Two years of shock interaction tracing three phases of evolution: the explosion of a Type IIn supernova, SN 2019vxm

Gitika Rameshan, Rishabh Singh Teja, D. K. Sahu, G. C. Anupama, Masayuki Yamanaka, Keiichi Maeda, Tatsuya Nakaoka, Sota Goto, Brajesh Kumar, Avinash Singh, Miho Kawabata, Koji S. Kawabata, Kenta Taguchi

First listed 2026-06-25 | Last updated 2026-06-24

Abstract

We present multi-wavelength photometric and optical spectroscopic observations of the long-lived interacting supernova SN 2019vxm, spanning more than two years after the explosion. SN 2019vxm is a slowly rising (rise time ~ 45.9 days in the R-band), slowly declining supernova reaching an R-band peak absolute magnitude of ~-20.3 mag. The SN light curve post-maximum shows a shallow decline, followed by a secondary, steeper decline in the optical (0.01 mag/day), with late-time IR brightening. The total radiated luminosity is 5x10^50 erg, placing it among the energetic class of its type. We estimated a CSM mass of 3-8 M_sun through light-curve modeling (independent of the CSM density profile) and by comparison with theoretical models. We estimate a minimum ejecta mass of ~ 3.88 M_sun from the broad H-alpha component, consistent with the ejecta mass obtained from the light curve models. The solely interaction-dominated initial epochs are later accompanied by photon-scattering signatures, leading to asymmetric line profiles with symmetric wings. The late phase, characterized by enhanced brightness at longer wavelengths and a stronger asymmetric line profile with the red side flux strongly suppressed, indicates the influence of pre-existing or newly formed dust with temperatures ~ 1500 K at ~4x10^16 cm. Even in the late phases, no nebular lines are present in the spectra, indicating dense or obscured ejecta.

Short digest

This paper follows the long-lived Type IIn SN 2019vxm for more than two years with UV-optical-NIR photometry and optical spectroscopy, showing a slow 45.9-day rise, a luminous peak at M_R about -20.3, and a total radiated energy of about 5x10^50 erg. Light-curve modeling and the broad H-alpha component both imply a massive interaction-powered event, with roughly 3-8 M_sun of circumstellar material and a minimum ejecta mass of about 3.88 M_sun. The spectroscopy resolves three phases: an initially interaction-dominated stage, a middle phase where photon scattering produces asymmetric Balmer cores with symmetric wings, and a late phase with IR brightening and strong suppression of red-side flux that points to dust at about 1500 K and around 4x10^16 cm. SN 2019vxm therefore stands out as an energetic, long-duration interacting supernova in which dense CSM interaction and dust obscuration continue to hide nebular ejecta signatures even at late times.

Key figures to inspect

• Figure 2. Use this as the main observational overview figure. It establishes the unusually slow rise, the shallow early decline followed by a steeper optical fading, and the broad UV-to-NIR coverage that makes the later IR excess and long interaction timescale immediately visible.
• Figure 3. This is one of the clearest summary figures for the paper’s late-time physics. The pseudo-bolometric decomposition and the optical-to-IR crossover directly support the claim that the event transitions into an IR-bright, dust-affected phase rather than remaining a purely optical interaction-powered transient.
• Figure 6. This figure should be included because it carries the paper’s quantitative interaction modeling. It shows how the fitted light-curve model reproduces the long-lived emission and underpins the inferred massive CSM needed to power SN 2019vxm.
• Figure 8. This is the key spectroscopic evolution figure for the three-phase story in the title and abstract. The progression from early symmetric Balmer profiles to profiles with symmetric wings and then to strong red-side suppression is the most direct visual evidence for the shift from pure interaction to scattering and finally to dust-affected line formation.
• Figure 12. Include this later diagnostic figure because it quantifies the asymmetry instead of only showing it qualitatively. The mirrored H-alpha profiles, blue-to-red flux ratio, and Balmer decrement evolution are central for arguing that the late-time line shapes are not a minor fluctuation but a sustained physical change tied to obscuration and dense post-shock conditions.