2025/02/24 by W. B. Hoogendam, Hoogendam, W. B., D. O. Jones +76 · 2 voices · 4 citations
Physics and Astronomy · #Gamma-ray bursts and supernovae
paper · pdf · doi:10.33232/001c.143462
We present optical-to-near-infrared (NIR) photometry and spectroscopy of the Type Ia supernova (SN~Ia) 2024epr, including NIR spectra observed within two days of first light. The early-time optical spectra show strong, high-velocity Ca and Si features near rarely-observed velocities at <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:mn>0.1</mml:mn> </mml:math> c, and the NIR spectra show a “knee.’’ Despite early-time, high-velocity features, SN~2024epr evolves into a normal SN~Ia, albeit with stronger peak-light Ca absorption than other SNe~Ia with the same light curve shape. Although we infer a normal decline rate, <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:mrow> <mml:mi>Δ</mml:mi> <mml:msub> <mml:mi>m</mml:mi> <mml:mn>15</mml:mn> </mml:msub> <mml:mrow> <mml:mo stretchy="true" form="prefix">(</mml:mo> <mml:mi>B</mml:mi> <mml:mo stretchy="true" form="postfix">)</mml:mo> </mml:mrow> <mml:mo>=</mml:mo> <mml:mn>1.09</mml:mn> <mml:mo>±</mml:mo> <mml:mn>0.12</mml:mn> </mml:mrow> </mml:math> ~mag, from the light-curve rise, SN~2024epr is a Branch”cool’’ object and has red early-time colors ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:mrow> <mml:mi>g</mml:mi> <mml:mo>−</mml:mo> <mml:mi>r</mml:mi> <mml:mo>≈</mml:mo> <mml:mn>0.15</mml:mn> </mml:mrow> </mml:math> ~mag at <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>10</mml:mn> </mml:mrow> </mml:math> ~days). The high velocities point to a density enhancement in the outer layers of the explosion, predicted by some models, but thick-shell He-detonation models do not match the smoothly rising light curve or apparent lack of He in our early-time NIR spectra. No current models (e.g., delayed detonation or thin He shell double detonation) appear to reproduce all observed properties, particularly the unusual early-time colors. Such constraints are only possible for SN~2024epr from the earliest optical and NIR observations, highlighting their importance for constraining SN~Ia models. Finally, we identify several literature SNe~Ia with intermediate mass elements at <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:mrow> <mml:mn>30</mml:mn> <mml:mspace width="0.167em"/> <mml:mn>000</mml:mn> <mml:mspace width="0.222em"/> <mml:mi>k</mml:mi> <mml:mi>m</mml:mi> <mml:mspace width="0.222em"/> <mml:mi>s</mml:mi> </mml:mrow> </mml:math> -1 within days after the explosion that evolve into otherwise normal SNe~Ia at peak light, suggesting the early-time spectra of SNe~Ia may hide a broad diversity of observational characteristics.