Evidence for a luminosity–decay correlation in GRB GeV light curves

K R Hinds*, S R Oates*, M Nicholl, J Patel, N Omodei, B Gompertz, J L Racusin, G Ryan

*Corresponding author for this work

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Abstract

Correlations between intrinsic properties of gamma-ray burst (GRB) light curves provide clues to the nature of the central engine, the jet, and a possible means to standardize GRBs for cosmological use. Here, we report on the discovery of a correlation between the intrinsic early-time luminosity, LG,10 s, measured at rest frame 10 s, and the average decay rate measured from rest frame 10 s onward, αG,avg>10 s, in a sample of 13 Fermi Large Area Telescope long GRB light curves. We note that our selection criteria, in particular the requirement for a redshift to construct luminosity light curves, naturally limits our sample to energetic GRBs. A Spearman’s rank correlation gives a coefficient of –0.74, corresponding to a confidence level of 99.6 per cent, indicating that brighter afterglows decay faster than less luminous ones. Assuming a linear relation with log(LG,10s), we find αG,avg>10 s= −0.31+0.12 −0.09 log(LG,10s) + 14.43+4.55 −5.97. The slope of −0.31 is consistent at 1σ with previously identified correlations in the optical/ultraviolet and X-ray light curves. We speculate that differences in the rate at which energy is released by the central engine or differences in observer viewing angle may be responsible for the correlation.
Original languageEnglish
Pages (from-to)3400–3406
Number of pages7
JournalMonthly Notices of the Royal Astronomical Society
Volume526
Issue number3
Early online date22 Sept 2023
DOIs
Publication statusPublished - Dec 2023

Bibliographical note

Acknowledgments:
The Fermi LAT Collaboration acknowledge generous ongoing support from a number of agencies and institutes that have supported both the development and the operation of the Large Area Telescope (LAT) as well as scientific data analysis. These include the National Aeronautics and Space Administration and the Department of Energy in the United States, the Commissariat à l’Energie Atomique and the Centre National de la Recherche Scientifique/Institut National de Physique Nucléaire et de Physique des Particules in France, the Agenzia Spaziale Italiana and the Istituto Nazionale di Fisica Nucleare in Italy, the Ministry of Education, Culture, Sports, Science and Technology (MEXT), High Energy Accelerator Research Organization (KEK), and Japan Aerospace Exploration Agency (JAXA) in Japan, and the K. A. Wallenberg Foundation, the Swedish Research Council, and the Swedish National Space Board in Sweden. Additional support for science analysis during the operations phase is gratefully acknowledged from the Istituto Nazionale di Astrofisica in Italy and the Centre National d’Études Spatiales in France. This work performed in part under DOE Contract DE-AC02-76SF00515. KRH would like to thank the Science and Technology Facilities Council (STFC) and Faculty of Engineering and Technology (FET) at Liverpool John Moores University (LJMU) for his studentship. MN is supported by the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement No. 948381) and by UK Space Agency Grant No. ST/Y000692/1.

Keywords

  • (transients:) gamma-ray bursts

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