Journal
ASTROPHYSICAL JOURNAL
Volume 902, Issue 1, Pages -Publisher
IOP Publishing Ltd
DOI: 10.3847/1538-4357/aba759
Keywords
polarization; galaxies: individual (NGC 2525); supernovae: individual (SN 2018gv)
Categories
Funding
- ESO VLT at the Paranal Observatory [0102.D-0528]
- NASA [NAS5-26555]
- Benoziyo Prize Postdoctoral Fellowship
- NSF project Signatures of Type Ia Supernovae, New Physics and Cosmology [AST-1715133]
- Royal Society University Research Fellowship
- NSF [AST-1817099, HST-GO-14139.001-A, AST-1813825, AST-1313484, AST-1821987, 1821967]
- Mitchell Postdoctoral Fellowship
- University of Sheffield
- DIRAC Institute in the Department of Astronomy at the University of Washington
- National Natural Science Foundation of China (NSFC) [11178003, 11325313]
- NSFC [11773067, 11403096]
- Youth Innovation Promotion Association of the CAS [2018081]
- Western Light Youth Project of the CAS
- STFC [ST/R000964/1] Funding Source: UKRI
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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 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.
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