5-9 nov 2012tsinghua transient workshop light curves and spectra
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5-9 Nov 2012 Tsinghua Transient Workshop
Light curves and Spectra
5-9 Nov 2012 Tsinghua Transient Workshop
SN Light Curves
• A SN shines for different reasons, and different types of SN may only show some of the various mechanisms
• Some SN classification is done on the basis of the Light curve properties
• The only phase common to all SNe is the radioactive phase, with
56Ni56Co56Fe
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SN Light Curves
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4 main phases1. Shock breakout
- star is hot, L~R*, rapid
2. Recombination phase (H-rich SNe)- envelope recombines, Light emitted: L,
t ~ M(env), R(env)
3. Radioactive heating (long diffusion times)- 56Ni, 56Co decay: ’s, deposition, optical photons
L ~ M(56Ni), M*, ; t ~ M*, , KE
• Radioactive tail (short diffusion times)- 56Co decay: prompt optical photons
L ~ M(56Ni); t ~ M*, , KE
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Different types of SNe have different light curves
SN Type
prog Shock Rec Rad. Heat.
Rad. Tail
II RSG (BSG)
IIP (87A)
(small R)
Ib/cCores (WR)
(small R)
(no H)
IaCores (WD)
(small R)
(no H)
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Type II SNe79C: IIL (small H env. - no Rec. Phase)
93J: Ib (very small H env.: He lines)
87A: IIP-pec (BSG prog - small R)
97D: IIP (faint) (large envelope, small KE - long plateau)
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SN 1987A : contributions to the LC
Shock breakout
Radioactive Heating
Radioactive Tail
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Shock breakout
• Explosion KE of SN ~ , >> binding En of star
Expansion velocity is supersonic: Shock Wave
• When this reaches the surface, the star gets hot and bright
• Thermal En.: • If (1 ‘foe’),
RSG progenitor T~106K
• But • Very bright!
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Shock breakout /2
• But this phase is very short-lived (~1day):
• Adiabatic cooling:
• Radiation dominates:
• Gas cools before it can contribute radiation to the LC
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Adiabatic Cooling• But some luminosity does escape
• If no other heating form,
• Where
• If E(rad) ~ 1/2 E(SN),
• Luminosity in this phase
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Recombination Phase
• H envelope recombines when T~ 6000 K(T~12000 K for He envelope)
• Most opacity in H-rich SNe is Thomson scattering on free electrons
• When H recombines, opacity drops• Recombined envelope ~ transparent to photons• Photosphere follows ionization front• Recombination wave moves inwards in vel space• During Recombination phase,
both Rph and L ~ constant: PLATEAU• This is only true if H-envelope is massive
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Plateau phase can last for months
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Radioactive heating
• Adiabatic and recombination Luminosity only high if R large, E/M large (M small), H-envelope present.
• Otherwise, need other source of energy
• In SNe, 56Ni is produced: this is radioactive
=8.8d =111d
56Ni 56Co 56Fe
e+ e+
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Radioactive decay/2
• Energy produced: – 56Ni: 3.9 1010 erg/s/g– 56Co: 6.8 109 erg/s/g
• ~96% of energy carried by ’s, rest by e+’s are efficiently trapped: k ~ 0.3 cm2/g
• Thermalisation to optical photons
• Optical photons must random-walk their way out in a large optical depth environment: kopt~0.1cm2/g
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Radioactive part of LC• When photons escape SN becomes bright• But the SN ejecta expand: density
decreases and so does opacity• Basic property: Maximum light occurs when
heating = cooling (Arnett’s Rule)• L(Max) M(56Ni)
• Radioactive heating dominates LC if R* small, no H-envelope: Type I SNe (also SN1987A after shock breakout)
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Radioactive Tail• At late times, opt<1, <1
• Only e+ deposit: ke+ ~ 7cm2/g, e+>>1
• LC follows 56Co decay rate (optical photons immediately emitted)
m = 0.98 mag/100d
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Radioactive Tail/2• If envelope not massive, eventually even e+ may not
fully deposit, and LC will decline faster
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Radioactive Tail/3• For massive envelope (eg SN1987A)
56Co decay effective for a long time (2-3 yr), then other radioactive species with long decay times (eg 44Ti, 57Co) take over
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SN Light CurvesPeak Lum: 56Ni
Plateau: H-envelope, R*
(SNe IIL: small H-envelope
SN 1987A: small R*)
Tail: 56Ni, M, E
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SN Spectra
• Formation, Observables
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Early-time spectrum
Homologous expansion
(v ≈ R) Ejecta are dense“Photospheric
Epoch”
τ=1continuum
absorption
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• Ejecta are dense
pseudo-photosphere
• Lines have P-Cygni profiles with
But velocities are high:
many lines overlap:
“Line Blanketing”
Early-time spectrum
phabs vv ~
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Montecarlo approach
• SN envelope expands like Hubble flow:
• Photons continously redshifted
• They can only interact with the next red line
• Easy to treat in MC
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Montecarlo spectra• Treatment of ionization/excitation includes
approximate NLTE (nebular approx.)
