Type IIn supernovae (SNe) resembling SN 2009ip (09ip-like SNe) originate from
the interaction between circumstellar material (CSM) and the ejecta. This
subclass not only shares similar observational properties around the maximum,
but is commonly characterized by a long duration precursor before its maximum.
Investigating the observed properties of the precursor provides constraints on
the mass-loss history of the progenitor.We present observational data of SN
2023vbg, a 09ip-like type IIn SN that displayed unique observational properties
compared to other 09ip-like SNe. SN 2023vbg showed a long-duration precursor at
$M_g\sim-14$ mag lasting for $\sim100$ days, followed by a bright bump at
$M_g\sim-17$ mag at 12-25 days before the maximum. The luminosity of the
precursor is similar to those of other 09ip-like SNe, but the bright bump has
not been observed in other cases.After reaching the peak luminosity, the light
curve exhibited a peculiar smooth decline.While the H$\alpha$ profile displays
two velocity components ($\sim 500$ et $3000\ \mathrm{km\ s^{-1}}$), a broad
component observed in other 09ip-like SNe was not detected. We suggest that
these properties are explained by the difference in the CSM structure as
compared to other 09ip-like SNe; SN 2023vbg had an inner denser CSM component,
as well as generally smooth CSM density distribution in a more extended scale,
than in the others. Such diversity of CSM likely reflects the diversity of
pre-SN outbursts, which in turn may mirror the range of evolutionary pathways
in the final stages of the progenitors.

Cet article explore les excursions dans le temps et leurs implications.

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