PoS(BASH 2013)009 http://pos.sissa.it/ † ∗ [email protected] Speaker. Many thanks to R. Fesen, A. Soderberg, R. Margutti, J. Parrent, and L. Mason for helpful discussions and support Supernovae are among the mostbalance, global powerful structure, explosions and in chemical theholes, make-up and universe. some of gamma-ray galaxies, bursts, They they and affect theythe produce have the neutron accelerating been energy stars, used expansion as black of cosmological yardstickshowever, the remain to uncertain. detect universe. In this review Fundamental wein discuss properties understanding the supernova of progress progenitor made these systems over and the cosmic explosion lastanticipated mechanisms. two engines, future decades We directions also of comment on research andyoung highlight supernova remnants. alternative methods of investigation using ∗ † Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike Licence. c

during the preparation of this manuscript. Frank N. Bash Symposium 2013: NewOctober Horizons 6-8, in 2013 Astronomy Austin, Texas Harvard University E-mail: Dan Milisavljevic The Progenitor Systems and Explosion Mechanisms of Supernovae PoS(BASH 2013)009 ). 1 5 in . 7 − Dan Milisavljevic 2 Left: Hubble Space Telescope image of the Crab Nebula as observed in the optical. This is Supernovae are the energetic explosions of stars. They affect the energy balance, global struc- However, several fundamental questions remain regarding the nature of supernovae. Simple The earliest recorded Galactic supernova was viewed by Chinese astronomers in 185 AD and Centuries passed before one of the mostBrahe, famous only of Galactic 25 supernovae at was spotted the intoday time, 1572. made is Tycho detailed now observations known of as this event. Tycho’s supernova What remnant we see and in is this thought location to be the result of a Type Ia apparent visual magnitude. SN 1054 produced what we now observe as the Crab Nebula (Figure Figure 1: ture, and chemical make-up of the universe,dust, help produce trigger neutron star stars, formation, pulsars, are black holes, likelywith and a heavy some major elements gamma-ray source that bursts, of and make seed life the possible.cosmological universe distances They and are played also used an as importantis standard role accelerating. candles in in the determining discovery that the universe’s expansion questions such as “What stars explode?”Decades of and investigation “How have do shown stars that explode?”In there this do are short not review likely we have many attempt clear to channels tie answers. and to together explosion developments supernova related explosions. mechanisms to supernova made progenitor in systems with the historical last context, two then decades. explore presentend We understanding start with of with the anticipated an various topics types introduction of ofuncover informed future supernovae, powerful and investigation. information about Some supernova emphasis progenitorsobservations will and of explosion be young dynamics supernova placed remnants. from on detailed attempts to 1.1 Historical Context is now referred to as SN 185. The brightest ever recorded was SN 1006, which peaked at the remnant of thewavelength original composite image explosion of of Tycho’s1572. SN supernova Credit remnant. 1054. NASA/CXC/SAO (X-ray); NASA/JPL-Caltech This (Infrared); Credit: MPIA/Calar istical). Alto/Krause associated et NASA/ESA/J.Hester/A.Loll. al. with (Op- the Right: explosion of Multi- SN 1. Introduction Supernova Progenitor Systems and Explosion Mechanisms PoS(BASH 2013)009 – 5 400 ]. The 11 300 Ia Ib/c IIP IIL SN1987A Dan Milisavljevic Supernova Light Curves 200 daysmaximumafter light 100 ]. This confirmed predictions that 3 0 ]. A burst of neutrinos were detected a few 2 ] after decades of failed attempts, the closest

1 suspect/ which came from the original sources [

-20 -18 -16 -14 -12 absolute magnitude absolute ∼ 3 10000 ype IIype T ype Icype T ype IIbype T ype Ia ype SN SN 1999em SN SN 2004aw SN SN 1993J T ype Ibype T 9000 SN SN 2004dt SN SN 2008D Ca II 8000 O I 7000 He I Hα avelength [Å] avelength He I Optical Spectra Opticalof Spectra Supernovae Si Si II 6000 ). Brahe’s observations demonstrated that the “new star” did not move in its Rest Rest W 1 He I S II 5000 Left: Optical spectra of supernovae within weeks of maximum light. Data have been downloaded Fe II + Blend 4000 Ca II Modern classification of supernovae follows a spectroscopic system based on the lack or pres- The next well-observed, well-studied, nearby event occurred in the Andromeda galaxy in 1885.

