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Discovery of K a lines of neutral sulfur, argon, and calcium atoms from the Galactic Center

Discovery of K a lines of neutral sulfur, argon, and calcium atoms from the Galactic Center. Masayoshi Nobukawa, Katsuji Koyama, Takeshi Go Tsuru, Syukyo G Ryu (Kyoto Univ.). Neutral Fe line from the Galactic center Discovery of neutral K a lines of S, Ar, Ca, Cr, Mn

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Discovery of K a lines of neutral sulfur, argon, and calcium atoms from the Galactic Center

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  1. Discovery of Ka lines of neutral sulfur, argon, and calcium atoms from the Galactic Center Masayoshi Nobukawa, Katsuji Koyama, Takeshi Go Tsuru, Syukyo G Ryu (Kyoto Univ.) • Neutral Fe line from the Galactic center • Discovery of neutral Ka linesof S, Ar, Ca, Cr, Mn • What is the origin of the neutral lines ? • Summary

  2. Neutral Fe line emission from the GC 6.4 keV (neutral Fe-Ka) line shows a clumpy distribution in the Galactic center. Neutral clumps are correlated with giant molecular clouds (Sgr B2, Radio Arc regions…) Bright source 1E 1743.1-2843 6.4keV map Sgr A East (SNR) Sgr B2 Sgr B1 M0.74-0.09 Sgr B2 20’ (50 pc) Radio Arc G0.174-0.233 Sgr B2 Radio Arc Sgr B2 Neutral iron line Molecular gas CS (J=1-0) Spectrumof Sgr B2 ・prominent neutral Fe line ・strongly absorbed continuum (NH~1024 cm-2) 3 4 5 6 7 8 Energy (keV)

  3. Other neutral lines ? Lighter elements, S, Ar, Ca, Cr, Mn are expected to exist in the molecular cloud. S Fe=1 Ar Ca Ni Cr Mn *solar abundance Let’s search for the neutral lines from the lighter elements !! 3/11 Low energy K-Shell lines are absorbed by ISM.

  4. The strongest neutral clump Neutral Fe S Si Ar Fe Ca He, H-like lines; mainly due to plasma Other neutral lines are weak. (Ratio to Fe is < 0.01—0.1) => The brightest neutral clump in the GC 6.4keV map Sgr A East (SNR) Sgr B2 Sgr B1 M0.74-0.09 selected region Sgr B2 20 arcmin Radio Arc G0.174-0.233 Blue: neutral Red: plasma components

  5. Spectral fitting of the 6.4 keV clump X-ray emission from the GC: (Koyama+07, Ryu+09) kT~ 1 keV plasma (He, H-like Si, S, Ar, Ca) kT~ 7 keV plasma (He-, H-like Fe, Ni) neutral clump (lines + continuum) Fitting model: 2 temp. plasmas (kT~1 keV + 7 KeV) neutral component (lines + continuum) Abs (ISM) Abs (MC) x x Add He-like Cr, Mn lines (APEC does not contain) Firstly, neutral lines; only Fe Ka, Kb + Ni Ka

  6. NH(ISM) =7.1(±0.3)x1022cm-2 (Typical for the GC) S Ar Ca Cr Mn kT1 = 0.99 ± 0.02 keV kT2 = 7.02 ± 0.33 keV Z(Si) = 1.3 ± 0.1 solar Z(S,Ar,Ca) = 1.6 ± 0.1 Z(Fe/Ni) = 1.2/2.1(fixed) (Koyama+07) He-like Cr, Mn lines are firstly detected !! These residuals correspond to neutral S, Ar, Ca, Cr, Mn. neutral lines: Fe-Ka, Kb, Ni-Ka continuum: NH(MC) = 1.7 ± 0.3 x1023 cm-2 G = 1.85 ± 0.15 (90% errors)

  7. Blue: neutral Red: plasma Fe Mn S Ar Cr Ca Ni without S, Ar, Ca, Cr, Mn lines c2 = 355/208 c2 = 243/203 with S, Ar, Ca, Cr, Mn lines 7/11

  8. Discovery of neutral S, Ar, Ca, Cr, Mn lines Observed line intensity graph 90% errors Observed Line intensity S Ar Ca Cr Mn Fe Ni Newly detected !! 8/11

  9. What is the origin of the neutral lines ? Line emission Line: Ionization of neutral atoms by injected X-rays / electrons. Continuum: Thomson scattering (X-ray) Bremsstrahlung (electron) Injection of X-ray / electron molecular cloud NH = 1023 cm-2 Continuum Calculation of EWs by Geant4 Assumptions: uniform density of the MC solar abundance index of 2 (X-ray) / 3 (electron) <= observed spectral index of ~2 Mn Fe Fe S Ca Cr Ar Different processes would make different spectra. => Equivalent width (EW) is a good indicator for the origin. 9/11

  10. Equivalent width and the origin X-ray origin Preliminary EWs of S—Ni would prefer the X-ray origin electron origin 90% errors S Ar Ca Cr Mn Fe Ni Models are calculated by Geant4 Assumed solar abundance

  11. Summary We successfully detected fluorescence K-shell lines from S, Ar, Ca, Cr, Mn from the brightest neutral clump of the Galactic center. Equivalent Widths of the neutral lines would suggest X-ray origin rather than electron one. Thank you

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