Late-time HST and JWST Observations of GRB 221009A: Evidence for a Break in the Light Curve at 50 days

Late-time HST and JWST Observations of GRB 221009A: Evidence for a Break in the Light Curve at 50 days

GRB 221009A is one of the brightest transients ever observed, with the highest peak 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 = 195 days, observer frame). However, photometric studies have found S...

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Main Authors: Huei Sears, Ryan Chornock, Peter K. Blanchard, Raffaella Margutti, V. Ashley Villar, Justin Pierel, Patrick J. Vallely, Kate D. Alexander, Edo Berger, Tarraneh Eftekhari, Wynn V. Jacobson-Galán, Tanmoy Laskar, Natalie LeBaron, Brian D. Metzger, Dan Milisavljevic
Format: Article
Language:English
Published: IOP Publishing 2025-01-01
Series:The Astrophysical Journal
Subjects:
Gamma-ray bursts
Core-collapse supernovae
Supernovae
High energy astrophysics
HST photometry
Hubble Space Telescope
Online Access:https://doi.org/10.3847/1538-4357/adc306
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Summary:GRB 221009A is one of the brightest transients ever observed, with the highest peak 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 = 195 days, observer frame). However, photometric studies have found SN 2022xiw to be less luminous (10%−70%) than the canonical GRB-SN, SN 1998bw. We present late-time Hubble Space Telescope (HST)/WFC3 and JWST/NIRCam imaging of the afterglow and host galaxy of GRB 221009A at t ∼185, 277, and 345 days post-trigger. Our joint archival ground, HST, and JWST light-curve fits show strong support for a break in the light-curve decay slope at t = 50 ± 10 days (observer frame) and a SN at <1.5× the optical/near-IR flux of SN 1998bw. This break is consistent with an interpretation as a jet break when requiring slow-cooling electrons in a wind medium with an electron energy spectral index p > 2 and ν _m < ν _c . Our light curves and joint HST/JWST spectral energy distribution (SED) also show evidence for the late-time emergence of a bluer component in addition to the fading afterglow and SN. We find consistency with the interpretations that this source is either a young, massive, low-metallicity star cluster or a scattered-light echo of the afterglow with a SED shape of f _ν ∝ ν ^2.0±1.0 .
ISSN:1538-4357

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