]. Flux [Arbitrary Scale] [Arbitrary Flux 3000 ]. ]. Right: Representative light curves of supernovae during the first months after explosion. Adapted from 4 10 ence of spectral lines seen at optical wavelengths. The original system was proposed by [ 1.2 Supernova Classification most basic division is betweenassociated Type I with and hydrogen II and events. Type II Type I supernovae supernovae show lack clear conspicuous hydrogen features lines. Since Minkowski’s supernova in the era of modernand astronomy Oscar occurred: Duhalde at SN Las 1987A. Campanas Itthe Observatory was Tarantula in Nebula discovered Chile in by on the February Ian 24, Large Shelton hours 1987 Magellanic before in Cloud the [ visible outskirts light of from the supernova reached Earth [ It is referred to as SN 1885Aduring or the S age Andromedae. of the SN telescope 1885Ained reached and a only was magnitude monitored visually of closely. and 5.8. Spectroscopy no was Itthat photographic conducted occurred the but recordings exam- remnant remain. of A SN century 1885A later, was around discovered the by same [ time from the SUSPECT database at http://nhn.nhn.ou.edu/ supernova (Figure position for the months that itthat the was universe visible. beyond the He Moon argued and thatTycho’s planets observations this was and immutable was three was proof wrong. short that years Only thedetailed 32 after Aristotelian years observations his idea later of death, after the former assistant nextbeen Johannes recorded another Kepler Galactic Type made Ia supernova explosion SN and 1604. is observed This today is as Kepler’s believed supernova to remnant. have neutrino emission associated with core collapseincrease and in formation of visible a light neutron which star[ occurs preceded the only sharp after the shock wave breaks through the star’s surface Figure 2: 9 [ Supernova Progenitor Systems and Explosion Mechanisms PoS(BASH 2013)009 ] 22 Dan Milisavljevic Ni in the cascade 56 ]. Type I are divided 12 ] provided the framework ]). 18 19 ] and [ 10 ] found that the luminosity of the 21 representative light curves are shown. 2 ] were among the first to explain the ex- 17 . 2 4 7 Mpc) – the closest Type Ia supernova in 25 years – was ∼ ]. D 16 ] presented simulations of the explosion of a carbon white dwarf, and the 15 ]. They are observed in elliptical and spiral galaxies and thus associated with 15 Fe; [ – 56 13 → Co 56 → Some important papers include the following: [ Uncertainty in the progenitor systems of Type Ia supernovae is due largely to the fact that Approaching the issue of Type Ia supernova progenitor systems via a different route, [ Additional classification of supernovae can follow from the shape of its light curve. Type II Recent discussions of supernova subtypes can be found in [ Type Ia supernovae are thought to be explosions of degenerate carbon-oxygen white dwarfs. ]. Pre-explosion Hubble Space Telescope images of the region around the supernova did not Ni 20 looked at Hubble Space Telescope images of the central region of the supernova remnant SNR plosion of a Type Iof supernova understanding using the a light56 white curves dwarf via radioactive progenitor decay star; of [ freshly synthesized W7 model from this paper is a standard one still in use today (e.g., [ reveal an obvious progenitor star system. Using these images [ important as it provided[ one of the best opportunities to study the nature of Type Ia explosions young and old stellar populations. Twomerger progenitor of explosion two white scenarios dwarfs, are referred most todwarf often as that cited: a gains double 1) mass degenerate the (DD) from explosion, asingle or companion degenerate 2) (SD) main a explosion single sequence, white [ helium, or red giant star, referred to as a they occur at large distancesdiscovery of where SN it 2011fe is in impossible M101 to ( detect stars prior to explosion. Thus, the into three subclasses. Type Ia show Siblend II of features, lines as associated well with as iron-peak strongnot elements sulfur show including lines, strong calcium Fe lines, Si II and II, and a Co butshowing II. do weak Type show Ib or conspicuous supernovae lines absent do of features Heprofiles of I. of Si The H Type II Balmer Ic and class lines.times, He applies A but I for transitional objects Type in Ib class their features known spectra.weeks at as of late Type Type optical IIb II times. maximum show show are Example Type strong showed II spectra in P-Cygni features Figure of at various early supernovae obtained within 2.1 Progenitor systems progenitor system (especially the companionother star) Type Ia is supernova 10-100 progenitor times systems. fainter Thisgiants deep than and limit almost previous allowed all limits them helium to on stars rule as out the luminous mass-donating red companion to the exploding white dwarf. supernova may be classified as“linear” Type decline IIP in or the IIL months depending after on explosion. whether they In exhibit Figure a “plateau” or A runaway thermonuclear explosion isbinary initiated system as [ a result of mass transfer in some type of close Supernova Progenitor Systems and Explosion Mechanisms time, the binary classification hasface of branched new considerably objects and that is bridge subtypes being and continually extend updated luminosity ranges. in the The light curves of supernovaeof encode ejecta, information its about composition the and size density, and of the the supernova’s progenitor explosion star, energy. the mass 2. Type Ia supernovae PoS(BASH 2013)009 Ni and 56 4). They . 