Search

We present a JWST/MIRI low-resolution mid-infrared (MIR) spectroscopic observation of the normal Type Ia supernova (SN Ia) SN 2021aefx at +323 days past rest-frame B-band maximum light. The spectrum ranges from 4-14 um, and shows many unique qualities including a flat-topped [Ar III] 8.991 um profile, a strongly tilted [Co III] 11.888 um feature, and multiple stable Ni lines. These features provide critical information about the physics of the explosion. The observations are compared to synthetic spectra from detailed NLTE multi-dimensional models. The results of the best-fitting model are used to identify the components of the spectral blends and provide a quantitative comparison to the explosion physics. Emission line profiles and the presence of electron capture (EC) elements are used to constrain the mass of the exploding white dwarf (WD) and the chemical asymmetries in the ejecta. We show that the observations of SN 2021aefx are consistent with an off-center delayed-detonation explosion of a near-Chandrasekhar mass (Mch) WD at a viewing angle of -30 degrees relative to the point of the deflagration-to-detonation transition. From the strength of the stable Ni lines we determine that there is little to no mixing in the central regions of the ejecta. Based on both the presence of stable Ni and the Ar velocity distributions, we obtain a strict lower limit of 1.2 Msun of the initial WD, implying that most sub-Mch explosions models are not viable models for SN 2021aefx. The analysis here shows the crucial importance of MIR spectra for distinguishing between explosion scenarios for SNe Ia., Comment: 21 pages, 9 figures, 4 tables, accepted to ApJL; updated to accepted version

Developing an effective automatic classifier to separate genuine sources from artifacts is essential for transient follow-ups in wide-field optical surveys. The identification of transient detections from the subtraction artifacts after the image differencing process is a key step in such classifiers, known as real-bogus classification problem. We apply a self-supervised machine learning model, the deep-embedded self-organizing map (DESOM) to this ‘real-bogus’ classification problem. DESOM combines an autoencoder and a self-organizing map to perform clustering in order to distinguish between real and bogus detections, based on their dimensionality-reduced representations. We use 32 × 32 normalized detection thumbnails as the input of DESOM. We demonstrate different model training approaches, and find that our best DESOM classifier shows a missed detection rate of $6.6{{\ \rm per\,cent}}$ with a false-positive rate of $1.5{{\ \rm per\,cent}}$. DESOM offers a more nuanced way to fine-tune the decision boundary identifying likely real detections when used in combination with other types of classifiers, e.g. built on neural networks or decision trees. We also discuss other potential usages of DESOM and its limitations.

We report the identification of a source coincident with SN 2009kr in HST pre-explosion images. The object appears to be a single point source with an intrinsic colour V-I = 1.1 and M_V = -7.6. If this is a single star it would be a yellow supergiant of log L/L_{sol} \sim 5.1 and a mass of 15 (+5/-4) M_{sol}. The spatial resolution does not allow us yet to definitively determine if the progenitor object is a single star, a binary system, or a compact cluster. We show that the early lightcurve is flat, similar to IIP SNe, but that the the spectra are somewhat peculiar, displaying unusual P-Cygni profiles. The evolution of the expanding ejecta will play an important role in understanding the progenitor object., Comment: Submitted to ApJ Letters

The progenitors of many type II core-collapse supernovae have now been identified directly on pre-discovery imaging. Here we present an extensive search for the progenitors of type Ibc supernovae in all available pre-discovery imaging since 1998. There are 12 type Ibc supernovae with no detections of progenitors in either deep ground-based or Hubble Space Telescope archival imaging. The deepest absolute BVR magnitude limits are between -4 and -5. We compare these limits with the observed Wolf-Rayet population in the Large Magellanic Cloud and estimate a 16 per cent probability we have failed to detect such a progenitor by chance. Alternatively the progenitors evolve significantly before core-collapse or we have underestimated the extinction towards the progenitors. Reviewing the relative rates and ejecta mass estimates from lightcurve modelling of Ibc SNe, we find both incompatible with Wolf-Rayet stars with initial masses >25Msun being the only progenitors. We present binary evolution models that fit these observational constraints. Stars in binaries with initial masses, Accepted by MNRAS. 31 pages, 12 figures, 8 tables