Supernovae. M. Della Valle. INAF-Napoli ICRANet-Pescara

Transcription

1 Supernovae M. Della Valle INAF-Napoli ICRANet-Pescara Nice, September

2 Supernova types Explosion trigger mechanisms SN & GRB connection

3 What Supernovae? SUPERNOVA = super - nova very bright new star (Baade & Zwicky 1934)

4 Guest Stars Date (AD) Type m max Discovered by Remnant 185? I? -8 Chinese RCW86 393? -1 Chinese 837? -8? Chinese IC I -10 Chinese/Arabs SN II -6 China/Japan/Chaco Canyon Crab Nebula 1181 II? -1 China/Japan 3C I -4 Tycho Brahe Tycho 1604 I -3 Kepler*/Galilei Kepler ca II +5? Flamsteed Cas A 1885 I ~ +6 Hartwig M II +2.9 Ian Shelton SN1987A

5 BUM! SN1987a SUPERNOVA!!! 5

6 SN phenomenology

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9 Nova Phenomenon: phenomenology similar to SN:different energetic scale

10 From 1885 to 1920: ~ 30 Nova Stars in M31

11 -9 Nova Vel XX Tau 1927

12 With all reserve we advance the view that a super-nova represents the transition of an ordinary star into a neutron star consisting mainly of neutrons. Such a star may possess a very small radius and extremely high density (Baade & Zwicky 1934) Fritz Zwicky illustrating the concept of Supernova

13 Supernova Classification PASP 1941

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15 Barbon, Ciatti & Rosino 1974

16 PASP 1941

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18 Interpreting spectra: P-Cygni Profiles

19 Patat et al. 1995

20 PASP 1941

21 SN Progenitors? SNe are observed in ALL Hubble type Galaxies

22 in all Hubble types PASP 1941 only in spirals

23 H i) I II ii) Site of the explosions: SNe-I = E/S0/Spirals + no-h in the spectra à relatively young and old stellar population à Pop II stars à Thermonuclear SNe (< 8 M ) SN-II = only in Spirals + H in the spectra à massive stars à young stellar population à Pop I starsà Core Collapse SNe (> 8 M )

24 H H Fe Fe

25 SN 2008bk Mattila et al See also Smartt 2009 à 8-16 M 25

26 How does a Star explode?

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30 The Golden Age 1980 about bg

31 A new SN class: Ib The criteria to classify the members of this subclass of type-i SNe just as peculiar objects were adopted in the literature for about 20 years. Only in the mid-1980s (Panagia 1985, Elias et al. 1985; Uomoto & Kirshner 1985; Wheeler & Levreault 1995) it was realized that sufficient observational differences did exist to justify having two separate classes of objects. Type-Ib SNe are characterized by spectra with no presence of H or very weak lines (Branch et al. 2002) and strong He I lines at 4471, 5876, 6678 and 7065 Å

32 Ib

33 Ib without (or very little He) = Ic (Wheeler & Harkness 1986)

34 SNe-Ib/c à CC-SNe Lack of H in the spectra Type-Ib/c SNe are observed only in late type galaxies Radio observations reveal the existence of a strong radio emission due to the interaction of the ejecta with a dense pre-explosion stellar wind (10 5/ 6 M yr 1 ) produced by the progenitor (Weiler et al. 2002)

35 and their Radio Light Curves SN1994I (Ic) SN1993J (IIb)

36 SNe-Ib/c à CC-SNe Type-Ib/c SNe are observed only in late type galaxies Lack of H in the spectra Radio observations reveal the existence of a strong radio emission due to the interaction of the ejecta with a dense pre-explosion stellar wind (10 5/ 6 M yr 1 ) produced by the progenitor (Weiler et al. 2002) Their progenitors are massive stars, possibly in binary systems (e.g. Panagia 1988, Maund et al. 2004), which undergo the collapse of their cores after they have lost the respective H or He envelopes, via strong stellar wind or transfer to a binary companion via Roche overflow

37 Ib He C/O Fe

38 Ib without (or very little He) = Ic (Wheeler & Harkness 1986) C/O O/Ne/Mg Fe

39 SNe-Ib, Ic and IIb belong to the Core-Collapse Family long-duration GRBs à SNe-Ibc

40 1987K IIb He Fe H Filippenko et al. 1989

41 SNe-IIb SNe-IIb are transgender objects that evolve from type- II (H lines in the spectra at maximum) into type Ib (lack of H lines during the nebular stage) Progenitors are massive stars that still retain a thin H envelope prior to exploding. Prototypical objects of this SN class are SN 1987K (Filippenko 1988) and SN 1993J (Swartz et al. 1993; Filippenko, Matheson & Hot 1993) Link between H-rich (type II) and H-deficient (Ib/c) SNe has been established [ M ] (Elmhamdi et al. 2006)

42 IIn Η Fe + Dense CSM 1998 S

43 SNe-IIn Their spectra are dominated by a broad Hα line (FWHM km/s) sometimes superimposed by a narrow emission component (FWHM 200/300 km/s). In this case the SN is dubbed as II-n, narrow (Schlegel 1990). SNe belonging to this class show strong H lines in emission without absorptions. Chugai (1997) pointed out that these SNe undergo a strong interaction with a dense wind generated by the progenitor during repeated episodes of mass loss prior to exploding (e.g. SN 1994aj Benetti et al. 1998).

