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# A peculiarly short-duration gamma-ray burst from massive star core collapse

## Abstract

Gamma-ray bursts (GRBs) have been phenomenologically classified into long and short populations based on the observed bimodal distribution of duration1. Multi-wavelength and multi-messenger observations in recent years have revealed that in general long GRBs originate from massive star core collapse events2, whereas short GRBs originate from binary neutron star mergers3. 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 GRB4. Some apparently long GRBs have been suggested to have a neutron star merger origin5, whereas some apparently short GRBs have been attributed to genuinely long GRBs6 whose short, bright emission is slightly above the detector’s sensitivity threshold. Here, we report the comprehensive analysis of the multi-wavelength data of the short, bright 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 behaviours, 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 origin4, and presents some challenges to the existing models.

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## Data availability

Processed data are presented in the tables and figures in the paper. Source and optical observational data are available upon reasonable request to the corresponding authors. The Fermi GBM data are publicly available at https://heasarc.gsfc.nasa.gov/FTP/fermi/data/.

## Code availability

Upon reasonable request, the code (mostly in Python) used to produce the results and figures will be provided.

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## Acknowledgements

B.-B.Z. acknowledges support by the National Key Research and Development Programs of China (2018YFA0404204), the National Natural Science Foundation of China (grant nos. 11833003 and U2038105) and the Innovative and Entrepreneurial Talent Program in Jiangsu. Y.-Z.M. is supported by the National Postdoctoral Program for Innovative Talents (grant no. BX20200164). This work was supported in part by the Natural Science Foundation of China (grant nos. U1831135 (X.-H.Z.), 11922301 (H.-J.L.), 12041306 (Y.L.) and U1938201 (X.-G.W.)), the Guangxi Science Foundation (2017GXNSFFA198008 (H.-J.L.), 2017AD22006 (X.-G.W.) and 2016GXNSFFA380006 (X.-G.W.)) and the Bagui Young Scholars Program (H.-J.L.). Part of this work is based on observations made with the GTC installed at the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofisica de Canarias, on the island of La Palma. We also acknowledge the use of public data from the Fermi Science Support Center.

## Author information

Authors

### Contributions

B.-B.Z. and H.-J.L. initiated the study. B.-B.Z. and B.Z. coordinated the scientific investigations of the event. B.-B.Z., Z.-K.L., Z.-K.P., Y.L., H.-J.L., J.Y., Y.-S.Y., Y.-H.Y., Y.-Z.M. and J.-H.Z. processed and analysed the data. A.J.C.-T. and Y.-D.H. carried out the GTC optical observations. J.-R.M., X.-H.Z. and J.-M.B. carried out the Lijiang 2.4 m optical observations. X.-G.W. and E.-W.L. carried out the LCOGT observations. B.Z. and Z.-G.D. contributed to the theoretical interpretations of the event. B.-B.Z. and B.Z. wrote the paper with contributions from all coauthors and the help of H.-Y.Y. on the format and language.

### Corresponding authors

Correspondence to B.-B. Zhang or B. Zhang.

## Ethics declarations

### Competing interests

The authors declare no competing interests.

Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

## Extended data

### Extended Data Fig. 1 Spectral fitting results of GRB 200826A.

The table shows the time-integrated and time-resolved spectral fitting results of GRB 200826A with cutoff power law model.

### Extended Data Fig. 2 Spectral fitting results within the interval from T0+0.50s to T0+ 1.60 s.

Spectral fitting results within the interval of T0 + 0.50s ~ T0 + 1.60s. a, observed photon count rate spectra and fitted model of nb(red), n7(blue) and b1(sky blue) detectors. b, de-convolved spectra(black points) and best-fit power law model(red line). c, corner plots and histograms show one and two-dimensional posterior probability distributions of cutoff power-law model parameters at 1-σ (purple contours), 2-σ(yellow contours) and 3-σ(green contours) confidence levels. Red error bars and crosses represent best-fit values with 1-σ uncertainties.

### Extended Data Fig. 3 Spectral evolution of GRB 200826A.

Spectral evolution of GRB 200826A. Panels a and b show evolution of the photon index (α) and spectral peak energy (Ep) of the cut-off powelaw model, respectively. Panels c and d show the NaI and BGO light curves. All error bars represent 1-σ uncertainties.

### Extended Data Fig. 4 Spectral lag calculation.

Spectral lag calculation. a, light curves in different energy bands(10-20 keV ~ 300-500 keV) which are used to calculate lags. b, energy dependent spectral lag between the lowest energy(10-20 keV) band and any higher energy band. All error bars represent 1-σ uncertainties.

### Extended Data Fig. 5 Detailed optical observations.

The table shows the observations of the optical counterpart and host galaxy of GRB 200826A.

### Extended Data Fig. 6 X-ray afterglow of GRB 200826A.

X-ray afterglow of GRB 200826A. Black points represents the observed X-ray flux in 0.3-10 keV. The solid orange line shows the broken power-law fitting with slopes α = -1.41$${}_{-0.12}^{+0.24}$$, β= -0.43$${}_{-0.22}^{+0.17}$$ and a break at tb = $$1.5{1}_{-0.30}^{+0.31}\times 1{0}^{5}$$ s. The dashed blue line represents the magnetar spin-down energy injection model parameterized by Lsd = L0(1+t/τ)−2 with L0 = 1044.9ergs−1 and τ = 1.0 × 106s. All error bars represent 1-σ uncertainties. The upper limit is at the 3-σ level.

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Zhang, BB., Liu, ZK., Peng, ZK. et al. A peculiarly short-duration gamma-ray burst from massive star core collapse. Nat Astron 5, 911–916 (2021). https://doi.org/10.1038/s41550-021-01395-z

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