8 Ni and the ] to explore 56 30 = + Dan Milisavljevic V M ] concluded that PTF11kx ] are well-known examples 27 26 ]. 28 ] and SN 2005gj [ 5 25 ]. Using early-time data [ 27 ]. Transition from deflagration to detonation allows the star 29 50 yr ago. They found that the central region contains no ex- ± Ni. Alternatively, in a deflagration explosion the star does have time to 56 ] reported the spectroscopic detection of circumstellar material in a normal Type Ia 24 The nature of Type Ia explosions remains poorly understood. Scenarios of explosions proceed- A pure detonation explosion of a white dwarf proceeds faster than the white dwarf’s internal The best solution thus far has been to incorporate both explosion processes. One of the first SN 2011fe was discovered within 11 hours of explosion and was monitored closely thereafter Additional evidence for SD scenarios comes from examples of Type Ia supernovae that interact Considerable and equally compelling evidence for SD degenerate scenarios exists. For ex- ]. These exhaustive, high-cadence observations of SN 2011fe were used by [ ]). 20 23 whether they could bethree-dimensional used simulations to of constrain (i) Type Ia a supernova delayed explosion detonation scenarios in using a advanced Chandrasekhar-mass white dwarf ing via detonation (a super-sonic shockmodeled wave) with or only deflagration partial (a success. subsonic burning Thepure wave) problem detonation have is been or that a thermonuclear deflagration runaway do modelsor not involving yield the a light correct curves distribution that of agreeobserved with Fe-peak spectral photometric and observations observations. intermediate mass elemental abundances that match the sound speed. Thus,burning the shock star’s outer wave layers andelements, do the especially not swift have burning time nearly to completely expand converts or the react star to the into outgoing iron group proponents of this scenario was [ [ 2.2 Explosion mechanisms expand. Burning occurs insynthesis of lower more density intermediate mass material elements. and leads to less production of time to expand (during the initialof deflagration the phase) white resulting dwarf. in lower This,intermediate densities in mass in element turn, the abundances leads outer in to parts line less with complete early time burning spectral of observations. the outer layers into of this type of interaction.and exhibited PTF11kx the is interaction another stronglywas example [ that a was bona observed fide shortlyinterpretation Type after came Ia from outburst supernova late-time with data presented a in symbiotic [ nova progenitor. Further evidence for this with H-rich circumstellar material. SN 2002ic [ ample, [ supernova explosion. They foundcircumstellar that envelope the to expansion be velocities, consistent densities,system. with and the Relatively material dimensions low having of been expansion the dwarf ejected velocities was from of accreting the material the progenitor from circumstellarthe a material explosion. companion suggest star that that was the in white the red-giant phase at the time of Supernova Progenitor Systems and Explosion Mechanisms 0509-67.5 in the Largesupernova Magellanic that Cloud. took This place remnant 400 is believed to be the site of a Type Ia companion star to a visual magnitude limit of 26.9 (an absolute magnitude of claim that the lack of any ex-companionmodels star to for deep this limits rules supernova out and allbeen that published a single-degenerate the double-degenerate system. progenitor Objections of to[ this this interpretation, particular however, Type have been Ia made supernova (e.g., must have PoS(BASH 2013)009 ]. There 37 ] note that it 43 ]. The flux den- Dan Milisavljevic 46 ]. These fluctuations 42 ] and SN 2009bb [ 45 , 44 ], and SN 2003bg [ ]. A handful of progenitors of Type IIb have 41 33 6 ). They succumb to this violent death when nuclear

8 M , radio light curve variations are observed in a variety of ≥ 3 ], SN 2008ax [ 40 ]). ]. Most recently, high-resolution pre- and post-explosion images of 31 202 because it went against the theoretical expectation that Type II 35 ◦ ) and are not reviewed here. 1 69 − ] and [ − 19 ]. There have been unexpected discoveries with core-collapse progenitor stars. For ]. However, no detections so far have been conclusive. This lack of detection has been 32 38 However, it may be that less extreme mass loss episodes occur in a significant fraction of 1 SN 2009ip was a Type IIn supernova. Type IIn supernovae are associated with narrow spectral features (full width Many supernovae show evidence for episodic mass loss prior to explosion. An extreme case Real progress has been made in the last twenty years with regard to the progenitor systems The progenitor stars of Type Ib and Ic supernovae have been difficult to find. They have been It is thought that the spectral classifications of Type II, IIb, Ib, and Ic may follow an order Type Ib, Ic, and II supernovae occur exclusively in spiral galaxies and are generally associated 1 ]. ]. 