The optical light curve of GRB 221009A: the afterglow and the emerging supernova

M. D. Fulton*, S. J. Smartt, L. Rhodes, M. E. Huber, V. A. Villar, T. Moore, S. Srivastav, A. S. B. Schultz, K. C. Chambers, L. Izzo, J. Hjorth, T.-W. Chen, M. Nicholl, R. J. Foley, A. Rest, K. W. Smith, D. R. Young, S. A. Sim, J. Bright, Y. ZenatiT. de Boer, J. Bulger, J. Fairlamb, H. Gao, C.-C. Lin, T. Lowe, E. A. Magnier, I. A. Smith, R. Wainscoat, D. A. Coulter, D. O. Jones, C. D. Kilpatrick, P. McGill, E. Ramirez-Ruiz, K.-S. Lee, G. Narayan, V. Ramakrishnan, R. Ridden-Harper, A. Singh, Q. Wang, A. K. H. Kong, C.-C. Ngeow, Y.-C. Pan, S. Yang, K. W. Davis, A. L. Piro, C. Rojas-Bravo, J. Sommer, S. K. Yadavalli

*Corresponding author for this work

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We present extensive optical photometry of the afterglow of GRB 221009A. Our data cover 0.9–59.9 days from the time of Swift and Fermi gamma-ray burst (GRB) detections. Photometry in rizy-band filters was collected primarily with Pan-STARRS and supplemented by multiple 1–4 m imaging facilities. We analyzed the Swift X-ray data of the afterglow and found a single decline rate power law f(t) ∝ t−1.556±0.002 best describes the light curve. In addition to the high foreground Milky Way dust extinction along this line of sight, the data favor additional extinction to consistently model the optical to X-ray flux with optically thin synchrotron emission. We fit the X-ray-derived power law to the optical light curve and find good agreement with the measured data up to 5−6 days. Thereafter we find a flux excess in the riy bands that peaks in the observer frame at ∼20 days. This excess shares similar light-curve profiles to the Type Ic broad-lined supernovae SN 2016jca and SN 2017iuk once corrected for the GRB redshift of z = 0.151 and arbitrarily scaled. This may be representative of an SN emerging from the declining afterglow. We measure rest-frame absolute peak AB magnitudes of Mg = −19.8 ± 0.6 and Mr = − 19.4 ± 0.3 and Mz = −20.1 ± 0.3. If this is an SN component, then Bayesian modeling of the excess flux would imply explosion parameters of Mej = 7.1+2.4-1.7 M⊙, MNi = 1.0+0.6-0.4 M⊙, and vej =33,900+5900 -5700 km s−1, for the ejecta mass, nickel mass, and ejecta velocity respectively, inferring an explosion energy of Ekin ≃ 2.6–9.0 × 1052 erg.
Original languageEnglish
Article numberL22
Number of pages12
JournalThe Astrophysical Journal Letters
Issue number1
Publication statusPublished - 20 Mar 2023


  • 330
  • High-Energy Phenomena and Fundamental Physics


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