XMM-Newton detection of hard X-ray emission from the nearby Type Ia-CSM SN 2026sqf

ATel #18146; F. Acero (FSLAC CNRS/IAC, AIM CEA/Saclay), A. Simongini (INAF-OAR, UniRoma2), M. de Bony de Lavergne (CPPM), R. Baer-Way (UVA), P. Chandra (NRAO), Y. Iwata (NAOJ), A. López-Oramas (IAC, La Laguna Univ.), K. Maeda (Kyoto Univ.), A. Nucara (INAF-IAPS, UniRoma2)
on 9 Nov 2026; 08:55 UT
Credential Certification: Fabio Acero (fabio.acero@cnrs.fr)

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We report the X-ray detection of the closest Type Ia-CSM supernova known to date, SN 2026sqf, in NGC 3310 (z = 0.003312; d ~ 19 Mpc), obtained as part of a dedicated multi-wavelength campaign. Observations with the EPIC instrument on board the XMM-Newton satellite were carried out on 2026 October 18 for 14 ks under Regular Proposal XMM/99379 (PI: Andrea Simongini). SN 2026sqf was detected in the 5-10 keV band, with a preliminary observed energy flux of ~1.5e-13 erg cm-2 s-1 (5-10 keV). To enable a direct flux comparison with the Chandra detection reported by Margutti+2026 (AstroNote 2026-275), we adopt the same thermal bremsstrahlung model, assuming a temperature of 10 keV and a line-of-sight absorption of N_H = 2e23 cm2. Under these assumptions, the flux extrapolated to the 0.3-10 keV band is ~1.8e-13 erg cm-2 s-1, comparable to the X-ray flux reported by Chandra on 2026-09-19. The spectral extraction region of SN 2026sqf suffers from contamination from nearby sources due to the XMM-Newton PSF. Further analysis is ongoing to refine the background correction and assess the presence of a signal at lower energies. SN 2026sqf is the closest Type Ia-CSM ever discovered (Rehemtulla+2026; AstroNote 2026-240) and the second detected in the X-ray band (Margutti+2026; AstroNote 2026-275). Multi-wavelength observations are ongoing and strongly encouraged. Based on observations obtained with XMM-Newton, an ESA science mission with instruments and contributions directly funded by ESA Member States and NASA.

A pre/post explosion XMM-Newton comparison is shown here.