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					Constraining progenitors of
    SNRs using X-ray
 morphology and spectra
          Hiroya Yamaguchi
Harvard-Smithsonian Center for Astrophysics
          Classification of SN Progenitors
Optical obs of SNe
Classification is relatively
straightforward
- Spectrum (historically
   well established)
- Luminosity (56Ni yield)



X-ray obs of SNRs
                                          Ia (SD)
Classification (Ia/CC) is (was)
controversial in many SNRs
                                                        Ia (DD)              CC (1987A)
- Similar X-ray luminosity
                                      SNe Ia: nuclear reaction energy ~ 1051 erg
- Morphology?
  SNRs can be spatially resolved,     SNe CC: gravitational energy ~ 1053 erg
  strong advantage of X-ray                   99% neutrino + 1% kinetic (~ 1051 erg)
- Spectrum?                         => transformed to thermal energy (X-ray luminosity)
                                Morphology of SNRs
                  CC SNRs are more asymmetric than Ia SNRs (Lopez+09;11)


                 CC     0104-72.3




                  E0102-72
Ellipticity




                Type Ia                      Chandra images of Galactic/Magellanic SNRs

                                               Doesn’t work for SMC SNRs… (Lopez+12)
                  Mirror asymmetricity
              Reflects nature of explosion
                and/or environment?

   G344.7-0.1 found to be Type Ia (HY+12)
                                                SNR E0102-72 (CC)   0104-72.3 (Ia candidate)
                  X-Ray Spectra of SNRs
Advantage
 - Optically thin (self absorption is almost
    negligible, but see Miyata+08)
 - K-shell emission from He- & H-like atoms
    (kTe ~ hn ~ 0.1–10 keV, comparable to
     K-shell potential), so physics is simple
                           YOU LOSE                    Suzaku spectrum of
                                                       Tycho (Hayato+10)

Simple Quiz                m9(^Д^)
                                                                  S   S Ar        Fe
                                                                             Ca
                                                                  i
                                                Artificial
                                                 features
                                                (a sort of bgd)
                                                                                   Ni
        Ia (SN1006)                                               CC (W49B)
                                                             Mg

                                                       Ne
 X-Ray Spectra of SNRs
                          Large foreground extinction makes
    Absorption for        O/Ne/Mg emission in W49B weak
    different column
                           Note: although we use NH to describe
    density (NH [cm-2])    the column, what we measure in
                           X-rays is the column of metals
SN1006
                           Yet, weakness of Fe emission in
                           SN 1006 (Ia SNR) is puzzling
                             => Understanding of NEI
                                 is essential

                                              S   S Ar        Fe
                                                         Ca
                                              i
             W49B           Artificial
                             features
                            (a sort of bgd)
                                                               Ni
                                              W49B (CC)
                                         Mg

                                   Ne
                 Non Equilibrium in Ionization (NEI)
                                                                     Pre-shocked metals in ISM/ejecta
                                                                     are almost neutral (unionized)

                                                                     Shock-heated electrons gradually
                                                                     ionize atoms by collision, but
                                                                     ionization proceeds very slowly
                                                                     compared to heating


                                                                            Fe16+        Fe24+        Fe26+
               Fe ion population in NEI plasma for kTe = 5 keV                                Fe25+
                   lowly      Fe16+     highly
                    ionized             ionized      Fe24+
                                                                                                      CIE
Ion fraction




                                                         Fe25+
                                                                        Electron temperature kTe (keV)


                                                             Fe26+    net : “ionization age”
                                                                       ne : electron density
                                                                       t : elapsed time since gas was heated
                                      net (cm-3 s)
                 Non Equilibrium in Ionization (NEI)
               Fe ion population in NEI plasma for kTe = 5 keV
                                                                     net : “ionization age”
                   lowly      Fe16+     highly                       ne : electron density
                    ionized             ionized      Fe24+           t : elapsed time since gas was heated
Ion fraction




