SuperNova Remnants (SNR)

Transcription

1 SuperNova Remnants (SNR) Outline: SN classification (based on optical) Which ones are radio detected Models & caveats Physical properties

2 Supernova Remnants Further reading: Weiler et al. 00, ARAA, 40, Radio Emission from Supernovae and Gamma-Ray Bursters Smartt 009, ARAA, 47, Progenitors of Core-Collapse Supernovae Holoien + 017, The ASAS-SN Bright Supernova Catalog -- III. 016 Matsuura+, 017, ALMA spectral survey of Supernova 1987A molecular inventory, chemistry, dynamics and explosive nucleosynthesis Chap 15, Fanti & Fanti

3 SuperNova Remnants (SNR) Supernovae: Type I (in all galaxy types) Ia: old stars, WD exceeds the Chandrasekar's limit, No H lines, m ~ same profile of the light curve: maximum (M ~ 18.5 ) it lasts for ~ a week, max then decrease of 3m in ~75 days, then exponential decay strong SiII absorption, vexp ~ 104 km s 1 No radio emission (at 0.1 mjy level) Wrong! Ib, Ic: m younger stars, ~1.5 fainter, redder and often assiocated to HII regions no SiII lines, but He lines (Ib, if no He lines Ic), Massive stars that lost their envelope (stellar wind? Mass transfer to a companion?), possibly WR stars (strong) radio emission when young, fast decay of radio emission

4 SuperNova Remnants (SNR) Supernovae: Type II (in spirals only) Inhomogeneous class (all but type I!) Strong Hα emission, Mmax ~ m, with a lot of dispersion, from red giants, vexp ~ a few 103 km s 1, with some dispersion produce (weak) radio emission, relatively slow decay II-L: II-P:

5 SuperNova Remnants Comparison SN: type I.vs. type II Type I 1 Msun 10 4 km s erg Type II Ejected mass V exp Kinetic energy 1 Msun 10 4 km s erg Ia no radio emission (??), Ib/c steep radio spectrum α 1 II radio emission with a wide range of luminosities, fainter than I, flatter spectrum α 1 Only ~0% of supernovae have a radio counterpart ~1/4 of them are type Ib/Ic, ~3/4 are type II

6 SuperNova Remnants Radio emission is generally a non-thermal power law as from synchrotron emission i.e. B field & relativistic particles, the latter requiring some acceleration mechanism At the very beginning, radio emission is optically thick then becomes thin at progressively lower frequencies, and the light curve (decline) is similar to optical Radio emission may be produced by a. Rotating B field associated to a NS, accelerating electrons to relativistic regime b. The outer layers/shells expands supersonically in a circum-stellar medium filled by stellar wind of the pre-sn accelerating particles

7 Supernova Remnants Radio light curves: Peak at later times for lower frequencies Perez Torres +, 001 SN 1993J

8 Supernova Remnants Radio light curves: Marcaide + 00 SN 1979C in M100 High frequencies have faster evolution Measured deceleration!

9 Supernova Remnants A blast wave is expanding in an inhomogeneous CSM Variations in the CSM density & temperature are responsible for irregular evolution of the light curve The light curve may be used to to study the history of the stellar wind Weiler et al. 00

10 Supernova Remnants Timeline and dynamical evolution: Four main phases corresponding to different physics and light curve 1. Free expansion. Adiabatic expansion 3. Radiative/isothermal expansion 4. Fading and death N.B. There are transition phases in which there is not a dominant process

11 Supernova Remnants 1. Free (abiabatic) expansion The ejected mass largely exceeds that of the CSM swept by the shock (blast) wave (vexp» cs). v exp = constant T ejecta V Γ 1 = constant T ejecta α R 3(Γ 1) T shocked remains constantly high as long as v exp is constant The ejected material cools quite rapidly with time (i.e. R) The entrained material is heated at about the same temperature This fast stage lasts for yr The SNR has a size < 1 pc

12 Supernova Remnants. Adiabatic expansion (Sedov phase, energy conservation) M ejecta M entrained 3 If ncsm = 1 cm 4 3 π[r (t )]3 ρcsm M ejecta = 1 M where ρcsm =ncsm mh v exp = km s 1 Such phase start after about 00 yr after the SN explosion, when the remnant has a size of about pc. A thin spherical shell (most of the mass concentrated behind the shock) is expanding. The initial kinetic energy of the ejecta Uo is being transferred to the entrained mass as both kinetic ( Uk) and thermal ( Uth) energy, about evenly distributed. The total energy, as well as the kinetic and thermal energies, are preserved. In particular: Uk = Uo = M entrained v exp (t) ( 3 ) π[r (t )] ρcsm v exp (t )

