The Young and Nearby Normal Type Ia Supernova 2018gv: UV-optical Observations and the Earliest Spectropolarimetry
Final Published Version
Maund, Justyn R.
Brown, Peter. J.
Stevance, Heloise F.
Graham, Melissa. L.
Howell, D. Andrew
Jha, Saurabh W.
Sand, David. J.
Wheeler, J. Craig
AffiliationUniv Arizona, Steward Observ
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PublisherIOP PUBLISHING LTD
CitationYang, Y., Hoeflich, P., Baade, D., Maund, J. R., Wang, L., Brown, P. J., ... & Zhang, J. (2020). The young and nearby normal Type Ia supernova 2018gv: UV-optical observations and the earliest spectropolarimetry. The Astrophysical Journal, 902(1), 46.
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AbstractThe 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 theB-band maximum light, or similar to 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 (less than or similar to 0.2%) and moderate line polarization (0.30% 0.04% for the prominent Siii lambda 6355 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 similar to 100 days after the maximum light indicate that SN 2018gv is a normal SN Ia with similar spectrophotometric behavior to SN 2011fe.
VersionFinal published version