A1 Refereed original research article in a scientific journal
The Redshift of GRB 190829A/SN 2019oyw: A Case Study of GRB-SN Evolution
Authors: Bhirombhakdi, Kornpob; Fruchter, Andrew S.; Levan, Andrew J.; Pian, Elena; Mazzali, Paolo; Izzo, Luca; Kangas, Tuomas; Benetti, Stefano; Medler, Kyle; Tanvir, Nial
Publisher: IOP Publishing Ltd
Publishing place: BRISTOL
Publication year: 2024
Journal: Astrophysical Journal
Journal name in source: ASTROPHYSICAL JOURNAL
Journal acronym: ASTROPHYS J
Article number: 256
Volume: 977
Issue: 2
Number of pages: 16
ISSN: 0004-637X
eISSN: 1538-4357
DOI: https://doi.org/10.3847/1538-4357/ad8dd8
Web address : https://doi.org/10.3847/1538-4357/ad8dd8
Self-archived copy’s web address: https://research.utu.fi/converis/portal/detail/Publication/478110704
The nearby long gamma-ray burst (GRB) 190829A was observed using the Hubble Space Telescope/Wide Field Camera 3/infrared grisms about four weeks to 500 days after the burst. We find the spectral features of its associated supernova, SN 2019oyw, are redshifted by several thousand km s-1 compared to the redshift of the large spiral galaxy on which it is superposed. This velocity offset is seen in several features but most clearly in Ca ii near-infrared triplet lambda lambda 8498, 8542, 8662 (CaIR3). We also analyze Very Large Telescope/FOcal Reducer and low dispersion Spectrograph and X-shooter spectra of the supernova (SN) and find strong evolution with time of its P-Cygni features of CaIR3 from the blue to the red. However, comparison with a large sample of Type Ic-BL and Ic SNe shows no other object with the CaIR3 line as red as that of SN 2019oyw were it at the z = 0.0785 redshift of the disk galaxy. This implies that SN 2019oyw is either a highly unusual SN or is moving rapidly with respect to its apparent host. Indeed, using CaIR3 we find the redshift of SN 2019oyw is 0.0944 <= z <= 0.1156. The GRB-SN is superposed on a particularly dusty region of the massive spiral galaxy; therefore, while we see no sign of a small host galaxy behind the spiral, it could be obscured. Our work provides a surprising result on the origins of GRB 190829A, as well as insights into the time evolution of GRB-SNe spectra and a method for directly determining the redshift of a GRB-SN using the evolution of strong spectral features such as CaIR3.
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Funding information in the publication:
This research is based on observations made with NASA/ESA Hubble Space Telescope obtained from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. The HST observations presented here were taken under General Observer(GO) Programs 15089, 15510, 16042, and 16320. Support for K.B. was provided through grants associated with GO Programs 15510, 16042, and 16320 from the STScI under NASA contract NAS5-26555.
