paper

SN 2020uem: A Possible Thermonuclear Explosion within A Dense Circumstellar Medium (I) The Nature of Type IIn/Ia-CSM SNe from Photometry and Spectroscopy

arXiv:2301.09901 · doi:10.3847/1538-4357/acb5ec

Abstract

We have performed intensive follow-up observations of a Type IIn/Ia-CSM SN (SN IIn/Ia-CSM), 2020uem, with photometry, spectroscopy, and polarimetry. In this paper, we report on the results of our observations focusing on optical/near-infrared (NIR) photometry and spectroscopy. The maximum V-band magnitude of SN 2020uem is over $- 19.5$ mag. The light curves decline slowly with a rate of $\sim 0.75 mag /100 days$ . In the late phase ( $≳ 300$ days), the light curves show accelerated decay ( $\sim 1.2 mag /100 days$ ). The optical spectra show prominent hydrogen emission lines and broad features possibly associated with Fe-peak elements. In addition, the $H I^\pm$ profile exhibits a narrow P-Cygni profile with the absorption minimum of $\sim 100 km s^{- 1}$ . SN 2020uem shows a higher $H I^\pm /H I^^{2}$ ratio ( $\sim 7$ ) than those of SNe IIn, which suggests a denser CSM. The NIR spectrum shows the Paschen and Brackett series with continuum excess in the H and Ks bands. We conclude that the NIR excess emission originates from newly-formed carbon dust. The dust mass ( $M_{d}$ ) and temperature ( $T_{d}$ ) are derived to be $(M_{d}, T_{d}) \sim (4 - 7 \times 1 0^{- 5} M_{⊙}, 1500 - 1600 K)$ . We discuss the differences and similarities between the observational properties of SNe IIn/Ia-CSM and those of other SNe Ia and interacting SNe. In particular, spectral features around $\sim 4650$ {\text Ã } and $\sim 5900$ {\text Ã } of SNe IIn/Ia-CSM are more suppressed than those of SNe Ia; these lines are possibly contributed, at least partly, by \ion{Mg}{1}] and \ion{Na}{1}, and may be suppressed by high ionization behind the reverse shock caused by the massive CSM.

22 pages, 15 figures, 3 tables. Accepted for publication in ApJ