Early Shock-Cooling Observations and Progenitor Constraints of Type IIb SN 2024uwq

Bhagya M. Subrayan, David J. Sand, K. Azalee Bostroem, Saurabh W. Jha, Aravind P. Ravi, Michaela Schwab, Jennifer E. Andrews, Griffin Hosseinzadeh, Stefano Valenti, Yize Dong, Jeniveve Pearson, Manisha Shrestha, Lindsey A. Kwok, Emily Hoang, Jeonghee Rho, Seong Hyun Park, Sung-Chul Yoon, T. R. Geball, Joshua Haislip, Daryl Janzen, Vladimir Kouprianov, Darshana Mehta, Nicolás Meza Retamal, Daniel E. Reichart, Moira Andrews, Joseph Farah, Megan Newsome, D. Andrew Howell, Curtis McCully

First listed 2025-05-05 | Last updated 2025-05-05

Abstract

We present early multi-wavelength photometric and spectroscopic observations of the Type IIb supernova SN 2024uwq, capturing its shock-cooling emission phase and double-peaked light curve evolution. Early spectra reveal broad H-alpha (v ~ 15,500 km s$^{-1}$) and He I P-Cygni profiles of similar strengths. Over time the He I lines increase in strength while the H-alpha decreases, consistent with a hydrogen envelope ($M_{env}$ = 0.7 - 1.35 $M_\odot$ ) overlying helium-rich ejecta. Analytic modeling of early shock cooling emission and bolometric light analysis constrains the progenitor to a partially stripped star with radius R = 10 - 60 $R_\odot$, consistent with a blue/yellow supergiant with an initial ZAMS mass of 12 - 20 $M_\odot$ , likely stripped via binary interaction. SN 2024uwq occupies a transitional position between compact and extended Type IIb supernovae, highlighting the role of binary mass-transfer efficiency in shaping a continuum of stripped-envelope progenitors. Our results underscore the importance of both early UV/optical observations to characterize shock breakout signatures critical to map the diversity in evolutionary pathways of massive stars. Upcoming time domain surveys including Rubin Observatory's LSST and UV missions like ULTRASAT and UVEX will revolutionise our ability to systematically capture these early signatures, probing the full diversity of stripped progenitors and their explosive endpoints.

Short digest

Early multiwavelength follow-up of the Type IIb SN 2024uwq captures the shock-cooling bump and the subsequent second peak, with early spectra showing broad H-alpha (~15,500 km s^-1) and He I P-Cygni features of comparable strength that evolve toward stronger He and fading H. Modeling of the shock-cooling phase and a bolometric light-curve fit (two-component Arnett) favor a partially stripped progenitor with radius 10–60 R_sun and a residual hydrogen envelope of 0.7–1.35 M_sun. The inferred ZAMS mass of 12–20 M_sun and likely binary stripping place SN 2024uwq between compact and extended IIb events. The work underscores the value of very-early UV/optical coverage for mapping the continuum of stripped-envelope progenitors.

Key figures to inspect

• Figure 2: Inspect the early-time multi-band light curves to locate the shock-cooling peak relative to t0=MJD 60558.63 and gauge its color/UV strength; the grey vertical lines mark spectra epochs to connect photometric phases with spectral evolution.
• Figure 3: Compare the absolute B-band light curve and UB/BV/gr/ri color evolution against IIb benchmarks (1993J, 2008ax, 2011dh, 2011fu, 2013df, 2016gkg) to see why 2024uwq sits between compact and extended IIb (width and spacing of the two peaks, color tracks).
• Figure 4 (left): Use the bolometric luminosity with temperature and photospheric-radius evolution to identify the epochs used for shock-cooling modeling (T_BB > 8120 K) and to see the growth/decline of R_ph through the first and second peaks.
• Figure 4 (right): Examine the two-component Arnett MCMC fit to see how inner vs outer ejecta components reproduce the second peak and tail, informing Ni heating vs extended-envelope contributions.
• Figure 1: Check field/host context in NGC 6902 and precise SN location for follow-up aperture choices and potential host-background systematics.