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Constraining the ellipticity of magnetars powering superluminous supernovae
Takashi Moriya (NAOJ)
Thomas Tauris (Bonn)
MNRAS, 460, L55 (2016)
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Superluminous supernovae (SLSNe)
• SNe brighter than ~ -21 mag (or ~ 1e44 erg/s) • total radiation energy exceeds 1e51 erg
• usual SNe emit ~ 1e49 erg • comparable to kinetic energy of usual SNe
Pastorello et al. (2010)
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Magnetar model for SLSNe
NS
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Magnetar model for SLSNe
magnetar
• magnetar
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Magnetar model for SLSNe
magnetar
• magnetar • neutron star with
• rapid rotation
• strong magnetic field
Erot =12INS�2 � 2� 1052
�P
1 ms
��2
erg
tm =6INSc3
B2dipoleR
6NS�2
� 5�
Bdipole
1014 G
��2 �P
1 ms
�2
days
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Magnetar model for SLSNe
magnetar
• magnetar • neutron star with
• rapid rotation
• strong magnetic field
Erot =12INS�2 � 2� 1052
�P
1 ms
��2
erg
tm =6INSc3
B2dipoleR
6NS�2
� 5�
Bdipole
1014 G
��2 �P
1 ms
�2
days
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Light curve models
• B = 1e14 G, P = 2.6 ms
Nicholl et al. (2013)
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NSs are GW sources
• magnetars need to convert rotational energy to thermal energy almost in situ for SLSNe
• if magnetars are highly distorted, GW emission will be dominant way to lose their rotational energy
magnetar
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NSs are GW sources
magnetar
• magnetars need to convert rotational energy to thermal energy almost in situ for SLSNe
• if magnetars are highly distorted, GW emission will be dominant way to lose their rotational energy
• GW emission will just leave the SN ejecta without heating the ejecta.
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NSs are GW sources
magnetar
• magnetars need to convert rotational energy to thermal energy almost in situ for SLSNe
• if magnetars are highly distorted, GW emission will be dominant way to lose their rotational energy
• GW emission will just leave the SN ejecta without heating the ejecta.
• magnetars in SLSNe should not be highly distorted!
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EM emission vs GW emission
• EM emission timescale (dipole)
• GW emission timescale
• for SLSNe
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Constraint on magnetar ellipticities for SLSNe
Moriya & Tauris (2016)
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Probable origin of ellipticities: toroidal fields
Cutler (2002)
Braithwaite (2009)
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Constraint on toroidal field strengths
Btoroidal < ~ 1e16 GMoriya & Tauris (2016)
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Toroidal fields are required for stable poloidal fields
• Bdipole ~ 1e14 G (from LC modeling) • Btoroidal < ~ 1e16 G (from ellipticities)
• Bdipole/Btoroidal > ~ 0.01 • still OK (dipole field can be stable) • all SLSNe must have stable dipole if
they are powered by magnetars • a test for the SLSN magnetar model
Braithwaite (2009)
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Summary
• SLSNe may be powered by magnetars • Bdipole ~ 1e14 G, P ~ 1 ms
• magnetars must lose their rotational energy as EM emission • magnetar ellipticities must be small enough to avoid GW emission
• magnetar ellipticities must be less than ~ 1e-3 • Btoroidal < ~ 1e16 G
• Bdipole/Btoroidal > ~ 0.01 • dipole field can be stable
• a test for SLSN magnetar model
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