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Discovery and confirmation of the shortest gamma-ray burst from a collapsar

An Author Correction to this article was published on 13 September 2021

This article has been updated


Gamma-ray bursts (GRBs) are among the brightest and most energetic events in the Universe. The duration and hardness distribution of GRBs has two clusters1, now understood to reflect (at least) two different progenitors2. Short-hard GRBs (SGRBs; T90 < 2 s) arise from compact binary mergers, and long-soft GRBs (LGRBs; T90 > 2 s) have been attributed to the collapse of peculiar massive stars (collapsars)3. The discovery of SN 1998bw/GRB 980425 (ref. 4) marked the first association of an LGRB with a collapsar, and AT 2017gfo (ref. 5)/GRB 170817A/GW170817 (ref. 6) marked the first association of an SGRB with a binary neutron star merger, which also produced a gravitational wave. Here, we present the discovery of ZTF20abwysqy (AT2020scz), a fast-fading optical transient in the Fermi satellite and the Interplanetary Network localization regions of GRB 200826A; X-ray and radio emission further confirm that this is the afterglow. Follow-up imaging (at rest-frame 16.5 days) reveals excess emission above the afterglow that cannot be explained as an underlying kilonova, but which is consistent with being the supernova. Although the GRB duration is short (rest-frame T90 of 0.65 s), our panchromatic follow-up data confirm a collapsar origin. GRB 200826A is the shortest LGRB found with an associated collapsar; it appears to sit on the brink between a successful and a failed collapsar. Our discovery is consistent with the hypothesis that most collapsars fail to produce ultra-relativistic jets.

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Fig. 1: Gamma-ray properties of GRB 200826A in context.
Fig. 2: Discovery of the afterglow of GRB 200826A.
Fig. 3: Panchromatic afterglow and collapsar confirmation.

Data availability

Upon request, the corresponding author will provide data required to reproduce the figures, including light curves and spectra for any objects. The authors note that most of these data are publicly available, either though ZTF, the Gemini archive (GN-DD-104), the Swift catalogue ( or GCNs .

Code availability

Upon request, the corresponding author will provide code (primarily in Python) used to produce the figures.