                                                         Fe25+
                                                                     Timescale to reach CIE for ISM
                                                                       t ~ 3 x 104 (ne/1 cm-3)-1 yr
                                                             Fe26+


                                      net (cm-3 s)
    As for ejecta…
    Time when the masses of swept-up
    ISM and ejecta becomes comparable

                                                         Ionization state for the ejecta becomes almost
                                                          “frozen” after an SNR evolved.
                                                         Ionization age for the ejecta strongly depends
                                                          on the initial CSM density rather than its age.
          Non Equilibrium in Ionization (NEI)
      How does ionization age affect a spectrum? How can we measure ionization age?
                             Model spectra of Fe emission [kTe = 5 keV]
      net = 5x109            1x1010           5x1010            1x1011     3x1011

                                       Fe-K

                          Fe-L blend
  Full X-ray band
0.5                 10
  Magnified spectra in the 6-7 keV band (Fe K emission)                    He-like
                                              C-like             Be-like
    Ar-like              Ne-like
                                                                                     H-like


6.0                 7.0
  Observed spectrum (Convolved by Suzaku response)




      6.42 keV             6.44 keV           6.60 keV          6.64 keV    6.67 keV
SN1006 (Type Ia SNR)    W49B (CC SNR)




                                         S   S Ar        Fe
                                                    Ca
                                         i
                       Artificial
                        features
                       (a sort of bgd)
                                                          Ni

                                    Mg

  HY+2008,                    Ne
  Uchida+, in prep.                      Ozawa+2009
     SN1006: Searching for Fe emission
- Prototypical Type Ia SNR, but emission from Fe has never been detected.

                           BeppoSAX MECS         - Only one possible detection
                                  spectrum         reported by BeppoSAX
                                     Fe?         - XMM-Newton failed to detect

Chandra image
                       Vink+00



                                  Detected! but weak despite of its Type Ia origin
                                     Fe-K centroid ~ 6420eV (< Ne-like)
                                     … Corresponding net is ~ 1 x 109 cm-3 s

                                                Fe16+               Fe24+
  Suzaku spectrum                                                       Fe25+
  (HY+08)
                                                                            Fe26+
SN1006: Multiple net Components in Si
         broad feature

    Mg
                      Si
                               S


      C~O-like   He-like



                                      Reverse shock heats from outer region
                                          Outer ejecta = highly ionized
                                          Inner ejecta = lowly ionized

  Si6+ Si8+
                                       Approx with 2-net components
              Si12+
                       Si13+
                                       for Si and S ejecta
                                            net1 ~ 1×1010 cm-3 s
                                            net2 ~ 1×109 cm-3 s
                                              cf. Fe: net ~ 1×109 cm-3 s
              Si ion fraction @1keV
SN1006: Fullband Spectrum & Abundances
                                       Derived abundance ratios compared
                                       to the W7 model of Nomoto+84

                               Fe        Outer ejecta


   HY+08


                                         Inner ejecta



  ISM (w/ solar abundance)
  Outer ejecta (net ~ 1010 cm-3 s)
  Inner ejecta (net ~ 109)
  Non-thermal (synchrotron)

     Suggests stratified composition with Fe toward the SNR center,
     which results in the lowly-ionized (thus weak) Fe emission
Ejecta Stratification in Type Ia SN/SNRs
XMM image of Tycho




                                                        SN 2003du
 Decourchelle+01
                                                        (Tanaka+10)
   Color: Si-K
   Contour: Fe-K
                        Enclosed mass
 Radial
 profile                                       IME
                                                     Mazzali+07

                                        56Ni
            Si
           Fe                                           See also
                                                        Badenes+06
      Radius (arcmin)
SN1006 (Type Ia SNR)    W49B (CC SNR)




                                         S   S Ar        Fe
                                                    Ca
                                         i
                       Artificial
                        features
                       (a sort of bgd)
                                                          Ni

