English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Plus monthly

Global: Zendy Tools annual

Global: Zendy Tools monthly

Global: Zendy Free Plan

We present our spectropolarimetric observations of SN 2017egm, a Type Isuperluminous supernova (SLSN-I) in a nearby galaxy NGC 3191, with Subarutelescope at 185.0 days after the g-band maximum light. This is the firstspectropolarimetric observation for SLSNe at late phases. We find that thedegree of the polarization in the late phase significantly changes from thatmeasured at the earlier phase. The spectrum at the late phase shows a strong Caemission line and therefore we reliably estimate the interstellar polarizationcomponent assuming that the emission line is intrinsically unpolarized. Bysubtracting the estimated interstellar polarization, we find that the intrinsicpolarization at the early phase is only ~ 0.2 %, which indicates an almostspherical photosphere, with an axial ratio ~ 1.05. The intrinsic polarizationat the late phase increases to ~ 0.8 %, which corresponds to the photospherewith an axial ratio 1.2. A nearly constant position angle of the polarizationsuggests the inner ejecta are almost axisymmetric. By these observations, weconclude that the inner ejecta are more aspherical than the outer ejecta. Itmay suggest the presence of a central energy source producing aspherical innerejecta.

Late-Phase Spectropolarimetric Observations of Superluminous Supernova SN 2017egm to Probe the Geometry of the Inner Ejecta