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This work was supported by the GROWTH (Global Relay of Observatories Watching Transients Happen) project funded by the National Science Foundation under PIRE grant No. 1545949. GROWTH is a collaborative project among California Institute of Technology (USA), University of Maryland College Park (USA), University of Wisconsin Milwaukee (USA), Texas Tech University (USA), San Diego State University (USA), University of Washington (USA), Los Alamos National Laboratory (USA), Tokyo Institute of Technology (Japan), National Central University (Taiwan), Indian Institute of Astrophysics (India), Indian Institute of Technology Bombay (India), Weizmann Institute of Science (Israel), The Oskar Klein Centre at Stockholm University (Sweden), Humboldt University (Germany), Liverpool John Moores University (UK) and University of Sydney (Australia). Based on observations obtained with the Samuel Oschin Telescope 48-inch and the 60-inch Telescope at the Palomar Observatory as part of the Zwicky Transient Facility project. ZTF is supported by the National Science Foundation under grant No. AST-1440341 and a collaboration including Caltech, IPAC, the Weizmann Institute for Science, the Oskar Klein Center at Stockholm University, the University of Maryland, the University of Washington (UW), Deutsches Elektronen-Synchrotron and Humboldt University, Los Alamos National Laboratories, the TANGO Consortium of Taiwan, the University of Wisconsin at Milwaukee and Lawrence Berkeley National Laboratories. Operations are conducted by Caltech Optical Observatories, IPAC and UW. The work is partly based on the observations made with the Gran Telescopio Canarias (GTC), installed in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofisica de Canarias, in the island of La Palma. The material is based on work supported by NASA under award No. 80GSFC17M0002. Based on observations obtained at the international Gemini Observatory, a program of NSF’s NOIRLab, which is managed by the Association of Universities for Research in Astronomy (AURA) under a cooperative agreement with the National Science Foundation on behalf of the Gemini Observatory partnership: the National Science Foundation (United States), National Research Council (Canada), Agencia Nacional de Investigación y Desarrollo (Chile), Ministerio de Ciencia, Tecnología e Innovación (Argentina), Ministério da Ciência, Tecnologia, Inovações e Comunicações (Brazil), and Korea Astronomy and Space Science Institute (Republic of Korea). The observations were obtained as part of Gemini Director’s Discretionary Program GN-2020B-DD-104. The Gemini data was processed using DRAGONS (Data Reduction for Astronomy from Gemini Observatory North and South). This work was enabled by observations made from the Gemini North telescope, located within the Maunakea Science Reserve and adjacent to the summit of Maunakea. We are grateful for the privilege of observing the Universe from a place that is unique in both its astronomical quality and its cultural significance. A.J.C.T. acknowledges all co-Is of the GTC proposal and the financial support from the State Agency for Research of the Spanish MCIU through the ‘Center of Excellence Severo Ochoa’ award to the Instituto de Astrofísica de Andalucía (SEV-2017-0709). The ZTF forced-photometry service was funded under the Heising-Simons Foundation grant No. 12540303 (PI: Graham). S.M. and J.M. acknowledge support from Science Foundation Ireland under grant No. 17/CDA/4723. R.D. acknowledges support from the Irish Research Council (IRC) under grant GOIPG/2019/2033. Analysis was performed on the YORP cluster administered by the Center for Theory and Computation, part of the Department of Astronomy at the University of Maryland. Resources supporting this work were provided by the NASA High-End Computing (HEC) Program through the NASA Advanced Supercomputing (NAS) Division at Ames Research Center. These results also made use of Lowell Observatory’s Lowell Discovery Telescope (LDT), formerly the Discovery Channel Telescope. Lowell operates the LDT in partnership with Boston University, Northern Arizona University, the University of Maryland and the University of Toledo. Partial support of the LDT was provided by Discovery Communications. LMI was built by Lowell Observatory using funds from the National Science Foundation (AST-1005313). M.W.C. acknowledges support from the National Science Foundation with grant No. PHY-2010970. S.A. gratefully acknowledges support from the GROWTH PIRE grant (1545949). Part of this research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration. E.C.K. acknowledges support from the G.R.E.A.T research environment and the Wenner-Gren Foundations. P.T.H.P. is supported by the research program of the Netherlands Organization for Scientific Research (NWO). H.K. is an LSSTC Data Science Fellow and thanks the LSSTC Data Science Fellowship Program, which is funded by LSSTC, NSF Cybertraining grant No. 1829740, the Brinson Foundation and the Moore Foundation; his participation in the program has benefited this work. S.M. and J.M. acknowledge support from Science Foundation Ireland under grant No. 17/CDA/4723. R.D. acknowledges support from the Irish Research Council (IRC) under grant GOIPG/2019/2033. P.C. is a Swarana Jayanti Fellow and acknowledges support from the Department of Science and Technology via award No. DST/SJF/PSA-01/2014-15). We thank the staff of the GMRT who made these observations possible. GMRT is run by the National Centre for Radio Astrophysics of the Tata Institute of Fundamental Research. P.C. is a Swarna Jayanti Fellow and thanks the Department of Science & Technology in India. We thank D. Bhattacharya, A. Vibhute and V. Shenoy for help with the CZTI analysis. V.A.F. acknowledges support from the RFBR 18-29-21030.

Author information




T.A. and L.P.S. were the primary authors of the manuscript. M.M.K. is the PI of GROWTH and the ZTF EM-GW program, and S.B.C. is PI of the SGRB program. M.W.C., S.A., I.A. and M.A. support development of the GROWTH ToO Marshal and associated program. H.K. and C.F. led the reductions of the Gemini data. E.Burns led analysis of the Fermi gamma-ray data. G.R., V.C., T.D. and P.T.H.P. contributed to the afterglow, KN and SN modelling. R.D. and J.M. were the GBM burst advocates and provided gamma-ray analysis. D.S.S., D.F., K.H., A.R. and A.T. performed IPN and Konus analyses. A.J.C.-T., A.F.V. and S.B.P. provided the GTC spectrum. K.D. performed the WIRC data reduction. P.C. and S.P. provided GMRT data. P.G., S.D. and E.T. provided the LDT data. E.H. performed galaxy and SED fitting. S.I. and V.B. performed the Astrosat analyses. C.C. contributed to the GROWTH Marshal. B.B., A.G.-Y., D.P., A.Y.Q.H., V.K., E.C.K., S.R., A.S.C. and R.Stein contributed to candidate scanning, vetting, and classification. E.Bellm., D.A.D., M.G., S.R.K., F.M., A.M., P.R., B.R., R.Smith., M.S. and R.W. are ZTF builders. All authors contributed to edits to the manuscript.

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Correspondence to Tomás Ahumada.