13 Supernova Remnants: adiabatic expansion() Uk = 1 Uo = 1 exp M entrained v (t ) ( ) π[r (t )] ncsm mh [ ] d R (t ) dt If we integrate, assuming a negligible initial radius of the shell Ro, it is possible to obtain R (t ) = ( )( 75 8π 1 /5 Uo ncsm mh ) 1/ 5 v exp (t ) = R (t) 6 10 t 4 / ( ) Uo ncsm 1 /5 5 t 4 3 /5 ( ) Uo 1/ 5 ncsm = t /5 R (t ) 5 t vexp decreases with time (entrained material slows down the expansion) If ncsm, t, and vexp are known Uo can be derived t and vexp are easy to measure, then the ( Uo / ncsm ) ratio can be obtained

14 Supernova Remnants: adiabatic expansion(3) Hugoniot Rankine conditions provide: ρshocked = 4 ρcsm p shocked = 11 T = ρcsm v exp T shocked = ( ) () ( )() 4 3 /5 / 5 Uo 10 P = ncsm / 5 ncsm 51 Uo / 5 t yr t 6/ 5 o yr 6/ 5 3 mh v exp 16 k K dyne cm Typical temperatures ~ 5 x 10 8 ok, emission via bremsstrahlung (X-Rays) in a very thin outer shell. ( ) du o dt br V SNR J br (T ) [R (t )]3 ne T 1 / U 4o /5 t 3 /5 erg s 1

15 Image Credit: X-ray: NASA/CXC/SAO/J.Hughes et al, Optical: NASA/ESA/Hubble Heritage Team (STScI/AURA)

16 Supernova Remnants: adiabatic expansion(4) Time dependent bremsstrahlung losses are: ( ) du o dt br V SNR J br (T ) [R (t )]3 ne T 1 / U 4o /5 t 3 /5 erg s 1 at a given time the total energy radiated via bremsstrahlung is t W br o ( ) du dt 1 dt = / 5 8 /5 Uo t erg the fraction of the initial energy lost via bremsstrahlung radiation is W br 1 1/ 5 8/ 5 6/ U o t ncsm Uo In general, the radiated energy via bremsstrahlung is a small fraction (~1%) of the initial energy over several in 10 4 yr, and then the process can be considered adiabatic

17 Supernova Remnants: adiabatic expansion(5) The kinetic energy of the SNR is half of the initial energy: K= ( ) π ρcsm R v exp 1 = π ρcsm R R U o 3 3 dk if energy is conserved, then = 0 dt expansion is driven by thermal pressure and after some maths it comes out that the shell HOWEVER, beyond bremsstrahlung, also recombination lines of heavy elements (C, N, O) take place ( ) du dt CNO 17 = 8 10 ncsm T 3 4 9/ 5 1/ 5 1/5 R (t ) = 3 10 ncsm U o t in the adiabatic phase They grow much faster than bremsstrahlung losses and will become dominant ending the adiabatic phase

18 Supernova Remnants: adiabatic expansion(6) Integrating ( ) du dt 17 = 8 10 ncsm T CNO 3 4 9/ 5 1/ 5 1/5 R (t ) = 3 10 ncsm U o t And solving for t we get t 4 /17 9 /17 13 U o ncsm which correspond to a radius 5 5/ 17 7 /17 3 1/ 17 / 17 CSM R (t ) U o ncsm v exp (t ) 5 10 U and the expansion velocity is n In case Uo = 1050 erg, ncsm = 1 cm -3 we get t yr R (t ) 30 pc v exp (t ) 50 km s 1 The temperature of the expanding shell has decreased to a few in 104 ok and its pressure cannot support the expansion anymore End of adiabatic phase