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46 Conclusions Recent observations reveal the existence of a continuum of properties among the different CC-SN classes: SNe II à SNe IIb à SNe Ib à SNe Icà GRB-SNe MS > 8-10M ~30M ~40M M H > 1-15M ~ 10-1 /10-3 M <<10-5/-6 M P% ~1% ~2% 4% rate

47 What would cause a massive star to explode? Stars are gravitationally confined thermonuclear reactors. Each time one runs out of one fuel, contraction and heating ensue, unless degeneracy is encountered. The burning is transferred to a shell about the core while further contraction of the core will lead to a higher temperature and the next stage of fusion. For star > 8 M the core temperature will rise to a value high enough (T~ 10 9 /10 10 ) to burn O and Ne to form Si, S and Mg, via: 16 O+ 16 Oà 28 Si + a ; 16 O+ 16 Oà 32 S; 20 Ne+aà 24 Mg. A particular important reaction is 28 Si+ 28 Sià 56 Ni Since Ni decays to Co via 56 Nià 56 Co + e + + n and Co to Fe via 56 Coà 56 Fe + e + + n The decay chain ends here because Fe is stable. When the core has exhausted its supply of Si the Si+Si channel shuts off and the core of the star contracts until we get burning in a shell around the Fe core. This short summary explains the well known onion structure.

48 Massive stars undergo multi-layered shell burning Hydrogen. 10 Myrs, T=15 M K, ρ=5g/cm3 Neon..½ yr, 800MK, ρ= Helium. 500 Kyrs, T=100M K, ρ=700g/cm3 Oxygen.6days, T=1G K, ρ=10 7 Carbon. 600 yrs, T=600M K, ρ=10 5 g/cm3 Silicon..1day, T=3G K, ρ= Iron collapse < 0.1 second

49 The relative sizes of the burning layers in the onion structure of a red Supergiant SN progenitor H ~ 1 à cm He/C ~ 10-3 à cm O/Ne/Mg ~ 10-4 à 10 9 cm Si/S/Ca ~ 10-5 à 10 8 cm Fe < 10-6 à 10 7 cm

50 What would cause a massive star to explode? (cont d) The Fe core (about 1M ) cannot support itself and starts to contract and its T rises. What happens as the T further increases in the Fe core? Fe is at the top of the average binding energy curve, so that Fe can only decompose into elements of lower binding energy, which means a net absorption of energy and the ultimate collapse of the core: at about 6x10 9 K the photodisintegration of the Fe gives γ + 56 Fe à 13 4 He + 4n (it requires about 124 MeV or 1.5x10-5 erg/nucleon). With 2x10 57 protons in M CH, this corresponds to a total energy loss of 3x10 52 ergà the core contracts more rapidly

51 Core-Collapse Iron core no outward pressure. Gravity wins Star collapses rapidly Electron degeneracy can t stop it! Electrons and protons crushed together to produce neutrons Neutrons pushed together by force of gravity The core becomes a giant nucleus of neutrons: a neutron star

52 The Energy Budget of a CC-SN >1.4 M Fe Core collapses to Neutron Star R NS ~ 10 Km Gravitational binding energy: ΔΕ Β G M WD2 / R NS GM WD 2 /R Fe-core 3 x ergs Kinetic energy of explosion 1% x ΔE B Electromagnetic radiation 0.01% x ΔE B Gravitational waves 10-6 x ΔE B Neutrinos 99% x ΔE B

53 Light Curves

54 The lightcurve Without a late time energy source the SN would not be bright. 56 Ni 56 Co 56 Fe These radioactive decays produce γ and e + whose energies power the lightcurve at later stages. The lightcurve powered by the RD, peaks at 10-20d after the explosion and declines because of the increasing transparency of the ejecta to γ and due to the decreasing number of radioactive elements.

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58 Conclusions Recent observations reveal the existence of a continuum of properties among the different CC-SN classes: SNe II à SNe IIb à SNe Ib à SNe Icà GRB-SNe MS > 8-10M ~30M ~40M M H > 1-15M ~ 10-1 /10-3 M <<10-5/-6 M P% ~1% ~2% 4% rate

59 Pair-Instability SNe (Stars above 140M ) The core temperature of such a massive stars is so high (> 1Gk) that photons convert spontaneously to electron-positron pairs, then decreasing the photon pressure that supports the outer layers of the star and triggering the collapse. 59

60 Gala-Yam