutron star (DNS) merger events are promosing candidates of short Gamma-ray Burst (sGRB) progenitors as well as high-frequecy gravitational wave (GW) emitters. On August 17, 2017, such a coinciding event was detected by both the LIGO-Virgo gravitational wave detector network as GW170817 and Gamma-Ray Monitor on board NASAs {it Fermi} Space Telescope as GRB 170817A. Here we show that the fluence and spectral peak energy of this sGRB fall into the lower portion of the distributions of known sGRBs. Its peak isotropic luminosity is abnormally low. The estimated event rate density above this luminosity is at least $190^{+440}_{-160} {rm Gpc^{-3} yr^{-1}}$, which is close to but still below the DNS merger event rate density. This event likely originates from a structured jet viewed from a large viewing angle. There are similar faint soft GRBs in the {it Fermi} archival data, a small fraction of which might belong to this new population of nearby, low-luminosity sGRBs.
Aims. With an observed and rest-frame duration of < 2s and < 0.5s, respectively, GRB090426 could be classified as a short GRB. The prompt detection, both from space and ground-based telescopes, of a bright optical counterpart to this GRB offered a unique opportunity to complete a detailed study. Methods. Based on an extensive ground-based observational campaign, we obtained the spectrum of the optical afterglow of GRB090426, measuring its redshift and obtaining information about the medium in which the event took place. We completed follow-up observation of the afterglow optical light curve down to the brightness level of the host galaxy that we firmly identified and studied. We also retrieved and analyzed all the available high-energy data of this event, and compared the results with our findings in the optical. This represents one of the most detailed studies of a short-duration event presented so far. Results. The time properties qualify GRB090426 as a short burst. In this case, its redshift of z = 2.61 would be the highest yet found for a GRB of this class. On the other hand, the spectral and energy properties are more similar to those of long bursts. LBT late-time deep imaging identifies a star-forming galaxy at a redshift consistent with that of the GRB. The afterglow lies within the light of its host and shows evidence of local absorption.
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