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Arxiv: Late-time HST and JWST Observations of GRB 221009A: Evidence for a Break in the Light Curve at 50 Days Published: 12/3/2024 8:37:29 PM Updated: 12/3/2024 8:37:29 PM

Paper abstract: GRB 221009A is one of the brightest transients ever observed with the highestpeak gamma-ray flux for a gamma-ray burst (GRB). A type Ic-BL supernova (SN),SN 2022xiw, was definitively detected in late-time JWST spectroscopy (t = 195days, observer-frame). However, photometric studies have found SN 2022xiw to beless luminous (10-70%) than the canonical GRB-SN, SN 1998bw. We presentlate-time Hubble Space Telescope (HST)/WFC3 and JWST/NIRCam imaging of theafterglow and host galaxy of GRB 221009A at t ~ 185, 277, and 345 dayspost-trigger. Our joint archival ground, HST, and JWST light curve fits showstrong support for a break in the light curve decay slope at t = 50 +/- 10 days(observer-frame) and a supernova at 1.4^{+0.37}_{-0.40} \times theoptical/NIR flux of SN 1998bw. This break is consistent with an interpretationas a jet break when requiring slow-cooling electrons in a wind medium with theelectron energy spectral index, p > 2, and \nu_m < \nu_c. Our light curve andjoint HST/JWST spectral energy distribution (SED) also show evidence for thelate-time emergence of a bluer component in addition to the fading afterglowand supernova. We find consistency with the interpretations that this source iseither a young, massive, low-metallicity star cluster or a scattered light echoof the afterglow with a SED shape of f_{\nu} \propto \nu^{2.0\pm1.0}.