39 36 at half maximum < 200 km s have been possible detections of progenitorexample stars [ of of Type Ib supernovae; iPTF13bvn is a recent is intriguing how the radio modulationsincluding have the also gamma-ray been burst-associated observed SN in 1998bw [ relativistic, engine-driven SNe is SN 2009ip, which was[ a supernova that interacted withprogenitor an systems. extensive circumstellar As environment seen in Figure also been imaged. Theassociated first, with before a the K0I star Hubble [ Space Telescope era, was SN 1993J, which was used to argue that these supernovae should originate from moderate mass interacting binaries. instance, it came assupergiant something Sanduleak of a surprise that the progenitor star of SN 1987A wasof the core-collapse blue supernovae thanks inTelescope. large Pre-explosion part images to ofsome high Type progenitor resolution II events images systems do of come has from the established red Hubble supergiants fairly [ Space well that at least theorized to be Wolf Rayet stars since they can be largely devoid of H-rich envelopes [ supernovae come from red supergiants. the region around the Type IIb SN[ 2011dh demonstrated that its progenitor was a yellow supergiant supernovae including SN 2001ig [ are similar in both timescale and amplitudemodulations and in have the been reasonably pre-explosion explained environment in shaped terms of by density the progenitor system. [ sity modulations in these cases were attributed to energy injection from the central engine, but the consistent with the progenitor stars havingenvelopes been [ increasingly stripped of their outer H- and He-rich fusion suddenly becomes unable to sustain theof core heavy against elements its own in gravity the and universe. are a primary source 3.1 Progenitor systems with the core-collapses of massive stars ( Supernova Progenitor Systems and Explosion Mechanisms and (ii) a violent merger ofnot two found white (see dwarfs. also A [ clear preference for one model over the other was 3. Type Ib, Ic, and II – Core-collapse Supernovae ; 1 ), ), × − 5 . ). ,and )and 1999 2 ˙ 2006 2006 % M 5.2 ∼ M ,forwind counts s 1 k 4 ). A low Ni − E 15 − . yr 0 10 % ;Woosleyetal. 2011 as expected from ! and 3asindicatedby ), and thus are in × Milisavljevic et al. ). Lower-mass He 2 M 9 6 % − . 4 = for SN 2011ei is on 1990 − R immediately prior to M ). The helium and iron ;Hamannetal. p 1991 ), (2) a power-law elec- 1 % 10 6 ∝ % . − 1 × M M yr 1991 2 with 2006 CSM ∼ 1 % . 04 ρ 1asindicatedbywell-studied p . . 0 M ej − 0 0 e ˙ < M< 6 γ ). Given these assumptions, the ≈ M 0 − = .Thiscalculationisconsistentwith n e 1 10 " − ;Taubenbergeretal. 2006 = ;Hachisuetal. 10 (see, e.g., Matzner & McKee % ! 6. DISCUSSION (Shigeyama et al. ) e ), (3) the radio-derived mass-loss rate of ˙ M cm) is consistent with those of W-R stars ∼ γ % M ( in an interacting binary system. ,oralower-massstarwithmain-sequence 1990 11 n M 15 N ! % % . 1991 ). The putative W-R star could have evolved 10 4 6.1. The Progenitor of SN 2011ei 1000 km s M M − 3–4 × with = ), we estimated the progenitor mass-loss rate via 05–0 ), (2) some subtypes of W-R stars (e.g., the WN 2007 . 25 ∼ 1 n w PoS(BASH 2013)009 0 − upper limit on X-ray emission of 7 ∼ v ! ∼ R 10–15 2012 2003 ∗ ∼ erg), and adopting the formalism discussed in Margutti ). The initial presence and subsequent rapid disappearance ∝ R Several properties of W-R stars make them plausible candi- Using the reconstructed bolometric luminosity and the de- The early onset of helium-rich features in the optical spectra Our inferred Ni mass of 51 SN W-R stars (10 SN 2011ei is consistent with the observed rates for Galactic expansion velocities determinedto from our SN synthetic 2011ei spectral areagreement quite fits with the similar emitting (see ejecta Figure being well mixed. date progenitors for SNbe 2011ei: likely (1) progenitors W-R ofet stars at are al. least believed some to class) SNe have IIb an and observable amount Ibc(Hamann of (Heger et hydrogen at al. their surfaces stars are also predicted tohigher-mass stars undergo do more (Hachisu extensive et mixing al. than tron distribution hydrogen envelope of mass 1995 of hydrogen suggests the progenitor star still retained a thin X-ray IC. Werelativistic assumed electrons (1) was the fraction of energy going into velocity tribution responsible for the up-scattering,any but assumption does on not magnetic require not field affected by related possible parameters uncertaintieslimits on and the on it SN X-ray distance. is Thus, emissionSN mass-loss can history provide of the information progenitoranalysis. on independent of the our radio pre- rived explosion parameters ( 10 the low end ofevents Ni ( masses derived for other stripped-envelope eject considerably less material than do(Shigeyama their et larger counterparts al. explosion. Chandra the properties derived from our radio analysis (Section of SN 2011ei and theconsistent evolution with of its model bolometric explosions light ofmasses curve He-core are of stars with pre-SN mass yield is consistentstar with the progenitors explosions that of have lower-mass He small iron cores ( SN shocks (Chevalier & Fransson astarwhichhasbeenlosingmaterialatataveragerate (4) that theρ outer density structure of the ejecta scales as and (4) the progenitortry radius ( inferred from the early photome- mass et al. ( (Crowther originally from either amass single of star with a high main-sequence in the 0.5–8 keV band implies radio observations of(3) SNe a wind-like Ibc CSM that (Chevalier follows & Fransson Chevalier & Fransson .A 3 − 15 g cm ) ), 3 14 ∼ -axis Dan Milisavljevic ). In x ), and 10 2004 1999 × 5 2009 2006 − ). Bottom 1998 -axis represents inferred -axis represents days since supernova .Inparticular,allofthese x x 1 − ). Nuclear binding energy per nucleon ]. The process is thought to start with t ;Li&Chevalier ). In these cases, the flux

49 ∝ ν 5 M F . 1998 1 cm may be common among stripped-envelope 2010b )yrpriortooutburst. ] and [ ∼ 17 1 7 ), the optically thin synchrotron 48 − 10 ). All exhibit variable radio emission that deviates from ), SN 2008ax (Roming et al. ]. ;Chevalier&Fransson 1 . − 43 2012 km s 2006 ,767:71(19pp),2013April10 3 2004 10 . From [ 3. Thus, assuming a constant compression / 1 1000 km s − w t = = v cm. Attributing this effect to a variation in ∝ ). Each of these SNe shows variable radio emission that w 1 p ν v 7( − F 2jumpinthecircumstellardensityataradius 16 ∼ ∼ for 10 that has undergone successive stages of hydrogen, helium, carbon, neon, cm may be common among stripped-envelope SN 2 e 5 GHz light curve for SN 2011ei is compared to those of other

n × -axis represents inferred times of circumstellar material density modulations in years 17 5.3. Limits on Inverse Compton X-Ray Emission x ∝ 2 8 M 1000 km s 10 ν > = ! ] who first proposed that supernovae are energized by the collapse of an ordinary star F ∼ ¨ For hydrogen-stripped SNe exploding in low-density environ- It is intriguing to note that radio modulations have also We adopt a model in which the modulations in the radio light ornsson & Fransson w 47 this framework, X-ray photons originateof from the optical up-scattering photonsof from electrons the accelerated SN toX-ray relativistic photosphere speeds IC by by depends a thethe SN on population shock. structure the of density the structure CSM, of and the the details SN of ejecta, the electron dis- and SN 2009bb (Bietenholz et al. ments, the dominant X-ray emission mechanismweeks during to the a first monthBj after the explosion is inverse Compton (IC; emission scales with theas number density of shocked electrons of been observedGRB-SN in 1998bw (Kulkarni relativistic, et al. engine-driven SNedensity including modulations havefrom been the attributed central tothe energy engine. observed injection However, compact given progenitorwe the Type speculate IIb resemblance that radio to modulations, CSM density fluctuations on radial scales the GRB-associated Type Ic SNrepresents 1998bw days (Kulkarni since et supernova outburst, al. and the top factor by thedensity forward modulations scale shock, similarly. we Given find the that factor the of circumstellar explosions. curve are similarly dueshown to in circumstellar Wellons density et variations. al. As ( events show second maxima within a few(A months color of version the of explosion. this figure is available in the online journal.) deviates from the expected decay as roughly Figure 18. radio supernovae includingSN the 2003bg Type (Soderberg IIb et SNe al. 2001ig (Ryder ettimes al. of CSMv density modulations in years previous to outburst (assuming The Astrophysical Journal the progenitor wind oftimescale of the progenitor star implies an ejection in flux density modulationsafactorof observed for SNr 2011ei, we infer The 5 GHz light curve for various supernovae. Bottom The explosion that is predicted to follow is not well understood. Collapse halts when the It was [ repulsive component of the nuclear force kicks in at densities around 4 a massive star oxygen, and silicon fusion attotal its mass core. that Eventually, exceeds a the core Chandrasekharreaches of limit Fe-group maximum ( elements at is the produced Fe-group,high with temperatures so a and no densities induce further electron energyof capture can electrons by robs nuclei be the and released core photodisintegration, by of the crucial loss nuclear pressure, fusion. and the The iron core collapses. to a neutron star. Since then,can hundreds work of studies in have detail; attempted pioneering to understand papers how include such [ a process the expected decay as roughly resemblance to radio modulations ofin non-relativistic circumstellar supernovae material suggest on that radial density scales of fluctuations Figure 3: outburst and the top previous to outburst (assuming supernova explosions. 3.2 Explosion mechanisms rebound generates a shock wave as the outer half of the core continues to crash down. It was long- Supernova Progenitor Systems and Explosion Mechanisms PoS(BASH 2013)009 – 60 range) the