• Excited states
• Ground/metastable states: LTE
• Ionization: modified Saha
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Photon Travel in Montecarlo scheme
Abbott & Lucy 1985
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Treatment of Opacities in MC
Mazzali & Lucy 1993
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Photon Branching in MC
Mazzali 2000
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The effect of Photon Branching
Mazzali 2000
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Testing different distances
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Testing different risetimes
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Late-time spectra
Ejecta are thin:
“Nebular Epoch”
Gas heated by deposition of γ’s and
cooled by forbidden line emission
+e
Spectrum: no continuum.
Emission line profiles depend on velocity, abundance distribution.
Homologous expansion, homogenous density and abundance: parabolic profiles
τ < 1
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Late-time spectra
• Solve gamma-ray deposition, NLTE equations for state of gas
• Emission in mostly forbidden lines
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Supernova ClassificationMaximum light spectra
H / no H
SNe II SNe I | |
Light Curve shape Si / no Si
SNe IIL SNe IIP SNe Ia He / no He
SNe Ib SNe Ic
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Spectral Classification
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Supernova ClassificationLate-time spectra (6mo-1yr)
H / no H
SNe II SNe I | | O, H Fe, no O / O
SNe Ia SNe Ib/c
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Properties of SNe
early lat e radio gal axy light curve M(Ni) (M)
H He Si H O E S peak tail ~0.6
Ia nar fast ~0.1
Ib nar fast ~0.1
Ic nar fast ~0.1
II brd slow-IIP nar-IIL
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SNe II
H lines dominate at all times
H Ca II
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Properties of SNe from spectra: SNe II
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Properties of SNe from spectra: SNe II
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SNe II: spectral evolution reflects structure of massive star
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Early times: outer layers visible
Late times: inner part exposed
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SN1987A - confirmation of core collapse
Core-collapse of massive star• Catalogued star SK-69 202
• M=17M
• Teff=17000
• Log L/ L = 5.0
• Star has disappeared• Neutrinos confirm neutron star
formation• No pulsar or neutron star yet
seen
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Red supergiant progenitor - SN2003gd
SN1987A progenitor was a blue supergiant. Progenitor detection difficult. Only one example of a red supergiant of a normal Type II supernova
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SNe IIL: small H-envelope
These are rare events, showing a rapid (Linear) decline with no plateau: e.g. SN1980K
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SNe IIL: small H-envelope
Spectra show weak absorptions, often emission lines, indicative of interaction with surrounding CSM gas
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Early time: small H-envelope + CSM
CSMLate time: core
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SNe IIn: extreme case of interactionSimilar to IIL: early signs of interaction,
but interaction luminosity sustains LC for a long time: e.g. SN1995G
These can be among the brightest SNe
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SNe IIn spectraDominated by interaction: narrow H lines
indicate massive CSM
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SNe IIn spectraDominated by interaction: massive CSM
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SNe IIn: massive H-envelope
Star collapsed while H-envelope was being shedded, SN strongly interacts with surrounding CSM gas
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Early time: small H-envelope + CSM
CSM
Late time: core
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SNe IIn: ejecta-CSM interaction
Two shock are launched at the contact discontinuity
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SNe IIn: ejecta-CSM interactionWind may be clumpy
Narrow (few 100 km/s): clumpy wind
Intermediate (~1000 km/s) : shocked wind
Broad (few 100 km/s): : shocked ejecta
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SNe IIb: an intermediate class?Early times:
Both H and He present
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SNe IIb: an intermediate class?Late times: O dominates, some weak H also present, with flat-top profile: H in a shell
H-envelope partially stripped
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early
late
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A binary progenitor?
