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Evidence for a brief appearance of gamma-ray periodicity after a compact star merger

Nature Astronomy (2025)Cite this article

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Abstract

The product of a compact star merger is usually hypothesized to be a hyperaccreting black hole, typically resulting in a gamma-ray burst (GRB) with a duration shorter than 2 s. However, recent observations of GRB 211211A and GRB 230307A, both arising from compact star mergers, challenge this model due to their minute-long durations. The data from both events are consistent with having a nascent, rapidly spinning, highly magnetized neutron star (a millisecond magnetar) as the merger product and GRB engine, but a smoking gun signature is still missing. Here we report strong but not yet conclusive evidence for the detection of a 909-Hz gamma-ray periodic signal during a brief time window of GRB 230307A, which is consistent with the rotation frequency of such a millisecond magnetar. Notably, the periodic signal appeared for only 160 ms at an epoch coinciding with the transition epoch when the jet emission from the GRB central engine ceased and when the delayed emission from high latitudes started. If this signal is real, the temporal and spectral features of this gamma-ray periodicity can be consistently interpreted as asymmetric mini-jet emission from a dissipating Poynting-flux-dominated jet, as revealed by the energy-dependent light curve data of this burst.

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Fig. 1: Results of blind search for periodicity in GRB 230307A.
Fig. 2: Occurrence and harmonics of the QPO signal from GRB 230307A.
Fig. 3: Detections of consistent QPOs in GRB 230307A with several instruments.
Fig. 4: A physical scenario to interpret the 909-Hz signal from GRB 230307A.

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Data availability

The processed data presented in the tables and figures of the paper are available upon reasonable request. Some of the data used in this study are accessible through the NASA/Fermi Data Archive, the GECAM Data Archive or GRB Coordinates Network circulars. For GECAM data for GRB 230307A, which are at present under the protection period and not publicly accessible, researchers or organizations may submit a reasonable request by email to obtain and use the proprietary data. For data access inquiries, please contact S.-L.X. (xiongsl@ihep.ac.cn).

Code availability

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

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Acknowledgements

We thank Z.-Y. Yan, R.-F. Shen and H. Gao for helpful comments. We are grateful to the GECAM team for the development and operation of the GECAM mission. The GECAM mission is supported by the Strategic Priority Research Programme on Space Science of the Chinese Academy of Sciences. This work was supported by the National Key Research and Development Programmes of China (grants 2022YFF0711404 and 2022SKA0130102 to B.-B.Z. and 2021YFA0718500 to S.-L.X., C.-W.W., W.-J.T. and S.-N.Z.), the National SKA Programme of China (grant 2022SKA0130100 to B.-B.Z.), the Strategic Priority Research Programme of the Chinese Academy of Sciences (grant XDA15360102, XDA15360300 and XDB0550300 to S.-L.X., C.-W.W., W.-J.T. and S.-N.Z.) and the National Natural Science Foundation of China (grant 11833003, U2038105 and 12121003 to B.-B.Z., 13001106 to J.Y., 12273042 and 12494572 to S.-L.X., C.-W.W. and W.-J.T. and 12333007 to S.-N.Z.). B.-B.Z acknowledges the support of science research grants from the China Manned Space Programme (grant CMS-CSST-2021-B11), the Fundamental Research Funds for the Central Universities and the Programme for Innovative Talents and Entrepreneurs in Jiangsu. This work was performed on an HPC server equipped with two Intel Xeon Gold 6248 processors at Nanjing University. We acknowledge IT support from the computer lab of the School of Astronomy and Space Science at Nanjing University.

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Authors and Affiliations

  1. School of Astronomy and Space Science, Nanjing University, Nanjing, P. R. China

    Run-Chao Chen, Bin-Bin Zhang, Jun Yang & Yi-Han Iris Yin

  2. Key Laboratory of Modern Astronomy and Astrophysics, Nanjing University, Ministry of Education, Nanjing, P. R. China

    Run-Chao Chen, Bin-Bin Zhang, Jun Yang & Yi-Han Iris Yin

  3. Purple Mountain Observatory, Chinese Academy of Sciences, Nanjing, P. R. China

    Bin-Bin Zhang

  4. State Key Laboratory of Particle Astrophysics, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing, P. R. China

    Chen-Wei Wang, Wen-Jun Tan, Shao-Lin Xiong & Shuang-Nan Zhang

  5. University of Chinese Academy of Sciences, Chinese Academy of Sciences, Beijing, China

    Chen-Wei Wang, Wen-Jun Tan & Shuang-Nan Zhang

  6. Department of Physics, The University of Hong Kong, Hong Kong, China

    Bing Zhang

  7. Nevada Center for Astrophysics and Department of Physics and Astronomy, University of Nevada, Las Vegas, Las Vegas, NV, USA

