The Optical Light Curve of GRB 221009A: The Afterglow and the Emerging Supernova

[摘要] 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 inrizy -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 lawf ( 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 theriybands 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 ofz= 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 ofM _g = −19.8 ± 0.6 andM _r = − 19.4 ± 0.3 andM _z = −20.1 ± 0.3. If this is an SN component, then Bayesian modeling of the excess flux would imply explosion parameters of {M}_{mathrm{ej}}={7.1}_{-1.7}^{+2.4}M _⊙, {M}_{mathrm{Ni}}={1.0}_{-0.4}^{+0.6}M _⊙, and {v}_{mathrm{ej}}={{rm{33,900}}}_{-5700}^{+5900} km s⁻¹, for the ejecta mass, nickel mass, and ejecta velocity respectively, inferring an explosion energy ofE _kin ≃ 2.6–9.0×10⁵² erg.