The nondetection of companion stars in SN Ia progenitor systems lends support to the notion of double-degenerate systems and explosions triggered by the merging of two white dwarfs. This very asymmetric process should lead to a conspicuous polarimetric signature. By contrast, observations consistently find very low continuum polarization as the signatures from the explosion process largely dominate over the pre-explosion configuration within several days. Critical information about the interaction of the ejecta with a companion and any circumstellar matter is encoded in the early polarization spectra. In this study, we obtain spectropolarimetry of SN 2018gv with the ESO Very Large Telescope at-13.6 days relative to the B-band maximum light, or ∼5 days after the estimated explosion-the earliest spectropolarimetric observations to date of any SN Ia. These early observations still show a low continuum polarization (≲0.2%) and moderate line polarization (0.30% ± 0.04% for the prominent Si ii λ6355 feature and 0.85% ± 0.04% for the high-velocity Ca component). The high degree of spherical symmetry implied by the low-line and continuum polarization at this early epoch is consistent with explosion models of delayed detonations and is inconsistent with the merger-induced explosion scenario. The dense UV and optical photometry and optical spectroscopy within the first ∼100 days after the maximum light indicate that SN 2018gv is a normal SN Ia with similar spectrophotometric behavior to SN 2011fe.
ASJC Scopus subject areas
- Astronomy and Astrophysics
- Space and Planetary Science
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Yang, Y. (Creator), Hoeflich, P. (Creator), Baade, D. (Creator), Maund, J. R. (Creator), Wang, L. (Creator), Brown, P. J. (Creator), Stevance, H. F. (Creator), Arcavi, I. (Creator), Burke, J. (Creator), Cikota, A. (Creator), Clocchiatti, A. (Creator), Gal-Yam, A. (Creator), Graham, M. L. (Creator), Hiramatsu, D. (Creator), Hosseinzadeh, G. (Creator), Howell, D. A. (Creator), Jha, S. W. (Creator), McCully, C. (Creator), Patat, F. (Creator), Sand, D. J. (Creator), Schulze, S. (Creator), Spyromilio, J. (Creator), Valenti, S. (Creator), Vinkó, J. (Contributor), Wang, X. (Creator), Wheeler, J. C. (Creator), Yaron, O. (Creator) & Zhang, J. (Creator), Centre de Donnees Strasbourg (CDS), 2022