JWST finds a dust-hidden supernova that proves a gamma‑ray burst came from a massive star
A team used the James Webb Space Telescope to find a supernova hidden by dust at the location of gamma‑ray burst GRB 240825A. The burst had given mixed clues about its origin and earlier ground‑based searches did not see a clear supernova. The new JWST spectrum shows a point‑like source at the burst position whose features match a broad‑lined Type Ic supernova — the kind that comes from a collapsing massive star — so the burst’s origin is now firmly linked to a dying star.
The researchers observed the field with JWST’s Near Infrared Spectrograph (NIRSpec) 66.5 days after the burst, which is 40.1 days in the burst’s rest frame. They separated the supernova light from the light of the host galaxy by doing a pixel‑by‑pixel decomposition of the two‑dimensional spectrum and by fitting the host and transient at the same time. They also used the afterglow light from the near‑infrared to X‑ray bands to measure how much dust sits along the line of sight.
They found a compact source at the burst location whose broad spectral features look like those of SN 1998bw, a well‑studied example of a Type Ic broad‑lined supernova. Type Ic means the exploding star had lost its outer hydrogen and helium layers; “broad‑lined” means the explosion sent material out at very high speeds, which makes spectral lines wide. In the JWST spectrum the supernova supplies about 10–15% of the flux, while at the same epoch it would have contributed only about 1% of the light in a ground‑based optical image. The line of sight to the burst is dusty, with extinction A_V = 1.37 ± 0.08 magnitudes, and the data show tentative evidence for a 2175 Å dust feature.
The host galaxy is relatively bright and actively forming stars. From the data the authors estimate a stellar mass log(M★/M⊙) = 10.12 ± 0.05 and a star formation rate of 5.88 ± 1.60 solar masses per year. The gas‑phase metallicity is 12 + log(O/H) = 8.87 ± 0.04, which is above solar and higher than is typical for the hosts of collapsar (massive‑star) GRBs. These host properties show the burst occurred in a dusty, chemically enriched environment.