Discovered by ATLAS on 2026-04-22 07:31:46 in NGC3437 at 18.09 mag (Orange ATLAS) (TNS N°300956) (https://www.wis-tns.org/object/2026kie) classified by Schmidt et al. as a SN Ib (TNS Classification Report 2026-1791), then reclassified by ePESSTO+ as a SN Ic event (TNS AstroNote 2026-126), RAPAS ProAm network monitors the rise of SN 2026kie from 2026-04-23 up to now and will follow it later on. We provide multi-band photometry and a spectral energy distribution (SED). During this period, 3 telescopes located in France, using the set of RAPAS G, Gbp and Grp filters meeting the three Gaia G, Gbp and Grp photometric band specifications, and additional 3 telescopes in France and Chile using other filters collected around 25 measurements in 1, 2 or the 3 Gaia bands through the two weeks following the discovery. The photometric consistency was ensured by reducing each frame using RAPAS filters with the respective Gaia DR3 reference catalog for G, Gbp and Grp bands.
Since SN 2026kie is located on the disk of its host galaxy NGC 3437, aperture photometry is contaminated by the underlying galaxy light. Several reported magnitudes are therefore derived from template subtraction: pre-explosion reference images from the ZTF DR7 survey (g-band for Gbp, r-band for G, i-band for Grp) are convolved to match the science image PSF and subtracted using HOTPANTS (Becker 2015), isolating the supernova flux. This processing is performed automatically by STDWeb, built on the STDPipe pipeline (Karpov 2021 for GRANDMA project). We will try to improve the consistency of all the data later on, in improving the processing of these wide range of filters and processing used here.
The multi-band light curve shows the supernova brightening at approximately −0.1 mag/day in G-band (template subtraction) between April 25 and 27.
On the 2026-05-04 the light curves show a peak at 16.4 G magnitude, 15.9 Gbp magnitude and 15.5 Grp magnitude.
The Color Index Gbp−Grp increased from -0.4 up to 0.5, indicating an equivalent temperature decrease while the supernova is approaching maximum light. Then the Color Index increased to 1.0 showing the SN is cooling down while the SN is going through the peak then starting to fade. Note: the April 24 measurements in G and Grp bands have S/N < 3 in template subtraction and should be treated with caution.
The Olivier Garde 2SPOT spectrum was obtained on 2026-04-23 with one of the C2PU 1m telescopes equipped with a 50µm slit on LISA spectrograph. The R300 SED displays low P Cygni features. Hα and [SII] emission lines from the underlying host galaxy are also present.
Detailed light curves and data are presented on the RAPAS web page and Astro-COLIBRI web page on the following links :
https://rapas.imcce.fr/SN2026kie-lightcurve.jpg
https://rapas.imcce.fr/SN2026kie-mag-vs-bp-rp-index.jpg
https://rapas.imcce.fr/SN2026kie_RAPAS.csv
https://rapas.imcce.fr/SN2026kie-SED-20260423.jpg
Further details and the full dataset are accessible to registered users of the RAPAS Spreadsheets platform.
Acknowledgements :
RAPAS ( https://gemini.obspm.fr/20220101-rapas/ ) is a ProAm collaboration created by T. Midavaine (SAF), W. Thuillot (LTE, Obs. de Paris-PSL) and M. Dennefeld (IAP/CNRS and Sorbonne Univ.) and funded by the Paris Observatory under API ProAm of the Scientific Council. It aims at homogenizing observing procedures and filters, and is delivering to a network of amateur observatories a set of 3 filters which have been chosen to meet the Gaia G, Gbp and Grp spectral bands. This network produces data on astrophysical alerts delivered by various Alert systems (Gaia Alerts, Atlas, ZTF, etc…) and collected by Astro-COLIBRI ( https://astro-colibri.science ). This network is similarly progressing towards an homogeneous spectroscopic equipment to deliver SED.
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