TITLE:   GCN CIRCULAR
NUMBER:  33676
SUBJECT: GRB 221009A: Late-time JWST Observations and Detection of Supernova Emission
DATE:    23/04/23 02:40:59 GMT
FROM:    Peter K. Blanchard at Northwestern University <peter.blanchard@northwestern.edu>

P. K. Blanchard (Northwestern/CIERA), V. A. Villar (PSU), R. Chornock (UC Berkeley), H. Sears (Northwestern/CIERA), N. LeBaron (UC Berkeley), S. K. Yadavalli (PSU), T. Laskar (Utah), K. D. Alexander (Arizona), R. Margutti (UC Berkeley), E. Berger (Harvard/CfA), J. Barnes (UCSB), D. Siegel (U. Guelph/Perimeter), B. Metzger (Columbia and Flatiron/CCA), D. Kasen (UC Berkeley), Y. Cendes (Harvard/CfA), T. Eftekhari (Northwestern/CIERA), and J. Leja (PSU) report:

We obtained spectra at the position of the afterglow of GRB 221009A (Dichiara et al., GCN 32632; Lipunov et al., GCN 32634; Kennea & Williams, GCN 32635; Veres et al., GCN 32636; Bissaldi et al., GCN 32637) with JWST/NIRSpec under DDT program 2784 (P.I. Blanchard) starting at 2023 April 20 14:40 UT (193 observer-frame days after the burst). The spectra were taken with the G140M/F100LP and G235M/F170LP grating/filter combinations with an exposure time of 11,015 seconds in each setup. This yields a total wavelength coverage of about 1 - 3 microns.

We correct our combined G140M+G235M spectrum for Galactic extinction using the fitted extinction parameters found by Levan et al., ApJL, 946, L28 (2023). The spectrum significantly differs from a power-law continuum observed 13 days after the burst (observer frame; Levan et al., GCN 32821). This suggests that there is now significant contribution from the SN/host galaxy. We detect a broad emission line feature centered at ~1 micron (observer frame) consistent with the Ca II IR triplet from a SN, and prominent narrow, host galaxy emission lines. If confirmed by further analysis, this would represent the first identification of specific SN spectral features associated with GRB 221009A.

Further analysis is ongoing.

We thank STScI staff members Crystal Mannfolk, Leonardo Ubeda, Armin Rest and the entire JWST team for the successful implementation of this DDT program.