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Detect hot star (B1 Ia) spectrum in spectum of SN1993J
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SN1993J had lost most of its H-envelope to a companion
Now companion is more massive
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New evolutionary track of companion after mass accretion
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SNe Ib
Early: optical: He , Ca, Si, some O IR: characteristic He lines
He lines require non-thermal excitation by fast particles
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SNe Ib
Late: O, Ca, Mg
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Early times: see He H-envelope lost
Late times: see CO core, as in SNe II
Stripped star
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SNe Ic
Early: optical: Fe , Ca, Si, O IR: evidence of He lines unclear
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SNe Ib/c
Early: He (Ib), Ca, Si, some O Late: O dominates, Ca
He lines require non-thermal excitation by fast particles
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SNe Ic
Late: O, Ca, Mg
Early times: see CO core H- and H envelopes lost
Late times: see CO core, as in SNe II, Ib
Star more stripped
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A Wolf-Rayet progenitor ?- SN2002ap
Progenitor detection difficult. Probably a Wolf-Rayet star (stripped massive star)
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An evolutionary sequence among core-collapse SNe
early late
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Btw, SNe Ib v. Ic: Helium
Ib
Ic
Ic
2.058µm1.083µm
(Taubenberger et al. 2006)
Strongest HeI lines in IR. 1 can cause confusion, 2 line unique
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Most nearby long-soft GRBs come with type Ic SNe
stripped stars are more fun
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Significance of spectrum
Broad lines
Large Kinetic Energy
“Hypernovae”
(only SN1998bw was associated with a GRB)
Narrow lines
“normal” KE (1 foe)
Normal SN Ic
Mazzali et al. 2002
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SNe Ib/c cover a range of Lum
• SN1998bw was as bright as a SN Ia
• It produced much more 56Ni than `normal’ core-collapse SNe (~ 0.5 M)
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SNe span a range of KE
• GRB/SNe have very high expansion velocities (optical velocities up to 0.1c track relativistic properties)
• XRF/SNe have lower velocities
after Pian et al. 2006, Nature
5-9 Nov 2012 Tsinghua Transient WorkshopIwamoto et al. 1998
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LC
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LC ∝κ 1/ 2M 3 / 4
E1/ 4
SN 1998bw: modelling
ergKE 52105×=
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GRB/SNe are highly aspherical
• Evidence in nebular spectrum (Oxygen line broader than Fe lines, Mazzali et al. 2001) but also
in light curve
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56Fe
16O
Spherical
Aspherical
FeII] 5200A
[OI] 6300A
Observed
Aspherical explosion:
aspect-dep line shape
Orientation 15 deg
Maeda et al. 2002
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Was SN 2003jd = 98bw off-axis?• It was almost as
bright at peak as SN1998bw (Mv = -18.7)
• Early-time spectra had broad lines, but closer to SN2002ap
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Prediction from asphericity: off-axis GRB/SNe
• Double-peaked [O I] line indicates edge-on SN
• SN Ic 2003jd had broad lines was luminous, and showed a double-peaked [O I] line
• but the presence of an off-axis GRB seems ruled out by radio limits (Soderberg et al. 2006)
• So, something’s missing
Mazzali et al. (2005)
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Which stars become which SNe?
SN types of nonrotating massive single stars as a function of initial metallicity and initial mass. Green horizontal hatching indicates the domain where SNe IIp occur. At the high-mass end of the regime they may be weak and observationally faint because of fallback of 56Ni. These weak SNe IIp should preferentially occur at low metallicity. At the upper right-hand edge of the SN II regime, close to the green line of loss of the hydrogen envelope, SNe IIL/b that have a H-envelope of ~2 Mo; are made (purple cross-hatching). In the upper right-hand quarter of the figure, above both the lines of H-envelope loss and direct black hole formation, SNe Ib/c occur; in the lower part of their regime (middle of the right half of the figure) they may be weak and observationally faint because of fallback of 56Ni, similar to the weak SNe IIp. In the direct black hole regime no "normal" (non–jet-powered) SNe occur since no SN shock is launched. An exception are pulsational pair-instability SNe (lower right-hand corner; brown diagonal hatching) that launch their ejection before the core collapses. Below and to the right of this we find the (nonpulsational) pair-instability SNe (red cross-hatching), making no remnant, and finally another domain where black hole are formed promptly at the lowest metallicities and highest masses (white) where no SNe are made. Single WDs also do not make SNe (white strip at the very left).
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Spectra of SNe: SNe Ia
Early phase: absorption lines Late phase: nebular lines
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The case of SNe Ia ASTRO: Calibration of SN luminosity
– Brighter SNe have broader LCs (Phillips 93)
PHYS: What causes Lum-light curve relation?
Observed normalised
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The case of SNe Ia• Observations near maximum
– Composition of outer layers, energetics
• Importance of late, nebular phase– Properties of inner layers, dominated by 56Ni
Mazzali et al. 1998Early Late
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The case of SNe Ia• Abundance tomography
– Model time series of spectra– Montecarlo and NLTE techniques– Complete description of SN
(Mazzali et al. 2008)
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The case of SNe Ia
Mazzali et al. (2007)
56Ni
Si
stable Fe
• The key to understanding Zorro diagram SN Ia behaviour– Study many SNe– Mass (Ni + Si) ~ const
• Mass burned ~ const• KE ~ const• Lum M(56Ni)• LC width opacity• M(Fe group)
– Links to progenitor/ explosion