Discovery of K 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 lines of S, Ar, Ca, Cr, Mn• What is the origin of the neutral lines ?• Summary 1/11

Neutral Fe line emission from the GC

2/11

Molecular gas CS (J=1-0)

6.4 keV (neutral Fe-K) line shows a clumpy distribution in the Galactic center.

Neutral clumps are correlated with giant molecular clouds (Sgr B2, Radio Arc regions…)

Spectrum of Sgr B2　　・ prominent neutral Fe line　　・ strongly absorbed continuum (NH~1024 cm-2)3 4 5 6 7 8

Energy (keV)

Sgr B2

Neutral iron line

Sgr B2 Radio Arc

6.4 keV map

Sgr B2

Sgr B1

M0.74-0.09

G0.174-0.233

Sgr A East (SNR)

Bright source1E 1743.1-2843

20’ (50 pc)

Sgr B2Radio Arc

Fe=1

Ni

Mn

S

ArCa

Cr

*solar abundance

Other neutral lines ?

Lighter elements, S, Ar, Ca, Cr, Mn are expected to exist in the molecular cloud.

Let’s search for the neutral lines from the lighter elements !!Low energy K-Shell lines

are absorbed by ISM. 3/11

The strongest neutral clump

4/11

Other neutral lines are weak. (Ratio to Fe is < 0.01—0.1)=> The brightest neutral clump in the GC

Sgr B2 Radio Arc

6.4 keV map

Sgr B2

Sgr B1

M0.74-0.09

G0.174-0.233

Sgr A East (SNR)

selectedregion20 arcmin

Neutral Fe

He, H-like lines;mainly due to plasma

Si S Ar

Ca

Fe

Blue: neutralRed: plasma components

Spectral fitting of the 6.4 keV clump

5/11

Fitting model:

2 temp. plasmas (kT~1 keV + 7 KeV)

neutral component(lines + continuum)

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)

Firstly, neutral lines; only Fe K, K + Ni K

Abs(MC)

Abs(ISM)

x x

Add He-like Cr, Mn lines(APEC does not contain)

kT1 = 0.99 ± 0.02 keVkT2 = 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 !!neutral lines: Fe-K, K, Ni-Kcontinuum: NH(MC) = 1.7 ± 0.3 x1023 cm-2

= 1.85 ± 0.15

NH(ISM) =7.1(±0.3)x1022cm-2 (Typical for the GC) S Ar Ca Cr Mn

These residuals correspond to neutral S, Ar, Ca, Cr, Mn.

(90% errors)

S ArCa Cr

Mn

Fe

Ni

without S, Ar, Ca, Cr, Mn lines

with S, Ar,Ca, Cr, Mnlines 7/11

2 = 243/203

2 = 355/208

Blue: neutralRed: plasma

Element S Ar Ca Cr Mn Fe Ni

Significance　()

3.5 3.2 8.1 4.5 4.6 85 5.7

Newly detected !!

Observed line intensity graph

Discovery of neutral S, Ar, Ca, Cr, Mn lines

S Ar Ca Cr Mn Fe Ni

90% errors

8/11

Obs

erve

d Li

ne in

tens

ity

What is the origin of the neutral lines ?

molecular cloudNH = 1023 cm-2

Line emission

Injection ofX-ray / electron

Line: Ionization of neutral atoms by injected X-rays / electrons.Continuum: Thomson scattering (X-ray) Bremsstrahlung (electron)

Fe

Fe

Ar

S

CaCr

Mn

9/11

Continuum

Different processes would make different spectra.=> Equivalent width (EW) is a good indicator for the origin.

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

10/11

S Ar Ca Cr Mn Fe Ni

Equivalent width and the origin

X-ray origin

electron origin

EWs of S—Ni would prefer the X-ray origin

Preliminary

Models are calculated by Geant4Assumed solar abundance

90% errors

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

11/11