Rare Calcium-Rich Supernova Offers New Clues to Stellar Explosions
Astronomers analyzed a peculiar supernova that defies easy classification, revealing it may have erupted from a compact stellar remnant surrounded by recently shed material. The findings help refine models for predicting extreme stellar explosions, which inform space weather monitoring and our understanding of cosmic element creation.
Originaltitel: The Double-peaked Calcium-strong SN 2025coe: Progenitor Constraints from Early Interaction and Ejecta Asymmetries
Abstract Supernova (SN) 2025coe at a distance of ∼25 Mpc is the second-closest calcium-strong transient. It was discovered at a large projected offset of ∼34 kpc from its potential host galaxy NGC 3277. Multiband photometry of SN 2025coe indicates the presence of two peaks at day ∼2 and day ∼11 after explosion. Modeling the bolometric light curve, we find that the first peak can be reproduced either by shock cooling of a compact envelope ( R env ≈6–40 R ⊙ ; M env ≈0.1–0.2 M ⊙ ) or by interaction with close-in circumstellar material (CSM; R CSM ≲ 6 × 10 14 cm), or a combination of both. The second peak is dominated by radioactive decay of 56 Ni ( M ej ≈ 0.4–0.5 M ⊙ ; <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>M</mml:mi> </mml:mrow> <mml:mrow> <mml:msup> <mml:mrow/> <mml:mrow> <mml:mn>56</mml:mn> </mml:mrow> </mml:msup> <mml:mi mathvariant="normal">Ni</mml:mi> </mml:mrow> </mml:msub> <mml:mo>≈</mml:mo> <mml:mn>1.4</mml:mn> <mml:mo>×</mml:mo> <mml:mn>1</mml:mn> <mml:msup> <mml:mrow> <mml:mn>0</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>2</mml:mn> </mml:mrow> </mml:msup> </mml:math> M ⊙ ). SN 2025coe rapidly evolves from the photospheric phase dominated by He I P Cygni profiles to nebular phase spectra dominated by strong [Ca ii ] λλ 7291, 7323 and weak [O i ] λλ 6300, 6364 emission lines. Simultaneous line profile modeling of [Ca ii ] and [O i ] at nebular phases shows that an asymmetric core-collapse explosion of a low-mass (≲3.3 M ⊙ ) He-core progenitor can explain the observed line profiles. Alternatively, lack of local star formation at the site of the SN explosion combined with a low ejecta mass is also consistent with a thermonuclear explosion due to a low-mass hybrid He-C/O white dwarf +C/O white dwarf merger.