1. Keck Observations of Two Supernovae Hours After Explosion Shock-Breakout Flash Spectroscopy as a New Window into the Evolution and Death of Massive Stars
Daniel Perley
(Caltech)
O. Yaron (Weizmann) A. Gal-Yam (Weizmann) E. Ofek (Weizmann) iPTF team

2. Palomar Transient Factory

3. Palomar Transient Factory

4. PTF → iPTF
PTF ( ): Various strategies, but typically 3-day cadence. Find large numbers of transients.
Intermediate PTF (2013-present): Various strategies, but typically 1-hour cadence.
(3 visits per night, every night) Find new types of fast-varying transients, and
find “ordinary” supernovae very early.

5. iPTF Nightly Scanning
Scanners
Palomar
Keck

6. iPTF 13ast UGC 7610 (D = 108 Mpc) 2013 May 3 04:14 UT
SDSS reference image
(Gal-Yam+2014,
Nature 509:471)

7. Keck Observations DEIMOS spectrum @ 0.64 days Fλ
LRIS 6.45 days
Wavelength (A)
DEIMOS trigger and spectum

8. Keck Observations DEIMOS spectrum @ 0.64 days FλHβ
DEIMOS 0.64 days
N III Fλ
HeII
C IV, He I Hα
N IV
LRIS 6.45 days
Wavelength (A)
DEIMOS trigger and spectum

9. Keck Observations DEIMOS spectrum @ 0.64 daysHβ
DEIMOS 0.64 days
N III
HeII
C IV, He I Hα
N IV
LRIS 6.45 days
DEIMOS trigger and spectum

10. Shock Breakout Below a Stellar Wind
star
X UV opt
(spectrum just above stellar surface)

11. Shock Breakout Below a Stellar Wind
star
shock
X UV opt
(spectrum just above stellar surface)

12. Shock Breakout Below a Stellar Wind
X UV opt
(spectrum just above stellar surface)

13. Shock Breakout Below a Stellar Wind
X UV opt
(spectrum just above stellar surface)

14. Shock Breakout Below a Stellar Wind
ionized wind
X UV opt
X UV opt
(spectrum just above stellar surface)

15. Shock Breakout Below a Stellar Wind
ionized wind
X UV opt
(spectrum just above stellar surface)

16. Shock Breakout Below a Stellar Wind
X UV opt
(spectrum just above stellar surface)

17. Shock Breakout Below a Stellar Wind
X UV opt
(spectrum just above stellar surface)

18. Flash Spectroscopy: Progenitor Diagnostic
Flash-excited spectrum resembles a Wolf-Rayet star of type WN(h)
(No oxygen: CNO-processed material is exposed in wind)
IIb progenitor is a WR? Perhaps not (Groh 2014), but evolutionary link probably exists

19. Pre-Explosion Behavior
Hα luminosity constrains mass-loss rate (for inner wind; probes material emitted in last ~10 years pre-explosion) ~ M☉/yr
Extremely rapid mass loss!
Cannot be steady-state and very unlikely to be coincidental: star was highly unstable just before explosion (onset of C burning...?)

20. iPTF 13dqy 2013 October 8 NGC 7610 (D = 51 Mpc)
SDSS reference image
(Yaron, Perley et al in prep.)

21. Early Keck Observations
0.26 d
r-band light curve
Swift UVW2 light curve
Wavelength (A)
LRIS trigger and spectra
time (days)

22. Early Keck Observations
0.26 d
O IV
O VI Hδ
He II Hγ Hβ Hα
O V
r-band light curve
Swift UVW2 light curve
Wavelength (A)
LRIS trigger and spectra
time (days)

23. 13dqy Spectra
0.26 d 0.30 d
0.37 d
0.42 d
0.88 d
1.4d
2.0d
5.3d 8.8d
10.9d
20.2d
22.4d
27.1d
31.3d
43.3d

24. 13dqy Spectra 0.26 d 0.30 d Flash-excited narrow lines 0.37 d 0.42 d
Hot continuum
II-P supernova

25. Line Profiles O IV, O V: No narrow core,
Continuum-subtracted spectrum
O IV, O V: No narrow core,
Broad component only (all material is inner; t >> 1) but, O VI has a weak narrow component?
H I, He II: Narrow core (recombination of outer material) + Broad wings (Thomson scattering of inner material)

26. Line Flux Evolution Hydrogen peaks at ~1.5 d; disappears between 6-8 d
He II peaks at ~1.0 d, disappears between 2-5 d
O V, O VI peak at <0.3 d and disappear by 2 d

27. Flash-Ionization and Light Travel Time
106
breakout
Unflashed wind
EUV-flashed wind
EUV flash: ~ hour
105
EUV flash
NUV flash
cooling
to Keck
NUV flash: ~day
104
NUV-flashed wind
pre-explosion
time
8 light-days (=1360 AU, =2.1 × cm)
surface temperature (K)

28. 13dqy Preliminary Results
Shock-breakout flash:
Flash temperature ~105 K, lasting ~1 hour
Mass-loss history:
Emitting region ~ few light days Recent mass-loss rate ~10- 4 M☉/yr (Again not steady-state – late instability?)
Slow wind velocity (< 100 km/s)
Red supergiant progenitor, exploding during a period of greatly enhanced mass loss.
Wind/surface composition:
H/O-rich. (Possibly N-poor?)

29. Stellar Wind Flash Tomography

30. The Future This is only the beginning!
Every core-collapse SN may very well behave this way.
2 out of 2 with <1 day observations Search of PTF archive finds several more transient H/He signatures in early (~few days) spectra.
Early SN Ia spectra taken so far do not show these features.
~1 SN at <100 Mpc per day
A few <1 day detections per year with iPTF
A few <1 day detections per month with ZTF
HIRES monitoring of a SN over first few days would provide detailed tomography of the spatially resolved wind Approved HST UV spectroscopy proposal starting next year (PI Gal-Yam)

31. Summary iPTF 13ast (II-b): H, He, N lines disappearing in <5 days
Progenitor was oxygen-depleted Enhanced mass loss / ejection in final years
iPTF 13dqy (II-P):
H, He, O lines disappearing in 1-5 days
Progenitor wind oxygen-rich RSG progenitor, with enhanced mass loss
All cc-SNe may show flash-excited early spectra, and All cc-SNe may undergo enhanced mass loss shortly before exploding.

33. Three Supernova SpectraFλ

34. Three Supernova Spectra
N IV
He II Hβ
C IV
N IV
He I Fλ
very hot SN IIn
Wavelength (A) Fλ
featureless hot continuum
featureless hot continuum
Fe II H
Ca II Fλ
SN IIb
He I
He I

35. Three Supernova Spectra
N IV
He II Hβ
C IV
N IV
He I
very hot SN IIn Fλ
featureless hot continuum
featureless hot continuum
Fe II
Wavelength (A) H
Ca II Fλ
SN IIb
He I
He I

36. Three Supernova Spectra
N IV
He II Hβ
C IV
N IV
He I
very hot SN IIn Fλ
featureless hot continuum
featureless hot continuum
Fe II H
Ca II
SN IIb
He I
He I

37. Three Supernova Spectra
t = 0.64 days
N IV
He II Hβ
C IV
N IV
He I
very hot SN IIn
t = 3.1 days Fλ
featureless hot continuum
featureless hot continuum
t = 69 days
Fe II H
Ca II
SN IIb
He I
He I