Dan Milisavljevic 10 M − ]. Additional clues for 69 – 65 ]. The shock wave stalls because of continued 8 53 – 50 ], and the influences of rotation and magnetic fields [ 59 – 54 6 months beyond outburst in stripped-envelope events often exhibit multi- > ]. t 71 , 70 Left: Multi-wavelength composite image of the O-rich, Galactic supernova remnant Cassiopeia A. An alternative way to investigate core-collapse supernova explosions is through observations Many studies have explored a variety of possible mechanisms by which the stalled shock can Observations of the kinematic and chemical properties of supernova ejecta can help investigate ]. of young supernova remnants.kinematic asymmetries Studies in of the young expandingextragalactic ejecta O-rich observations. at Galactic spatial They remnants and candistinct allow kinematic zones also one scales in offer the not to progenitor clues possible probe star about from and the the nature explosive of mixing the central of compact chemically remnant. constraining explosion mechanisms come from spectropolarimetry.can These be studies asymmetric show that in ejecta theaspherical inner [ layers, supporting the view that the explosion process is4. strongly Young Supernova Remnants be re-invigorated. Aspericity in theexpansion asphericities explosion is appears currently uncertain. to Possible be causesand of include accretion-shock asymmetric crucial instabilities neutrino importance. heating [ The origin of photodisintegration and copious neutrino losses.motion A stops few and milliseconds the after dense, the hot bounce neutron-rich the core outward begins to rapidly accrete in-falling mass. which of the aforementioned explosion mechanismsspectra may dominate. obtained For example, late-time optical peaked emission line profiles consistentexplosions viewed with along aspherical different axisymmetric angles from and the potentially equatorial jet-related plane [ 64 Figure 4: Optical data obtained with the Hubble Spaceand Telescope, X-ray near-infrared with data with the the Chandra SpitzerCassiopeia X-ray Space A Observatory. Telescope, made Credit: from NASA/JPL-Caltech. X-ray data. Right:high-velocity material Credit: Enhanced in Si NASA/CXC/GSFC/U.Hwang the et image NE al. of and The SW outflows regions (or are ‘jets’) labeled. of believed that this bounce-shock mechanism might bemodern the simulations driver of have supernova explosions. demonstrated However, that (at least for stars outside the 8 Supernova Progenitor Systems and Explosion Mechanisms outgoing shock is not energetic enough [ PoS(BASH 2013)009 Dan Milisavljevic ]. At an estimated ] enabled follow-up 72 78 – 76 upon explosion, leaving behind

4 M ]. This may have required the existence − 74 ). With an explosion date most likely around 4 9 ]. 75 progenitor to only 3

25 M − ], it is also among the closest. Cas A is inferred to have undergone extensive ] showing the kinematic map constructed for Cas A. Top: Locations of over 200 slit 73 80 Data from [ ]. The young Galactic remnant Cassiopeia A (Cas A) provides perhaps the clearest look at the Cas A is the only historical core-collapse supernova remnant with a secure supernova subtype 77 , 79 mass loss from its original 20 a relatively dense and slow moving remnantof stellar wind a [ binary companion to aid the mass loss [ optical spectral observations that determinedspectrum at the maximum original light supernova similar to to[ those have seen exhibited for the an Type optical IIb events SN 1993J and SN 2003bg explosion dynamics of a high mass supernova (Figure classification. The detection of light echoes of the supernova outburst [ positions used to develop a 3Darrow reconstruction. points to Bottom: a Various region perspectives coincident of with the X-ray resulting emitting 3D Fe-rich map. material. Blue 4.1 Cassiopeia A Figure 5: 1680, Cas A is the youngest Galacticdistance core-collapse of supernova remnant 3.4 known kpc [ [ Supernova Progenitor Systems and Explosion Mechanisms PoS(BASH 2013)009 0 4 10 degrees) ). Its optical- < 5 (0.5 pc) and 2 Dan Milisavljevic 00 3 2 1 0 X 10 −1 ]), but still puzzling because their chemistry is consistent 61 ) material. Previous studies could not address the question of , 1 − −2 60 , 81 km s 4 −3 10 the optically-emitting S-rich and O-rich main shell ejecta are shown along × 7 5 . 1 , a Mercator projection of the main shell knots is shown to illustrate the relative 6 0 2 1 − −4 −2 −1

0.5 1.5

