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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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