    Bing Zhang

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Contributions

R.-C.C. and B.-B.Z. initiated the study. B.-B.Z., B.Z. and R.-C.C. coordinated the scientific investigations of the event. R.-C.C., J.Y. and Y.-H.I.Y. performed the published data acquisition. R.-C.C. processed and analysed the Fermi/GBM data. R.-C.C., J.Y., C.-W.W., W.-J.T. and S.-L.X. processed and analysed the GECAM data, investigated the statistical methods, performed the periodicity search, and conducted the validation and significance estimation of the QPO. R.-C.C. and J.Y. investigated and applied the Bayesian inference method and performed the power spectral fitting for the QPO. R.-C.C. conducted the temporal and spectral analysis of the QPO. B.Z. and B.-B.Z. provided the idea for the physical interpretation of the QPO. R.-C.C., Y.-H.I.Y., J.Y., B.-B.Z. and B.Z. investigated the physical model, produced the schematic diagram and contributed to the discussion of the physical implications. R.-C.C., B.-B.Z., B.Z., C.-W.W., W.-J.T, S.-L.X., J.Y., Y.-H.I.Y. and S.-N.Z. contributed to discussions about the results. R.-C.C., B.-B.Z. and B.Z. wrote the paper, with contributions from all authors.

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Correspondence to Bin-Bin Zhang, Shao-Lin Xiong or Bing Zhang.

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Extended data

Extended Data Fig. 1 Consistent detection of the 909-Hz QPO across multiple detectors on GECAM-B.

The incident angles to GRB 230307A for each detector are presented in brackets following the detector names. a, Dynamical power spectra based on \({Z}_{1}^{2}\) statistics calculated from overlapping 160-ms intervals spaced at 7 ms. TTE data are extracted within the energy range of 98-248 keV from each detector individually. The red box marks the time interval of [24.401, 24.561] s from T0 and 909 ± 1/0.16 Hz. Each dynamical power spectra has the same lower threshold \({Z}_{1}^{2}\) statistic of 90% confidence level in \({\chi }_{2}^{2}\) distribution. b, Photon counts within [24.401, 24.561] s in different energy ranges (see Extended Data Table 1 for details). c, RMS fractional amplitudes at 909 Hz. Measurements from the \({Z}_{3}^{2}\) statistics are marked with blue error bars within the same time and energy interval as in b. The QPO is consistently observed across different detectors, each showing similar energy dependence and a peak RMS fractional amplitude around 27.2% (marked by red dashed lines), indicating that the QPO is captured independently by each detector.

Extended Data Fig. 2 Monte Carlo simulations to verify the 909-Hz signal in GRB 230307A.

a, The upper panel shows the GECAM-B light curve of GRB 230307A from [24.081, 24.881] s after T0, binned at 0.1 ms, with no notable pulses or data corruption detected around the QPO interval ([24.401, 24.561] s from T0). The median panel displays the WWZ spectrogram, where the red box marks the QPO interval and the associated frequency range (909 ± 1/0.16 Hz). The right panel shows the averaged WWZ power spectrum for the QPO interval. b, Distribution of simulated WWZ power from synthetic light curves generated based on the observed light curve within the QPO interval. The red curve approximates the probability density function using an F-distribution, while the purple vertical line indicates the observed power of the 909-Hz signal. c, Lomb-Scargle periodogram (LSP) of the light curve within the QPO interval. The red dotted, dashed, and solid lines represent the 3σ, 4σ, and 5σ false alarm levels, calculated using the Baluev method56.