−0.5 −1.5 Y The main shell of Cas A’s optically-emitting ejecta as represented in a Mercator projection. From ] recently created a detailed 3D kinematic reconstruction of Cas A (Figure 80 The important lesson from Cas A is that the distribution of its metal-rich ejecta is not random. Motivation to undertake a deep reconnaissance of the entire Cas A was driven in part from [ ]. 80 jet-induced explosion (e.g., [ The sizes and arrangement of theof large-scale rings the may explosion be dynamics informing and usiron about subsequent – important evolution properties which of is the a expandingintriguing. good debris. In tracer The Figure of distribution the of explosion dynamics – with respect to the main shell ejecta is whether they form a truebe bipolar directed structure. in nearly TheThis survey opposite makes demonstrated directions the that with outflows the opening inconsistent outflows half-angles with appear a of to highly-collimated approximately (opening 40 half-angle with degrees. an origin from the Si-S-Ca-Ar layer deep within the progenitor star. an interest in finally grasping thehigh kinematic velocity properties (1 of the NE and SW regions of exceptionally scale and distribution of the rings.circles Some or rings ellipses. form complete circles, while others appear as partial Figure 6: [ emitting ejecta were mapped fromtaken a over several spectroscopic years and survey represents involving the hundreds mostthe complete of optical kinematic to long map date. slit of a The spectra supernova reconstructionwell-defined remnant shows in and that nearly Cas circular A’s main rings shell(2 ejecta with pc). are diameters In arranged between Figure in approximately several 30 Supernova Progenitor Systems and Explosion Mechanisms ) ). ives

PoS(BASH 2013)009 blue 2010 2006b ! l. M ). As shown ] 85 2010 N Obs Milisavljevic & Fesen ) have investigated 2001 E Dan Milisavljevic data presented in ] and X-ray data are from 80 Chandra ), it is still tempting to draw an association 2012 Ni-rich ejecta, ultimately giving way to a “Swiss )andBlondinetal.( 56 1994 ]. However, there are difficulties with invoking a Ni bubble The turbulent motions that would initiate this Ni bubble 84 turned over with nickel-dominatedrich fingers overtaking bullets. oxygen- Althoughstrongly dependent on the the internal structure evolution of the(Ugliano progenitor of et star al. thesebetween simulations the is Ni-rich outflows seenmodels in and the the rings Hammer of et Cas al. A. ( picture to explain how theby X-ray emitting rings Fe ejectaeffect of should are be framed optical characterized by diffuse ejecta. morphologies and low Fe associated with the bubble supergiant star presented inin Hammer their et Figure al. 2, ( the progenitor’s metal-rich core is partially cheese” ejecta structure. It is important toejecta note that structures the are main shell observed asthe rings reverse because shock we that are only biased excitesit by a is thin shell reasonable of to material.sections Thus, suspect the of observed what ejecta arebubbles. rings actually to be larger cross spherical geometries, i.e., structure in Casthe A large-scale are mixingstellar not that layers unlike takes recent ejected place 3D in in simulations the the of explosion shock-heated of a 15.5 hydrodynamic simulations basedconsequence on of this this scenario model. isnon-radioactive the One material compression by possible of the surrounding rising andradioactive expanding bubbles of filling factor ofBasko Fe in ( SN 1987A despite its small mass, and 10 11 Ni-rich ejecta [ 56 )havedescribed 1993 S P data presented in DeLaney X Chandra ,772:134(15pp),2013August1 )notedthecoincidenceoflargeejecta Left: Vector plots of the high velocity ejecta knots (colored green and blue, respectively) shown Obs N 2010 ,weshowtheopticallyemittingmainshell Recent 3D reconstructions of other young core-collapse supernova remnants have suggested Indeed, direct connections between Cas A and extragalactic supernovae have been made. [ The ejecta rings are not unlike large-scale features seen in supernova explosion models (e.g., Ni-rich ejecta. Li et al. ( ]) and may have origin in part to a “Ni bubble effect” having influenced the remnant’s expansion ]. Interestingly, each of the three large concentrations of Fe-rich ejecta lie within and bounded ]. 10 ). An animation showing these data sets rotated 56 E ). 83 82 82 summed all main shellwould spectra appear into as as a an single,between unresolved integrated the extragalactic source. integrated spectrum, Cas Intriguingly, mimicking A close spectrumgalactic what similarities supernovae, and were the including several found SN remnant late-time 1979C, SN optical 1993J, spectraremnant SN of in 1980K, NGC decades-old and 4449. the extra- ultra-luminous These supernova ous spectra line all substructure showed in pronounced oxygen, blueshifted sulfur, and emissionin argon. Cas with A Because conspicu- is the associated emission with line large-scale substructureobserved rings observed in of intermediate-aged ejecta, supernovae it are is possible also that associated the with similar large-scale line rings substructure of ejecta. that many of the kinematicful properties of observed known in supernova Cas remnantsstudied A are have are appropriate not revealed for unique. evidence thishigh-velocity of Although kind bipolar the only of asymmetries a same analysis, as hand- large-scale those observedmay ejecta have that in implications have Cas rings, for been A. a velocity variety Thus, asymmetries, of information supernovae and and learned supernova from remnants. Cas A 4.2 Broader Implications [ dynamics shortly after the originalrepresent explosion. cross-sections of Indeed, large it’s cavities possible inof the that energy expanding from the ejecta plumes observed created of ejecta by radioactive rings a post-explosion input with the location