19 Supernova Remnants: radiative phase 3. Radiative phase: i.e. end of the adiabatic phase: very efficient radiative losses energy cannot be considered constant any more. The SNR enters the isothermal phase: the energy transferred to CSM (implying an increase) is nearly immediately radiated (leaving T unchanged! Compression is not limited to 4 (H-R conditions) anymore and can reach 100s Now momentum conservation holds: 3 3 [R (t )] ncsm mh v exp = [R (t )] ncsm mh ( dr (t ) dt ) 3 = [R (t )] ncsm mh ( dr (t ) dt ) Integrating we get: 1/ 4 3/ 4 R (t ) ( t +const ) v exp (t ) ( t +const ) And the kinetic energy decreases as the the expansion progressively slows down K (t ) 1 m v exp v exp 1 Uo ( v exp (t ) v exp (t ) ) 3/ ( t +const ) = const

20 Supernova Remnants: radiative phase () At the end of the adiabatic phase the internal (thermal) pressure of the expanding gas becomes comparable or even smaller than the relativistic particles. In that case, the expansion of the shell is powered by relativistic particles whose pressure is represented as cosmic rays pressure (inclusive of protons!) d (mv ) dt ( U CR 1 = π ncsm mh [R (t )] R +4 π ncsm mh R R = 4 π [R (t )] 3 3 4/3 π R (t )3 4 Assuming that CR (relativistic particles) expands adiabatically, with no subsequent (interaction) re-acceleration or particle injection we can integrate and get [ R (t )] = 3 U CRo R o π ncsm mh R (t ) + const 6 R (t ) and, integrating again 1/ 3 R (t ) ( t +const ) 3 U CRo π ncsm mh R (t ) + const 6 R (t) v )

21 Supernova Remnants 4. Fading away: The radius of the remnant grows slower and slower R(t) α t s, where s < 1/4, the expansion speed is <~ 0 km/s and T ~10000 K, size > 30 pc The shell merge and fades into the ISM mixing with it (1 Myr after the explosion) and cannot be distinguished anymore.

22 Supernova Remnants 4. Fading away: The radius of the remnant grows slower and slower R(t) α t s, where s < 1/4, the expansion speed is <~ 0 km/s and T ~10000 K, size > 30 pc The shell merge and fades into the ISM mixing with it (1 Myr after the explosion) and cannot be distinguished anymore.

23 Supernova Remnants: Radio properties Radio images: morphologies Angular Size Distance Linear size Cas A 3'x3' 3.4 kpc... Tycho 6'x6'.3 kpc... W50 º x 1º 5.5 kpc... Tycho: VLA image at 1.4 GHz (Reynolds, R.A. Chevalier) Crab Nebula:VLA image at 5 GHz. Image courtesy of NRAO/AUI and M. Bietenholz Cas A: VLA image from 3 different frequencies: 1.4, 5.0 and 8.4 GHz. (NRAO image gallery, Rudnick +). W50: VLA image at 1.4 GHz (Dubner +)

24 Supernova Remnants: Radio properties Radio polarization: From Blast wave to Shock wave Old SNR, vectors are B field projection ( Han + 013, IAU Symp.) Cas A at 3 GHz (Dubner & Giacani 015)

25 Supernova Remnants: Radio properties Radio polarization () In young SNR the field is radial, likely stretched by the rapidly expanding material (blast wave) In old SNR H is tangential (as in MHD shock waves) In plerions the field is disordered B ~ G (both from equipartition and RM observations) depending on the size (age)

26 Supernova Remnants: Radio properties The Σ D relation: Σ = AD β pe Slo 4.5 In an adiabatically expanding radio source (filling factor Φ = 1, no reacceleration, frozen H field), the luminosity is L ~ D δ = D (α +1) and the surface brightness is Σ ~ L / D ~ D δ ~ D 4(α +1) In case the SNR is a thin shell L ~ D (3δ 1)/~ D 3α 1 Σ ~ D (3δ 1)/ ~ D 3(α +1) Σ D plot for M8 (crosses), GMC (encircled crosses) and O-rich SNRs (circles). Arbutina & Urosevic (005) In dense environments like those in figure, the slope is ~ -3.5 We might expect slight displacements depending on the SNR luminosity

27 Supernova Remnants: Radio properties The L D relation: L = AD η p Slo e.5 In an adiabatically expanding radio source L ~ D δ = D (α +1) In case the SNR is a thin shell L ~ D (3δ 1)/~ D 3α 1 Perhaps there is a correlation for SNR in dense environments There is no obvious correlation between luminosity and linear diameter, except for the M8 SNRs. Arbutina + (004)