Extended Data Fig. 3 Bayesian model fitting for the 909-Hz QPO in GRB 230307A.

a, Dynamical power spectra based on the Groth normalized power spectra30, mapped using overlapping 100-ms intervals with a step size of 1 ms. The white vertical lines mark the 100-ms time interval where the maximal power at 910 Hz was detected. b, Light curve of GRB 230307A. The red dashed vertical lines indicate the selected time interval ([24.451, 24.551] s from T0) used to generate the PDS. c, PDS with the best-fit QPO model. The gray shaded area indicates the red noise region within the 10-500 Hz range, showing no notable red noise excess. The red bands denote the 1σ, 2σ, and 3σ confidence intervals under the assumption of white noise only. The black curve represents the expected power spectrum for the model combining white noise and one QPO. d, Differential distribution of the Bayes factors, illustrating the ratio of Bayesian evidence for PDS models with and without a QPO. The Bayes factor \({{\mathcal{B}}}_{0}^{1}\) represents the ratio between the Bayesian evidence for the white noise plus one QPO model and the white noise model. All subsets were calculated using a 0.1-s segment length and a frequency range of 500-5,000 Hz. The gray histogram shows data from other short GRBs13, while the red histogram highlights the Bayes factors of the 909-Hz signal within [24.451, 24.551] s from T0 in GRB 230307A, comparable to those of GRB 931101B and GRB 97071113.

Extended Data Fig. 4 Coincidence between the 909-Hz signal’s detection interval and the transition to high-latitude emission.

a, Flux evolution of GRB 230307A based on GECAM data in 98-248 keV band. Blue error bars represent the time-resolved flux estimated from the best-fit spectral models, as detailed in ref. 16, including the corresponding time intervals and 1σ uncertainties. The red curve shows the best-fit smoothly broken power law with the corresponding 1σ error region. b, Evolution of temporal slopes. Blue points indicate the temporal slopes predicted by the ‘curvature effect’, and the red curve represents the slopes derived from the smoothly broken power law fitting in a. The vertical purple band marks the 909-Hz signal’s detection interval, which coincides with the transition point where the ‘curvature effect’ begins to dominate the observed gamma-ray flux.

Extended Data Fig. 5 Result of the blind search for periodicity in GRB 211211A.

We obtained candidates from 462,852 subsets of event data, partitioned from 8,935 segments, covering the light curve from [-0.016, 81.910] s from T0,211211A in the 5-975 keV range from detectors n2 and na onboard Fermi/GBM. a, b, c, d, e, Similar to Fig. 1, but for GRB 211211A. The maximum candidate power was observed at 546 Hz in b, corresponding to a signal within the time interval [14.880, 15.075] s from T0,211211A. This signal exhibited powers exceeding the threshold of Rfalse = 15.85 in the 500-549 Hz range, with a representative false alarm probability of approximately 31.09%, indicating that the signal is likely due to noise. Another signal within [50.914, 51.029] s from T0,211211A showed power exceeding the threshold at 935 and 936 Hz, but the representative false alarm probability of about 1.09% renders this signal insignificant.

Extended Data Fig. 6 Very strong red noise during GRB 211211A.

a, Light curve of GRB 211211A from Fermi/GBM in 5-975 keV. As shown in Extended Data Fig. 5, a signal yielding candidate powers exceeding the threshold within 500-549 Hz was observed. The corresponding time interval is marked with a red box. The inset shows a detailed view of this signal, revealing a very bright spike lasting about 1 ms. b, c, d, Light curves in the 5-20 keV range from Fermi/GBM detectors with incident angles less than 60°. The spike, observed around 14.977 s, was detected only by the NaI detector na (50.03°) and not by detector n2 (28.37°). Given the spike’s absence in detector n2 and its predominant contribution in the 5-20 keV range, it was excluded as a hyper flare from GRB 211211A. e, f, g, Groth normalized30 power spectra corresponding to the light curves in b, c, d. The grey shaded area denotes the 0-500 Hz frequency range, while the red shaded area highlights the 500-5,000 Hz region and the threshold power from Extended Data Fig. 5a. The bright spike detected by the detector na produced a series of red noise excesses extending up to 2,000 Hz, leading to the observation of extreme Rayleigh power during the search.

Extended Data Table 1 Energy Segmentation for the Time Interval [24.401, 24.561] s from T0 Using GECAM-B Data
Full size table
Extended Data Table 2 Results of PDS Model Fitting
Full size table

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Chen, RC., Zhang, BB., Wang, CW. et al. Evidence for a brief appearance of gamma-ray periodicity after a compact star merger. Nat Astron (2025). https://doi.org/10.1038/s41550-025-02649-w

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