A COLIBRI Photometric Study of SN 2025bvm: A Normal, Slowly Declining Type Ia Supernova

TL;DR

This study presents 121 days of multi-band photometry of SN 2025bvm with the COLIBRI telescope, applying multiple light-curve fitters to derive key parameters. It finds a slow-declining, normal Ia with $Delta m15(B)=0.867±0.051$ and $M_B=-19.13±0.40$ mag at $d=70$ Mpc, along with a quasi-bolometric peak luminosity of $L_{peak}≈6.91×10^{42}$ erg s^-1 and $M_{Ni}≈0.34 M_sun$; the host reddening is $E(B-V)_{total}≈0.328±0.030$ mag, and a prominent i'-band secondary maximum further supports a massive ejecta. The results position SN 2025bvm as a normal Ia at the high-ejecta-mass end, providing constraints on explosion physics and progenitor scenarios. Overall, the work demonstrates the value of dense, multi-band photometry for robust SN Ia classification and ejecta-property inferences.

Abstract

We present 121 days of multi-band (\Bband, \gband, \rband, \iband) optical photometry of the Type Ia supernova SN 2025bvm, obtained with the COLIBRI telescope at OAN-SPM. The light curves show a photometric decline of $Δm_{15}(B) = 0.867 \pm 0.051$~mag, characteristic of a slow-declining Type Ia supernova. After correcting for host galaxy extinction ($E(B-V)_{host} = 0.308 \pm 0.030$~mag) and adopting a distance of 70~Mpc, we derive a peak absolute magnitude of $M_B = -19.13 \pm 0.40$~mag. This luminosity is fully consistent with its slow decline rate, placing SN 2025bvm within the population of normal Type Ia supernovae. We conclude that SN 2025bvm is a normal Type Ia supernova, whose photometric properties, such as a slow late-time decline and a prominent \iband-band secondary maximum, suggest an explosion that resulted in a particularly massive ejecta.

Figures (9)

• Figure 1: Field of view from the COLIBRI telescope observations. Left: The full field, identifying supernova SN 2025bvm (7) in its host galaxy NGC 4156 (6), the nearby galaxy NGC 4151 (1), and the standard stars used for photometric calibration (listed in Table \ref{['tab:standarStars']}). Right: A $5'\times5'$ cutout of the $\mathrm{r'}$-band image, centered on the host galaxy. The position of SN 2025bvm is marked with red crosshairs. In both panels, North is up and East is to the left.
• Figure 2: The observed $\mathrm{B}$, $\mathrm{g'}$, $\mathrm{r'}$, and $\mathrm{i'}$-band light curves of SN 2025bvm from the COLIBRI telescope. SNooPy2 model fits to the multi-band light curves of SN 2025bvm to determine the peak parameters. The solid grey line shows the best-fit template model in each band. The red square marks the resulting time ($t_{max}$) and magnitude ($m_{max}$) of the peak.
• Figure 3: Corner plot showing the posterior probability distributions for the key $\mathrm{B}$-band light-curve parameters of SN 2025bvm, as derived from the SNooPy2 fit. The diagonal panels show the probability distribution for each parameter: the time of maximum ($t_{max}(B)$), the apparent magnitude at maximum ($m_{max}(B)$), and the decline rate ($\Delta m_{15}(B)$). The off-diagonal panels show the covariances between parameter pairs. The contours represent the 1, 2, and 3-$\sigma$ confidence levels.
• Figure 4: Intrinsic color evolution of SN 2025bvm (black points) compared to a sample of normal Type Ia supernovae. From left to right, the panels show the evolution of the $(g-r)$, $(g-i)$, and $(r-i)$ colors. All supernovae shown have been corrected for their total line-of-sight extinction (both Galactic and host galaxy). The good morphological agreement of SN 2025bvm with the comparison sample across all three colors supports our derived reddening value and confirms its nature as a normal Type Ia supernova.
• Figure 5: The intrinsic light curves of SN 2025bvm after applying the full extinction correction. For visualization purposes, the light curves have been shifted vertically by the offsets listed in the legend. The correction reveals the intrinsically blue nature of the supernova at maximum light, with the $\mathrm{B}$-band peak being significantly brighter than in the redder bands.