Ultra-stripped Envelope Supernovae

A summary of current the observational status of Ultra-stripped Envelope Supernovae.

Transcript

1. Ultra-stripped Supernovae Kishalay De, Yuhan Yao 20201023@ZTF-TN
2. Outline • Ultra-stripped Supernovae: Formation Channel • Summary of Observation: iPTF14gqr, SN2019dge, SN2019ehk, iPTF16hgs • What we have learnt from Observations • Questions to be Addressed → Discussion
3. I. Ultra-stripped Supernovae: Formation Channel Most SNe Ibc have ejecta mass of 2—5 M⊙ The envelope is stripped in binary evolution If ejecta mass <~ 1 M⊙ Need extreme stripping Need small companion radius
4. II. Summary of Observation • iPTF14gqr (De2018b) • SN2019dge (Yao2020) • SN2019ehk (De2020) • iPTF16hgs (De2018a)
5. Probing SN progenitors with flash spectroscopy Infant SN explosion SN shock breaks out of optically thick material. Produces early shock cooling emission. Shock breakout ionizes optically thin region at ~ 1014 cm. Produces narrow emission lines of CSM material. See Gal-Yam+ 2014, Yaron+ 2017 7/17
6. iPTF14gqr MNi ~ 0.03 M⊙ Mej ~ 0.2 M⊙
7. Zero Age Main Sequence (MS) binary Roche Lobe overflow (RLO) MS star - He star binary First Type Ib/c SN MS star - neutron star (NS) binary High mass X-ray binary Common envelope spiral in He star - NS binary Double NS system ?? Observations of galactic double neutron star systems suggest they were created in a low ejecta mass, low energy explosion (Piran+ 2006; Dewi+ 2005)
8. Zero Age Main Sequence (MS) binary Roche Lobe overflow (RLO) MS star - He star binary First Type Ib/c SN MS star - neutron star (NS) binary High mass X-ray binary Common envelope spiral in He star - NS binary He star (stable/unstable) RLO. Most He is ejected from the system Stripped He star + NS Intense mass loss forms expanding envelope. iPTF 14gqr: Ultra-stripped SN inside He-rich envelope Double NS system
9. SN2019dge Renv ~ 170 R⊙ Menv ~ 0.1 M⊙ MNi ~ 0.017 M⊙ Mej ~ 0.33 M⊙
10. SN2019dge +0.4 d, Early-time He II emission: Wind velocity ~500 km/s, RCSM ~ 5e+13 cm Mass loss rate ~ 10-4 M⊙ yr -1 +14 d, Photospheric phase: Helium-rich, no hydrogen Mg II in UV (interaction) +85 d, Late time: Both narrow (~300 km/s) And intermediate-width (~2000 km/s) emission (similar to SN Ibn)
11. SN2019ehk One of the nearest ‘Ca-rich’ transients (M100) Suggested to be a CO+He hybrid WD merger (Jacobson-Galan+ 2020) or a highly stripped core-collapse supernova (Nakaoka+ 2020)
12. But hydrogen ...
13. A low mass CO core of a core-collapse supernova
14. SN2019dge iPTF14gqr SN2019ehk iPTF16hgs (?) M ej ~0.33 M ⊙ ~0.24 M ⊙ ~ 0.7 M ⊙ ~ 0.6 M ⊙ M Ni ~ 0.017 M ⊙ ~ 0.08 M ⊙ ~ 0.02—0.07 M ⊙ ~ 0.02 M ⊙ R env ~ 170 R ⊙ ~ 860 R ⊙ ~ 130—1500 R ⊙ ~ 350 R ⊙ M env ~ 0.1 M ⊙ ~ 0.03 M ⊙ ~ 0.05 M ⊙ ~ 0.1 M ⊙ R CSM ~ 700 R ⊙ ~ 8500 R ⊙ ~ 14000 R ⊙ — Type SN Ib (?) SN Ic (Ca) SN IIb (Ca) SN Ib (Ca) Summary of observations Rate: 2%--12% of CCSNe
15. III. What we have learnt from Observations • Low mass helium stars appear to always expand before the explosion • Evidence of extended CSM produced by pre-explosion mass loss • High [Ca II]/[O I] in the nebular phase -- consistent with low O nucleosynthesis for lower CO core masses • Striking similarities to thermonuclear Ca-rich transients, but these appear exclusively in star forming galaxies.
16. Radius of stripped helium star will expand after case BB mass transfer Laplace (2020)
17. Tauris (2015) Helium star + NS explosions
18. IV. Questions to be addressed • Is the envelope (cooling emission) bound to the progenitor? The inferred R env almost exceeds the maximum photospheric radius reached by low-mass helium stars, challenging the assertion of Case BB mass transfer. • The inferred mass loss rates are too high to be sustained over a long time -- do low mass helium stars undergo intense pre-explosion mass loss? • What range of binary companions (MS, WD, NS, BH?) can produce the extremely stripped stars we see in the data? Relative rates? • Prospects for progenitor searches -- Extreme helium stars radiative mostly in the ultraviolet! Problematic for Galactic extinction + low UV sensitivity • Calcium ‘richness’ -- is the [O I] lines a reliable tracer of the progenitor mass for low mass progenitors? What role does mixing play? • How to distinguish from fast thermonuclear explosions: Can white dwarfs contain large amounts of hydrogen (> 0.01 solar masses) at explosion?