of X-ray[ emitting iron-rich material measuredby ring from structures. This complementary arrangement is consistent with a causal relationship. Figure 7: along with the mainrespect shell to the (colored main red). shell sulfur- and Right: oxygen-rich ejecta. Location Optical of data are iron-rich from X-ray [ emitting ejecta (blue) with Supernova Progenitor Systems and Explosion Mechanisms [ Vector plots of all NE and SW ejecta knots (colored green and blue, respectively) shown together with the main shell ejecta (red). Four angled perspect 2010 ISM environment. The optical data presented here do not 1987 ) that we favor is that the observed ejecta rings represent / In Figure An alternative explanation first suggested by Blondin et al. DeLaney et al. ( 2001 CSM alter this overall picture, but provide anexamination improved, more of detailed Cas A’s expansion properties. (An animation and a color version of this figure are available in the onlinethat journal.) are relatedfield to and independent the of any true strong structure influences of of the remnant’s the remnant’s debris Figure 9. are shown with the upper leftRefer being to as Movie seen 2 in for the an sky. A animation black of arrow these shows data. the inferred motion of the XPS with respect to the center of expansion (Fesen et a The Astrophysical Journal how this input of energy might account for the high-volume radioactive ( cross-sections of large cavitiesin in the part expanding by ejecta created a post-explosion input of energy from plumes of represent the intersection points of these pistonsshock, with similar the reverse to theet bow-shock al. structures ( described by Braun that these and otherthe less ejecta have prominent emerged from features the explosion arethan as “pistons” average regions of ejecta. faster where In this view, the remnant’s main shell rings and bounded byrelationship. ring structures, strongly suggesting a causal rings with the three regions of Fe–K X-ray emission and argued about the north–south(Movie and 3). east–west Each axes ofejecta has (i.e., the along the three been west, north, largest and provided southeast concentrations limbs) lies of within Fe-rich ejecta alongmaterial with measured the from et location al. of ( X-ray emitting iron-rich PoS(BASH 2013)009 Dan Milisavljevic ]. The observed inhomogene- 88 – supernova per year, and Advanced 86 5 10 ∼ 12 5 mag to find . 24 ∼ r Supernovae, 200 Astronomical Society, 371, 1459 1490 Fundamental questions remain about the nature of supernova progenitor systems and explo- Real progress has been made with the progenitor systems of core-collapse supernovae. Direct Looking further into the future, new facilities promise to revolutionize the field of transient as- [7] Modjaz, M., Li, W., Butler, N.,[8] et al. 2009,Matheson, Astrophysical T., Filippenko, Journal, A. 702, V., 226 Barth, A.[9] J., etHamuy, al. M., 2000, Pinto, Astronomical P. A., Journal, Maza, 120, J., 1487 et al. 2001, Astrophysical Journal, 558, 615 [4] Burrows, A., & Lattimer, J. M.[5] 1986, AstrophysicalAltavilla, Journal, G., 307, Stehle, 178 M., Ruiz-Lapuente, P.,[6] et al. 2007,Taubenberger, S., Astronomy Pastorello, and A., Astrophysics, Mazzali, 475, P. 585 A., et al. 2006, Monthly Notices of the Royal [1] Fesen, R. A., Saken, J. 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With regard to Type Iasingle-degenerate explosions, and the double-degenerate pendulum progenitor swings systems back [ and forth between imaging of supernova progenitor systemscan has come demonstrated from convincingly red that supergiant Type stars.Ib, II The and supernovae progenitors Ic of have stripped-envelope been supernovaesion more of mechanisms difficult Type may IIb, to await understand. the next Detailedyoung, generation understanding nearby of of supernova sophisticated core-collapse remnants 3D can explo- simulations. provideand Investigations unique local of environments information of about supernovae the that explosion will dynamics provide constraints for these simulations. tronomy. The Large Synoptic Survey Telescope willnights image with the a entire available single night visit sky depth every few of Supernova Progenitor Systems and Explosion Mechanisms 5. Conclusions ity of these events has leddetonation-to-deflagration to model the growing is speculation currently that the twodo best or so at more for channels reproducing all all empirical observables contribute. and results, the The but physical cannot motivations behind this scenario are not well understood. LIGO, which is sensitive togular gravitational momentum, waves nuclear that equation carry of livenovel dynamical state) probe information from of (mass, the deep an- core-collapse insideupcoming supernova the decade explosion supernova will mechanism. core, explore will uncharted Thesea frontiers provide and little of a other luck) high efforts will energy, shed of extreme new the astrophysics light and on (with supernovae. References PoS(BASH 2013)009 Dan Milisavljevic 13 Society, 349, 1093 1005 Supernova Progenitor Systems and Explosion Mechanisms [13] Hoyle, F., & Fowler, W. 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