Daryl Janzen

K. Bostroem, J. Pearson, M. Shrestha, D. Sand, S. Valenti, S. Jha, J. Andrews, N. Smith, G. Terreran, E. Green, Y. Dong 董, M. Lundquist, J. Haislip, E. Hoang, G. Hosseinzadeh, D. Janzen, J. Jencson, V. Kouprianov, E. Paraskeva, N. M. Meza Retamal, D. Reichart, I. Arcavi, A. Bonanos, M. Coughlin, Ross Dobson, J. Farah, L. Galbany, C. Gutiérrez, S. Hawley, L. Hebb, D. Hiramatsu, D. Howell, T. Iijima, I. Ilyin, K. Jhass, C. McCully, S. Moran, B. Morris, A. C. Mura, T. Müller-Bravo, J. Munday, M. Newsome, M. Pabst, P. Ochner, E. P. Gonzalez, A. Pastorello, C. Pellegrino, L. Piscarreta, A. Ravi, A. Reguitti, Laura Salo, J. Vinkó, K. de Vos, J. Wheeler, G. Williams, S. Wyatt

We present the optical spectroscopic evolution of SN 2023ixf seen in subnight cadence spectra from 1.18 to 15 days after explosion. We identify high-ionization emission features, signatures of interaction with material surrounding the progenitor star, that fade over the first 7 days, with rapid evolution between spectra observed within the same night. We compare the emission lines present and their relative strength to those of other supernovae with early interaction, finding a close match to SN 2020pni and SN 2017ahn in the first spectrum and SN 2014G at later epochs. To physically interpret our observations, we compare them to CMFGEN models with confined, dense circumstellar material around a red supergiant (RSG) progenitor from the literature. We find that very few models reproduce the blended N iii (λλ4634.0,4640.6)/C iii (λλ4647.5,4650.0) emission lines observed in the first few spectra and their rapid disappearance thereafter, making this a unique diagnostic. From the best models, we find a mass-loss rate of 10−3–10−2 M ⊙ yr−1, which far exceeds the mass-loss rate for any steady wind, especially for an RSG in the initial mass range of the detected progenitor. These mass-loss rates are, however, similar to rates inferred for other supernovae with early circumstellar interaction. Using the phase when the narrow emission features disappear, we calculate an outer dense radius of circumstellar material R CSM,out ≈ 5 × 1014 cm, and a mean circumstellar material density of ρ = 5.6 × 10−14 g cm−3. This is consistent with the lower limit on the outer radius of the circumstellar material we calculate from the peak Hα emission flux, R CSM,out ≳ 9 × 1013 cm.

G. Hosseinzadeh, J. Farah, M. Shrestha, D. Sand, Y. Dong 董, P. Brown, K. Bostroem, S. Valenti, S. Jha, J. Andrews, I. Arcavi, J. Haislip, D. Hiramatsu, E. Hoang, D. Howell, D. Janzen, J. Jencson, V. Kouprianov, M. Lundquist, C. McCully, N. M. Meza Retamal, M. Modjaz, M. Newsome, E. P. Gonzalez, J. Pearson, C. Pellegrino, A. Ravi, D. Reichart, N. Smith, G. Terreran, J. Vink'o

We present the densely sampled early light curve of the Type II supernova (SN) 2023ixf, first observed within hours of explosion in the nearby Pinwheel Galaxy (Messier 101; 6.7 Mpc). Comparing these data to recently updated models of shock-cooling emission, we find that the progenitor likely had a radius of 410 ± 10 R ⊙. Our estimate is model dependent but consistent with a red supergiant. These models provide a good fit to the data starting about 1 day after the explosion, despite the fact that the classification spectrum shows signatures of circumstellar material around SN 2023ixf during that time. Photometry during the first day after the explosion, provided almost entirely by amateur astronomers, does not agree with the shock-cooling models or a simple power-law rise fit to data after 1 day. We consider the possible causes of this discrepancy, including precursor activity from the progenitor star, circumstellar interaction, and emission from the shock before or after it breaks out of the stellar surface. The very low luminosity (−11 mag > M > −14 mag) and short duration of the initial excess lead us to prefer a scenario related to prolonged emission from the SN shock traveling through the progenitor system.

