「 subaru um 」 @ naoj, 30 jan 2008 supernovae are not spherical: the result from late-time...
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「 Subaru UM 」 @ NAOJ, 30 Jan 2008
Supernovae are NOT spherical: The result from late-time spectroscopy b
y FOCAS
“Asphericity in Supernova Explosions from Late-Time Spectroscopy”, Keiichi Maeda et al., Science, 31 January issue (online version)
Keiichi Maeda (@MPA → IPMU)MPA: Max-Planck-Institute for Astrophysics
IPMU: Institute for the Physics and Mathematics of the Universe
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「 Subaru UM 」 @ NAOJ, 30 Jan 2008
Collaborators
• K. Maeda (MPA/IPMU)• K. Kawabata (Hiroshima)• P.A. Mazzali (MPA/Trieste)• M. Tanaka (Tokyo)• S. Valenti (ESO)• K. Nomoto (Tokyo/IPMU)• T. Hattori (Subaru)• J. Deng (NAOC)• E. Pian (Trieste)
• S. Taubenberger (MPA)• M. Iye (NAOJ)• T. Matheson (Tucson)• A.V. Filippenko (UC Berkeley)• K. Aoki (Subaru)• G. Kosugi (NAOJ)• Y. Ohyama (JAXA)• T. Sasaki (Subaru)• T. Takata (NAOJ)
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「 Subaru UM 」 @ NAOJ, 30 Jan 2008
Core-Collapse Supernovae (CC-SNe)
(23rd Feb. 1987)
• The end product of a massive star ( M > 8 M
• Core-collapse Explosion ( E ~ 1051 erg )• Origin of heavy elements. • My talk is especially on “stripped” CC-SNe.
– A subclass, a progenitor has lost its H envelope before the explosion. SN 1987A (not stripped)
「 Subaru UM 」 @ NAOJ, 30 Jan 2008
• The explosion mechanism(s) of Core-Collapse Supernovae (CC-SNe)?
• The explosion geometry of CC-SNe?
Questions
“Easier” questions
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「 Subaru UM 」 @ NAOJ, 30 Jan 2008
Why geometry?
• Theoretical scenarios– SASI, rotation, MHD, Collapser…(and so forth)
(Some) Proposed scenarios predict bipolar explosions.
The geometry is closely related to the explosion mechanism.
Blondin+ 2003 Kotake+ 2004 MacFadyen & Woosley 1999
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「 Subaru UM 」 @ NAOJ, 30 Jan 2008
OK. Geometry seems important. But HOW CAN YOU LOOK INTO THAT?
• An SN is observed as a point source. – Only very few exceptions (e.g., 87A)
• Late-time spectroscopy (~ 1 year after the explosion)! – Optically thin (expansion) + simple velocity law (v r). ∝
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blueshift
redshiftwavelength
「 Subaru UM 」 @ NAOJ, 30 Jan 2008
Spherical models
• ANY spherical distribution should produce “SINGLE-PEAKED” [OI] 6300&6363. – 6363A component negligible at late-phase. – Negligible transfer effect to distort the line profile.
– Irrespective the radial density distribution, you always have the maximum cross section at the supernova center.
• The line should peak at the rest wavelength.
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「 Subaru UM 」 @ NAOJ, 30 Jan 2008
Subaru/FOCAS Observation
• Spectroscopy@200day.– Faint (R ~ 20 – 24 mag).– Often fainter than a backgroun
d diffuse HII region.
• ~ 0.5 – 4 hr by 8m!• Subaru/FOCAS (+ VLT)!
– KM, KK, MT + TH, KA.
• After subtracting possible biases (later), 15 SNe.
• Previously, only 3 SNe. • 18 SNe = 6 times the previo
us sample!!!
Previous
This work
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「 Subaru UM 」 @ NAOJ, 30 Jan 2008
Observational Result
• Discovery of the double-peaked [OI] in at least 5 SNe (at most 9) out of 18.
• The double-peak is NOT an unusual features!
• Asphericity is a common feature in SNe!!
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「 Subaru UM 」 @ NAOJ, 30 Jan 2008
To be more quantitative: Aspherical models
BP16 8 4 2 1
ρ
56Ni(Fe)
Ca
O
Spherical
Fe (56Ni)
O
At observations (>1day )
A sequence of phenomenological (parameterized) models. Params.: BP (Asphericity), θ
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Maeda+ 02, ApJ, 565, 405
Oxygen distributed in a disk.
「 Subaru UM 」 @ NAOJ, 30 Jan 2008
Statistics of the [OI] profile!
O
< 30oZ : 0 deg
R : 90 deg
0 deg
30 deg
60 deg
90 deg
Expected frequency 36%
Singly Peaked Maeda+ 06, ApJ, 640, 854
Extreme Model BP8
Expected frequency 64%
Doubly Peaked
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「 Subaru UM 」 @ NAOJ, 30 Jan 2008
Statistics of the [OI] profile
• BP8 = 64% double-peaked, BP2 = 34%, BP1 = 0%.
BP8 vs BP2
double vs. single
BP16 8 4 2 1
ρ
56Ni(Fe)
Ca
O
Spherical
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「 Subaru UM 」 @ NAOJ, 30 Jan 2008
Asphericity is a common feature, but HOW?
• Double peaked fraction = 28 – 50% (median 39%).– Uncertainty comes from “transitional” profiles.
vs.• BP8 predicts 64%, BP2 = 34%, and BP1 = 0%.
• Most, if not all, CC-SNe are NOT spherical. • On average, CC-SNe are moderately aspherical.
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「 Subaru UM 」 @ NAOJ, 30 Jan 2008
Interpretation: Geometry of CC-SNe
Average geometry of CC-SNe, Moderately aspherical.
First observational support of recently proposed explosion scenarios.
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「 Subaru UM 」 @ NAOJ, 30 Jan 2008
Conclusions & Implication
• Core-collapse SNe do have asphericity. – Mildly(?) aspherical (consistent with model BP2).
• Not discussed in this talk, but important implication.– The average asphericity looks smaller than specia
l, energetic SNe (Hypernovae). • Previous study indicates a geometry similar to BP8 for a very eberg
etic SN 1998bw (associated with a Gamma-ray burst).
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Maeda+ 06, ApJ, 640, 854; Maeda 06, ApJ, 644, 385; Maeda+ 06, ApJ, 645, 1331; Tanaka+ 07, 668, L19