28 Supernova Remnants: Radio properties Progenitor classification ~Certain only for recent events (optical spectroscopy, earlier observations of the progenitor) Old SNR cannot be classified for sure (light echoes, scattering of the explosion, e.g. Kraus + 008) IIb Arbutina & Urosevic (005) Kraus + (008)

29 Supernova Remnants SN1987A (3 Feb 1987, in the LMC) (see Giovanna Zanardo, PhD thesis) Type II, from a B3 (~ 0 Mo) star, optical peak MV ~ 14 Preceeded by ~ 0 neutrino events ( hr prior of the optical flash) 56 Optical light curve consistent with radioactive decays Ni β+ (6.1d) 56 Co γ+(77.1d) 56 Fe??

30 Supernova Remnants SN1987A...across the electromagnetic spectrum (in 1996 Chandra was launched yet) Radio light curve: flux densities for SN 1987A at 843 MHz between Feb 87 and May 000. Error bars are the quoted about 3% uncertainties. Ball et al. 001, ApJ, 549, 599 McCray

31 Supernova Remnants Radio emission: example SN1987A Prompt phase of radio emission which began almost immediately after the explosion, peaked about four days later, then decayed and became undetectable after just a few weeks. Second phase of radio emission from SN1987A, started in June 1990, some 3 and a half years after the explosion, and continues to brighten steadily. due to electrons accelerated at the supernova shock via the mechanism called `diffusive shock acceleration'. i.e. a shock which is very much weaker than expected from a supernova explosion. modification of the shock by other particles (mainly protons) which are also accelerated. The accelerated protons contribute significantly to the pressure in front of the shock Variations are related to inhomogeneities in the stratified CSM deposited by the stellar wind

32 Supernova Remnants SN1987A: The radio spectral index is flattening with time > 0.7

33 Supernova Remnants: Progenitors Schematic evol. tracks of the centers of single stars of various masses in the T-density plane (blue lines). Solid lines indicate hydrostatic evolution, big red dots indicate the start of the collapse of the core, and dashed lines imply hydrodynamic evolution, i.e., collapse or explosion. In the three light red areas, the stellar core is prone to collapse, whereas the brown area represents nonrelativistic electron degeneracy. Labels on the evolutionary tracks indicate the initial mass and the final fate. At high metallicity, mass loss may prevent the most massive stars from entering the region ofe ± production, whereas at very low metallicity, rotational mixing may lead stars above 60 M into the pair-unstable regime. Rapid rotation could also lead to the formation of long-duration gamma-ray bursts for those stars that produce black holes (BH) or neutron stars. Abbreviations: CCSN, iron core-collapse supernova; ECSN, electron-capture supernova; PISN, pair-instability supernova

34 Supernova Remnants H-R diagram of the STARS evolutionary tracks (Eldridge & Tout 004). The location of the classical luminous blue variables (LBV) is from Smith, Vink & de Koter (004). SN005gl had a luminosity of at least log L/L 6, which puts it in the LBV region indicated or at even higher luminosities if it was hotter and, hence, had a significant bolometric correction. The region where we should see Wolf-Rayet (WR) progenitors is shown, and the only progenitor detected close to this region is that of SN008ax. The red supergiants (RSG) where progenitors have been detected is shown again for reference.

35 Supernova Remnants A summary diagram of possible evolutionary scenarios and end states of massive stars. These channels combine both the observational and theoretical work discussed in this review, and the diagram is meant to illustrate the probable diversity in evolution and explosion. It is likely that metallicity, binarity, and rotation play important roles in determining the end states. The acronyms are neutron star (NS), black hole (BH), and pair-instability supernova (PISN). The probable rare channels of evolution are shown in red. The faint supernovae are proposed and have not yet been detected. (Smartt, 009)

36 Supernova Remnants Summary: SN are (relatively) rare events arising from two main progenitors: WD (SN Ia) and massive stars (Ib, Ic & type IIs) They deposit about 1051 erg into the CSM & ISM The radio emission is quite common (0 5%) and the radio luminosities spans a few (5) orders of magnitude, reaching a few in 10 0 W Hz 1 A radio emitting galactic SNR can be visible for a few in 10 7 yr, and reach a size of several 10s of pc SN provide CR supply, as well as metal enrichment of the ISM A model consisting of 4 main stages grossly describes the evolution of a (radio) SNR