M. Shrestha, K. Bostroem, D. J. Sand, G. Hosseinzadeh, J. Andrews, Y. Dong 董, E. Hoang, D. Janzen, J. Pearson, J. Jencson, M. Lundquist, Darshana Mehta, A. Ravi, N. M. Meza Retamal, S. Valenti, P. Brown, S. Jha, Colin W. Macrie, B. Hsu, J. Farah, D. Howell, C. McCully, M. Newsome, E. Padilla Gonzalez, C. Pellegrino, G. Terreran, L. Kwok, N. Smith, M. Schwab, Aidan Martas, Ricardo R. Muñoz, G. Medina, Ting S. Li, Paula Diaz, D. Hiramatsu, Brad E. Tucker, J. Wheeler, Xiaofeng Wang, Q. Zhai, Jujia Zhang, A. Gangopadhyay, Yi Yang, C. Gutiérrez

We present high-cadence photometric and spectroscopic observations of supernova (SN) 2024ggi, a Type II SN with flash spectroscopy features, which exploded in the nearby galaxy NGC 3621 at ∼7 Mpc. The light-curve evolution over the first 30 hr can be fit by two power-law indices with a break after 22 hr, rising from M V ≈ −12.95 mag at +0.66 day to M V ≈ −17.91 mag after 7 days. In addition, the densely sampled color curve shows a strong blueward evolution over the first few days and then behaves as a normal SN II with a redward evolution as the ejecta cool. Such deviations could be due to interaction with circumstellar material (CSM). Early high- and low-resolution spectra clearly show high-ionization flash features from the first spectrum to +3.42 days after the explosion. From the high-resolution spectra, we calculate the CSM velocity to be 37 ± 4 km s−1. We also see the line strength evolve rapidly from 1.22 to 1.49 days in the earliest high-resolution spectra. Comparison of the low-resolution spectra with CMFGEN models suggests that the pre-explosion mass-loss rate of SN 2024ggi falls in the range of 10−3–10−2 M ☉ yr−1, which is similar to that derived for SN 2023ixf. However, the rapid temporal evolution of the narrow lines in the spectra of SN 2024ggi (R CSM ∼ 2.7 × 1014 cm) could indicate a smaller spatial extent of the CSM than in SN 2023ixf (R CSM ∼ 5.4 × 1014 cm), which in turn implies a lower total CSM mass for SN 2024ggi.

B. Subrayan, D. Sand, K. Bostroem, S. Jha, A. Ravi, M. Schwab, Jennifer E. Andrews, G. Hosseinzadeh, S. Valenti, Y. Dong 董, J. Pearson, M. Shrestha, L. Kwok, E. Hoang, J. Rho, S. Park, Sung-Chul Yoon, T. Geballe, J. Haislip, D. Janzen, V. Kouprianov, Darshana Mehta, N. M. Meza Retamal, Dan Reichart, M. Andrews, J. Farah, M. Newsome, D. Howell, C. McCully

We present early multiwavelength 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 Hα (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 Hα decreases, consistent with a hydrogen envelope (Menv = 0.7–1.35 M⊙) 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⊙, consistent with a blue/yellow supergiant with an initial zero-age main-sequence mass of 12–20 M⊙ 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 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 revolutionize our ability to systematically capture these early signatures, probing the full diversity of stripped progenitors and their explosive endpoints.

B. Subrayan, D. Sand, K. Bostroem, S. Jha, A. Ravi, M. Schwab, Jennifer E. Andrews, G. Hosseinzadeh, S. Valenti, Yize Dong, J. Pearson, M. Shrestha, L. Kwok, E. Hoang, Jeonghee Rho, S. Park, Sung-Chul Yoon, T. R. Geball, J. Haislip, D. Janzen, V. Kouprianov, Darshana Mehta, N. Retamal, D. Reichart, M. Andrews, J. Farah, M. Newsome, D. Howell, C. McCully

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.