Nebular Hα emission in Type Ia supernova 2016jae

Abstract

There is a wide consensus that Type Ia supernovae (SNe Ia) originate from the thermonuclear explosion of CO white dwarfs (WDs), with the lack of hydrogen in the observed spectra as a distinctive feature. Here, we present supernova (SN) 2016jae, which was classified as an SN Ia from a spectrum obtained soon after its discovery. The SN reached a B-band peak of −17.93 ± 0.34 mag, followed by a fast luminosity decline with sBV0.56 ± 0.06 and inferred Δm15(B) of 1.88 ± 0.10 mag. Overall, the SN appears to be a ‘transitional’ event between a ‘normal’ SN Ia and a very dim SN Ia, such as 91bg-like SNe. Its peculiarity is that two late-time spectra, taken at +84 and +142 days after the peak, show a narrow line of Hα (with full width at half maximum of ∼650 and 1000 km s−1, respectively). This is the third low-luminosity and fast-declining SN Ia, after SN2018cqj/ATLAS18qtd and SN2018fhw/ASASSN-18tb, found in the 100IAS survey to show a resolved narrow Hα line in emission in its nebular-phase spectra. We argue that the nebular Hα emission originates in an expanding hydrogen-rich shell (with velocity ≤1000 km s−1). The hydrogen shell velocity is too high to be produced during a common envelope phase, though it may be consistent with some material stripped from an H-rich companion star in a single-degenerate progenitor system. However, the derived mass of this stripped hydrogen is ∼0.002–0.003 M⊙, which is much less than that expected (> 0.1 M⊙) from standard models for these scenarios. Another plausible sequence of events is a weak SN ejecta interaction with an H shell ejected by optically thick winds or a nova-like eruption on the CO WD progenitor some years before the SN explosion.

Constraining the Progenitor System of the Type Ia Supernova 2021aefx

“…These limits are also listed in Table 3. This Hα luminosity limit is comparable to, or fainter than, the recent detections identified in three fast-declining SNe Ia (Kollmeier et al 2019;Prieto et al 2020;Elias-Rosa et al 2021).…”

“…This appears to disfavor the singledegenerate scenario for most normal SNe Ia. However, three recent detections of Hα in fast-declining SNe Ia suggest that this channel may be physically allowed for some subluminous SNe Ia (Kollmeier et al 2019;Vallely et al 2019;Prieto et al 2020;Elias-Rosa et al 2021).…”

Early Lightcurves of Type Ia Supernovae are Consistent with Nondegenerate Progenitor Companions

“…This signature has not been observed for >100 SNe Ia with nebular spectra, often to very constraining limits of M stripped H < 10 −3 M (for recent compilations see Maguire et al 2016;Sand et al 2019;Tucker et al 2020). It has been observed in a handful of cases, namely SN 2016jae (Elias-Rosa et al 2021), SN 2018cqj (Prieto et al 2020), and SN 2018fhw (Kollmeier et al 2019). Curiously, all three SNe are underluminous, with M B,peak fainter than −18, and no Hα has been observed for any objects with an early UV excess including for SN 2017cbv (Sand et al 2018), SN 2018oh (Dimitriadis et al 2019bTucker et al 2019), or SN 2021aefx (Ashall et al 2022;Hosseinzadeh et al 2022).…”

Strong Carbon Features and a Red Early Color in the Underluminous Type Ia SN 2022xkq

“…As shown in Table 1, the resulting flux and luminosity limits (assuming D = 31 Mpc) are (1) Hα of 7.6 × 10 −17 erg s −1 cm −2 and 8.8 × 10 36 erg s −1 , (2) He I λ5875 of 3.4 × 10 −16 erg s −1 cm −2 and 4.0 × 10 37 erg s −1 , and (3) He I λ6678 of 7.6 × 10 −17 erg s −1 cm −2 and 8.8 × 10 36 erg s −1 . For reference, the Hα luminosity limit for SN 2022xkq is between ∼4 and 10 times fainter than the Hα detections seen in three recent low-luminosity, fast-declining SNe Ia with similar photometric properties to SN 2022xkq (Kollmeier et al 2019;Vallely et al 2019;Prieto et al 2020;Elias-Rosa et al 2021), indicating that we would detect such features if they were present.…”