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A Million Second Chandra View of Cassiopeia A

A Million Second Chandra View of Cassiopeia A. Una Hwang (NASA/GSFC, JHU) & J Martin Laming (NRL). Boston AAS 24 May 2011. Cassiopeia A Core-collapse SNR with the most prominent Fe ejecta emission. Si and Fe distributions are distinct (Hughes+ 2000, Hwang+ 2000, Willingale + 2002)

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A Million Second Chandra View of Cassiopeia A

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  1. A Million Second Chandra View of Cassiopeia A Una Hwang (NASA/GSFC, JHU) & J Martin Laming (NRL) Boston AAS 24 May 2011

  2. Cassiopeia A Core-collapse SNR with the most prominent Fe ejecta emission Si and Fe distributions are distinct (Hughes+ 2000, Hwang+ 2000, Willingale+ 2002) Advanced evolutionary state: reverse shock has heated a substantial portion of ejecta (Laming & Hwang 2003, Chevalier & Oishi 2003) Cas A First-light Chandra image (Hughes+ 2000) Red: Fe, Green: Si Best studied SNR at all wavelengths Explosion date: 1671 (to 1681; Thorstensen+ 2001, Fesen 2006) Distance: 3.4 kpc (Reed+ 1995) Shock velocities, radii (Gotthelf+ 2001, DeLaney & Rudnick 2003; Helder & Vink 2008, Morse+ 2004)

  3. Krause+2008 Infrared light echo spectrum: Cas A was Type IIb (core-collapse with partial H envelope) Extensive progenitor mass loss: Aided by a binary companion (Young+ 2006) SNR expansion into circumstellarwind matches dynamics (Laming & Hwang 2003, Chevalier & Oishi 2003) CSM modified by bubble (Hwang & Laming 2009) or dynamics modified by particle acceleration(Patnaude & Fesen 2009) Shocked CSM mass: ~10 Msun Likely mass at explosion: ~ 4 Msun (Willingale+ 2003, Laming & Hwang 2003, Chevalier & Oishi 2003)

  4. XMM-Newton spectral survey of Cas A Willingale+2002, 2003 15x15 grid two component fits Total mass: 2.2 Msun ejecta 7.9 Msun CSM

  5. Cas A X-ray Emitting Ejecta Census 1 million second VLP observation with Chandra ACIS 2004 nine OBSIDs 2.8x108 photons 6202 extraction regions: 2.5, 5, or 10” along one side customized spectral response off-source background scattered source spectrum selected by azimuth Plane-parallel shock model with variable abundances, elements O and heavier

  6. Cas A Chandra Fitted Element Abundances

  7. Classify each region by dominant spectral type Possible contributions to each spectrum include: forward shocked thermal emission from CSM nonthermal emission reverse shocked thermal emission from ejecta Eliminate 1500 forward shock/nonthermal dominated regions: plane-parallel shock with CSM-type abundances optional power-law Consider >4000 remaining regions as ejecta: plane-parallel shock with O as lightest element

  8. Gallery of Spectral Types Normal CSM Fe dominated ejecta Nonthermal (not NS) “Normal” composition O, Ne, Mg, Si, etc Mixed ejecta “Normal” and Fe rich Mixed CSM nonthermal Two ejecta components: “normal” + pure Fe (see also Hwang & Laming 2009)

  9. “Pure” (very highly enriched) Fe Ejecta Chandra 50 ks (BG subtracted) Hwang & Laming (2003) Fe/Si > 16 solar by # Plausible site of -rich freeze out (products include Fe, 44Ti, ) src+bg src Chandra Ms (BG modelled) Fe/Si ~ 20 solar by #

  10. Ejecta Mass Calculations Ejecta fits with (1) single vpshock or (2) vpshock + NEI (Fe, Ni only): evaluate with f-test Use fitted emission measure assume V=A2/3 filling factor for 2.5” shell front and back Total shocked ejecta mass = 2.8 Msun Mostly O (2.55 Msun) Fe= 0.10Msun(normal Si-burning) +0.04 Msun(pure, a-rich freezeout) (Chevalier & Oishi 2003) Narrow density peak at contact discontinuity Total ejecta mass = 3.1 Msun Unshockedejecta mass = 0.3 Msun

  11. Unshocked ejecta is probably Si Infrared observations show unshockedejecta at remnant center, primarily in [Si II] Little optical or infrared evidence for Fe (Ennis+ 2006, Rho+ 2003, Isensee+ 2010, Hurford & Fesen 1996, Gerardy & Fesen 2001) Cool 35 K dust component consistent with Si (Nozawa+ 2010; Sibthorpe+ 2010, Barlow+ 2010) Radioactive heating of Fe ejecta by 56Ni decay inhibits Fe dust condensation Condensation less efficient in IIb events vs those without mass loss Spitzer Observatory Smith+2009, Rho+2008

  12. X-ray inferred mass of shocked Fe is 0.088 – 0.14Msun depending on assumptions consistent with expected mass of Fe 0.058-0.16 Msun (Eriksen+ 2009) Fe associated with low or high Si about evenly (consistent with Magkotsios+ 2010) All the Fe ejecta are found well outside the center 44Ti associated with pure Fe will also be outside the center small LOS velocity (INTEGRAL; Martin & Vink 2008, Martin+ 2009) may be tested with NUSTAR Two other remnants with 44Ti are different from Cas A: SN 1987A : all the 44Ti are in the center (Kjaer + 2010) G1.9+0.3 : most of the 44Ti are outside (Borkowski+ 2010) Strong instabilities must operate to mix the Fe far outwards

  13. Neutron Star Kick Neutron star speed is inferred to be 330 km/s, roughly perpendicular to axis of ejecta “jets”, fast optical knots Hydrodynamical simulations (3D, non-rotating progenitor; Wongwathanarat+2010): Predict NS recoil opposite maximum explosion strength (ie, opposite the Fe?) Velocities of 1825 optical knots (Fesen+ 2006) Inferred motion of NS (Thorstensen+ 2001)

  14. Fe ejecta • Due east • Between NS motion and jet • All ejecta • East of North • 700 km/s • 150 degrees from NS motion • Remnant as a whole moves opposite to NS: • Suggests hydrodynamic origin for NS kick NS motion

  15. Three Dimensional Structure of Cas A DeLaney+ 2010 3D structure from Doppler shifts: Infrared [Ar II] (Spitzer) High [Ne II]/[Ar II] [Si II] X-ray Fe K (Chandra Ms) outer optical knots (Fesen 2001, Fesen & Gunderson 1996) Si/”Mg” ratio Si in center, in rings on the surface Fe ejecta, high-velocity “jets” in outflows encircled by outlying material

  16. Summary 3 Msunejecta is inferred from census of X-ray emission and is also consistent with the observed remnant dynamics Most of the Fe ejecta is already shocked, and sits well outside the reverse shock; some of the Fe is “pure” 44Ti is expected to have the same distribution as pure Fe Long exposure crucial to find pure Fe via Fe K emission Inferred momentum of Fe ejecta is perpendicular to the jet axis, not opposite the NS; momentum of total ejecta opposes NS Hydrodynamic mechanism for the kick looks likely Cas A provides constraints on hydrodynamics of the explosion and is ripe for targeted explosion models including progenitor rotation

  17. Abstract Deadline: 31 May 2011

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