「 Subaru UM 」＠ NAOJ, 30 Jan 2008 Supernovae are NOT spherical: The result from late-time spectroscopy by FOCAS “Asphericity in Supernova Explosions from.

「 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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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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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)


• The explosion mechanism(s) of Core-Collapse Supernovae (CC-SNe)?

• The explosion geometry of CC-SNe?

Questions

“Easier” questions

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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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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


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/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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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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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.


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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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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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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Interpretation: Geometry of CC-SNe

Average geometry of CC-SNe, Moderately aspherical.

First observational support of recently proposed explosion scenarios.

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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

「 Subaru UM 」 ＠ NAOJ, 30 Jan 2008 Supernovae are NOT spherical: The result from late-time spectroscopy by FOCAS “Asphericity in Supernova Explosions from.

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「 Subaru UM 」＠ NAOJ, 30 Jan 2008 Supernovae are NOT spherical: The result from late-time spectroscopy by FOCAS “Asphericity in Supernova Explosions from.