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Extended data

Extended Data Fig. 1 The AstroSat and Konus-Wind gamma-ray detections.

a, The de-trended light curve (blue) for GRB 200826A obtained from AstroSat CZTI data. We combined data from all four CZTI quadrants and binned it in 0.05 s bins. We fit and subtract a quadratic trend from the background to obtain zero-mean data. The shaded green region and corresponding green symbols denote a conservative GRB time span excluded from background trend estimation. Similarly red points denote outliers that are automatically flagged and rejected from the background estimate. b, A cumulative light curve (blue) obtained by summing the de-trended data, and normalised such that the median post-GRB value is 1.0. The dashed horizontal lines denote the 5% and 95% intensity levels. The corresponding vertical dotted black lines denote T05 and T95, yielding T90 of \(0.9{4}_{-0.18}^{+0.72}\) s. c, Rest-frame energetics of 331 Konus-Wind GRBs (SGRB: triangles, LGRB: circles) with known redshift in the EisoEpeak,z plane, with Epeak,z the rest frame Epeak. The hardness-intensity (‘Amati’) relation for LGRBs is plotted with its 68% and 90% prediction intervals (dark and light gray regions, respectively). GRB 200826A, as a red star, appears not to be consistent with the SGRB population.

Extended Data Fig. 2 Afterglow panchromatic observations.

Observations of the GRB 200826A afterglow and SN. GRB 200826A was triggered at Julian day 2459087.6874. The δt column shows the days from the trigger date.

Extended Data Fig. 3 Afterglow X-ray detections.

X-ray observations of GRB 200826A. The δt column shows the days from the trigger.

Extended Data Fig. 4 Radio data.

Radio observations of GRB 200826A. The δt column shows the days from the trigger. ** VLA data from Ref. 12.

Extended Data Fig. 5 Host galaxy panchromatic data.

Observations of the host galaxy of GRB 200826A. The δt column shows the days from the trigger. *Magnitudes are in the Vega system.

Extended Data Fig. 6 The Host Galaxy.

a, The GTC spectrum of the host galaxy and the lines used to determine a redshift of 0.748. b, The photometry of the host galaxy (ugrizJ, see Extended Data Table 2) in the AB system is presented in red circles, with their respective 1σ uncertainty. The best SED model and photometry from Prospector are shown in green. c, The pPXF host galaxy model results described in §1.3. The integrated spectrum (black) overlaid with the best-fit spectrum (orange), which sums the contributions of stars and gas in the modeled galaxy. The red spectrum shows the gas contribution to the spectrum, and the blue diamonds show the residuals to the fit. The gas is offset by 1.59e-18 erg s−1 cm−2. d, The pPXF weights (color bar) of the different stellar population templates used to construct the best-fit galaxy.

Extended Data Fig. 7 Host galaxy emission line fluxes.

Fluxes derived with pPXF for the lines detected in the GTC spectrum of the host galaxy.

Extended Data Fig. 8 SED sequence of the afterglow.

The SED of our model compared to observations at five epochs. Multiwavelenght data are shown as circles along their uncerntainties (1σ), while the 5σ upper-limits are shown as triangles (3σ for the radio data). The central line shows the posterior median flux density at each epoch, the dark band is the central 68% quantile (for example the 16-84% quantiles) and the lighter band is the central 95% quantile (2.5% to 97.5%). The cooling frequency νc is located at frequencies higher than 1 keV (that is νc > 2.4 × 1017 Hz). The glitches at optical ν ~ 1016 Hz are the edge of validity of our dust extinction model. The SN makes a large contribution at late times. See the observations in Extended Data Table 1,Extended Data Table 3, and Extended Data Table 4.

Extended Data Fig. 9 Posterior predictive plot for the GMOS i-band detection.

The posterior of the AB magnitude estimated at the time of the i-band data point ( ~ 28 days after the trigger) using afterglow only (blue) and afterglow-and-SN (orange) light curves are shown. The dashed black line shows the magnitude of the transient at ~ 28 days, an the grey area its 1σ uncertainty.

Extended Data Fig. 10 Afterglow properties.

Posterior afterglowpy fit model parameters with an SMC extinction curve, a SN1998bw template and including the final Gemini+GMOS detection. Uncertainties are quoted at 90%. Ek is the beamed corrected kinetic energy. See §1.4 for more details.

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Supplementary Table 1, Figs. 1 and 2

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Ahumada, T., Singer, L.P., Anand, S. et al. Discovery and confirmation of the shortest gamma-ray burst from a collapsar. Nat Astron 5, 917–927 (2021).

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