[Paper Review] Multiband Photometry Evolution in the First Weeks of SN 2023ixf, a possible II-L Subtype Supernova

Giorgio Bianciardi, Armand Ciccarelli+9 more|arXiv (Cornell University)|Jul 10, 2023

Gamma-ray bursts and supernovae7 citations

TL;DR

The paper presents multi-observatory photometry of SN 2023ixf in multiple filters, showing a rapid rise to maximum and a linear, color-dependent decline, supporting its classification as Type II-L.

ABSTRACT

Multiband photometric observations and their evaluation to instrumental magnitudes were performed using standard Johnson-Cousins filters (B, V, Rc) as well r and g Sloan filters, and not standard ones (R, G, B, and Clear filters). These were recorded from 9 observatories and from the MicroObservatory Robotic Telescope Network. The results describe the rapid ascent towards the maximum (2.5 magnitudes about in five days in the B filter) and the slow decrease after the maximum (0.0425 +/- 0.02 magnitudes/day in the B filter). The results highlight the strong variation of the B-V colour indices during the first 50 days (from -0.20 +/- 0.02 to +0.85 +/- 0.02) and V-R (from 0 +/- 0.01 to +0.50 +/- 0.01) after the explosion, presumably corresponding to the cooling of the stellar photosphere. At 50 days after the explosion the magnitude decrease from the maximum was observed to continue where it faded by 2.5 magnitudes (B filter), thus we propose SN 2023ixf is a Type II, subtype L, supernova (SNe).

Motivation & Objective

• Characterize the early multiband light curve of SN 2023ixf across standard and non-standard filters.
• Quantify rise to maximum and subsequent decline rates in different photometric bands.
• Analyze color evolution (B-V, V-R) to interpret photospheric cooling.
• Assess whether the light-curve decline supports a II-L classification for SN 2023ixf.

Proposed method

• Collect mult observatory photometry using standard Johnson-Cousins B, V, Rc, and Sloan r, g as well as non-standard tri-color filters.
• Perform aperture photometry with MaximDL and use a common reference star (TYC 3852-1108-1) for magnitude calibration where possible.
• Estimate uncertainties (0.002–0.06 mag; mean ~0.02–0.007 mag) across observatories.
• Analyze light-curve rise to maximum and subsequent declines with band-dependent slopes.
• Compute color indices B-V and V-R and fit their evolution over the first ~50 days.

Figure 1: SN 2023ixf occurred in a spiral arm of the Pinwheel Galaxy. This wide-field image was made by one of us on the night of 2023/05/28. The characteristic cyan colour of the supernova near the maximum is well-defined. Reference star is indicated. Image credit: Giuseppe Conzo, UAI Remote Telesc

Experimental results

Research questions

• RQ1 What are the rise and decline characteristics of SN 2023ixf in multiple photometric bands during the first 50 days after explosion?
• RQ2 How do color indices (B-V, V-R) evolve in the early phases, and what do they imply about the photospheric temperature evolution?
• RQ3 Does the photometric behavior align with an II-L (linear) Type II supernova classification?
• RQ4 How consistent are measurements from heterogeneous instruments and filter sets in constructing the light curve?

Key findings

• SN 2023ixf shows a rapid rise to maximum of about 2.5 magnitudes in the B band over five days.
• Post-maximum decline in the B band is linear with a slope of 0.0425 ± 0.02 mag/day.
• The G band shows an earlier onset of decline with a slope of 0.022 ± 0.01 mag/day; R band declines at 0.0187 ± 0.007 mag/day.
• 50 days after explosion, the B-band decline reaches 2.5 magnitudes from maximum.
• B-V varies from -0.20 ± 0.02 to +0.85 ± 0.02, and V-R from 0 ± 0.01 to +0.50 ± 0.01, indicating cooling of the photosphere.
• The observed light-curve behavior supports classifying SN 2023ixf as Type II-L (linear decline) rather than II-P (plateau).

Figure 2: This image at a higher resolution than Figure 1 made by one of us shows that SN 2023ixf occurred in a region rich in gas and near several star-forming regions. Image credit: Z. Organić, Orbanić Explorer Observatory.