학술논문
The Young and Nearby Normal Type Ia Supernova 2018gv: UV-optical Observations and the Earliest Spectropolarimetry
Document Type
article
Author
Yang, Y; Hoeflich, P; Baade, D; Maund, JR; Wang, L; Brown, PJ; Stevance, HF; Arcavi, I; Burke, J; Cikota, A; Clocchiatti, A; Gal-Yam, A; Graham, ML; Hiramatsu, D; Hosseinzadeh, G; Howell, DA; Jha, SW; McCully, C; Patat, F; Sand, DJ; Schulze, S; Spyromilio, J; Valenti, S; Vinkó, J; Wang, X; Wheeler, JC; Yaron, O; Zhang, J
Source
Astrophysical Journal. 902(1)
Subject
Language
Abstract
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.