                                    Mg

  HY+2008,                    Ne
  Uchida+, in prep.                      Ozawa+2009
        W49B: Peculiar Ionization State
                 He-like Fe Ka            Ejecta is highly ionized to be He-like
     Cr
          Mn      Ni + Fe Kb              Radiative recombination continuum
                                              Fe25+ + e- → Fe24+ + hn
                            Fe-K RRC      … indicates presence of a large fraction
                                              of H-like Fe
               H-like Fe
                                           Measured kTe ~ 1.5 keV
                            Ozawa+09
                                             Fe ion population in a CIE plasma

                                                 Fe16+        Fe24+           Fe26+
                                                                      Fe25+
- RRC can be enhanced only when
  the plasma is recombining
  (e.g., photo-ionized plasma)

Similar recombining SNRs                             Temperature (keV)
 - IC443 (HY+09)
 - SNR 0506-68 (Broersen+11)           “Recombining NEI” in SNRs is not unique
 - other 3 & a few candidates           => Need to define “recombination age”
              W49B: Possible Progenitor
Explosion in dense CSM
                                                       Shimizu+12
- Numerical (Shimizu+12)
- Analytical, more progenitor-                          blast wave
  oriented (Moriya 12)
                                                                     reverse shock
 Blast wave breakout into ISM
  BW speed becomes faster and expand                          2nd reverse shock
   adiabatically, resulting in rapid cooling
   with “frozen” ionization state




                                                            Type II-P or IIn
                                                            could be a progenitor
                                                            of a recombining SNR
                                                            (Moriya 12)

RSG case (vw ~ 10 km/s)          WR case (vw ~ 1000 km/s)
                        Fe-K diagnostics
Extreme cases have been shown
    SN1006: Type Ia SNR, Fe lowly-ionized due to a low ambient density and
            ejecta stratification with Fe more concentrated toward the center
    W49B: CC SNR, Fe over-ionized (recombining),
            possibly due to interaction with high-density CSM
            … and inhomogeneous ejecta structure?




                                                 Red: Si
                                                 Blue: Fe
                                                 Green: continuum



                                                           Other SNRs?
                       Fe-K diagnostics
                                      - Type Ia and CC SNRs are clearly
       Type Ia                          separated (CC more ionized)
                                      - Luminosity of both groups are
                                        distributed in the similar range.


                             CC

                                      Can be explained by ionization
                                      (and temperture, density effects)
     (HY+, in prep.)                   --- Measuring ionization state is
                                           essential for measuring
                                           element abundances!!




net = 5x109       1x1010     5x1010         1x1011            3x1011
                           Fe-K diagnostics
                                                       Ionization ages expected if the SNRs
                                                        have evolved in uniform ISM with
             Type Ia                                    typical density




                                          CC



                                                                                Hachisu+01
        (HY+, in prep.)




If the SD scenario is the case, a large, low-density
 cavity is expected around the progenitor

No evidence of an “accretion wind” and a                                    Badenes+07
resultant cavity but for a few Type Ia SNRs
Evidence of cavity/CSM in Ia SNRs




                                      Kepler (Reynolds+07)




      RCW86 (Williams+11)
Unique Ia SNR where the presence of
a surrounding cavity is suggested

                                       N103B (Lewis+03)
                          Summary
- X-ray observation of SNRs is one of the best methods to study
  stellar/explosive nucleosynthesis. (optically-thin, K-shell emission)
- Understanding of non-equilibrium in ionization is, however,
  essential for accurate measurement of element abundances.
- Fe emission in Type Ia SNRs is commonly weak due to low-density
  ambient and stratified chemical composition.
- In CC SNRs, on the other hand, Fe is highly ionized, sometime
  overionized, possibly due to initial CSM interaction.
- No evidence of a large cavity expected from an “accretion wind”
  around Type Ia SNRs, except for RCW86, constraining progenitor
  system??

				
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posted:8/1/2013
language:English
pages:21