Discovery of New SNR Candidates Discovery of New SNR Candidates in the Galactic Center Region with ASCA and Chandrain the Galactic Center Region with ASCA and Chandra

Atsushi SendaAtsushi Senda11, Hiroshi Murakami, Hiroshi Murakami22, Aya Bamba, Aya Bamba11, Shin-ichiro Takagi, Shin-ichiro Takagi11, and Katsuji Koyama, and Katsuji Koyama11

1 1 Department of Physics, Kyoto University, Japan; Department of Physics, Kyoto University, Japan; 2 2 Institute of Space and Astronautical Science (ISAS),Institute of Space and Astronautical Science (ISAS), JapanJapanE-mail: E-mail: senda@cr.scphys.kyoto-u.ac.jpsenda@cr.scphys.kyoto-u.ac.jp

1. Introduction1. Introduction The origin of the diffuse X-ray emission from the Galactic Center (GC) region has been an open issue over decades. Ginga and ASCA found the large-scale ( ～ 1°x 1°) thin-thermal plasma with strong lines from ionized iron (Koyama et al. 1989; 1996, Yamauchi et al. 1990). The physical properties of the large scale hot plasma are as below.

　 　･ electron temperature kT ～ 10 keV 　　 ･ total thermal energy E ～ 1054 ergs　　 ･ an age of the plasma 　 t ～ 105 year

Black : Chandra ACISGreen, Red : ASCA GIS 2, GIS3Blue : ROSAT PSPC

G359.79-0.26

G359.77-0.09

G0.570-0.018G0.570-0.018 G359.92-0.09G359.92-0.09 G359.79-0.26 and G359.77-0.09G359.79-0.26 and G359.77-0.09G0.570-0.018 is discovered by ASCA (Sakano et al. 2002). Chandra observation resolved this source as extended, shell-like structure. Obtained X-ray spectrum is consistent with that obtained with ASCA, which exhibits extremely strong Fe-K line emission .The combined X-ray spectra are well reproduced by a thermal NEI model.

The narrow band image of the Chandra GC Survey shows that soft diffuse emissions extend from the Galactic Center to the galactic southeast direction. The extended emission is relatively soft and clumpy distributed. From these clumps, we focused on the two bright clumps and named G359.79-0.26 and G359.77-0.09. These clumps were also detected with ASCA and ROSAT.X-ray spectra of each clumps exhibit K-line emissions from He-like and H-like ions such as Si, S, Ar, and Ca. The results of the spectral fitting with thermal NEI model show that their physical parameters (NH and metal abundances) are similar to each other. In addition, the 1-3 keV band image shows G359.79-0.26 and G359.77-0.09 are south and north part of the large ( ～ 30 pc) elliptical shell, respectively.These indicate that the two clumps have the same origin, an energetic explosion such as a supernova occurred at the center of the large shell.

　　　 G359.77-0.09 G359.79-0.26 kT 　　 1.31 0.82 [keV] (1.03—1.79) (0.75—0.93) τ 0.5 64[1011 s cm-3] (0.1—1.6) (5.6 <) NH 5.8 4.9[1022 H cm-2] (5.1— 6.5) (4.6—5.2) Flux 2.2 2.3[10-12 ergs s-1 cm-2]Abundances[solar] Si 0.6 (0.4—0.9) 0.4 (0.3—0.6) S 0.8 (0.5—2.1) 0.8 (0.5—1.0) Ar 0.3 (< 1.0) 1.3 (0.4—2.2) Ca 1.4 (< 3.3) 3.4 (1.4—5.6) χ2/d.o.f. 153.9/109 197.6/163

Best fit results of the thermal VNEI model

G359.79-0.26

G359.77-0.09b = 0.0°

0.2°

-0.2°

l = 0.0° 359.8° 359.6°

15“ ～ 0.6 pc

G0.570-0.018 kT 　 [keV] 6.1 (3.1—26) τ [1010 s-1 cm-3] 1.7 (1.3—2.7) NH [1022 H cm-2] 13.9 (10.7—17.2) Abundance [solar] 4.5 (>1.6) Flux [ergs s-1 cm-2] 8.2 (7.7—8.7) χ2/d.o.f. 41.2/40

Best fit results of the thermal NEI model

VLA 6cm (Ho et al.

1985)

G359.92-0.09

wisp

Sgr A East

EH

wisp

SE

EH SW wisp kT 　 11.4 2.6 12.5 [keV] (3.4<) (1.9 <) (7.1—80.0) τ 1.4 2.1 190[1011 s cm-3] (0.8—5.4) (0.01 <) (0.001 <) NH 6.0 18 35[1022 H cm-2] (3.7—8.3) (7.0—33) (29—40) Flux 1.5 0.4 0.4[10-12 ergs s-1 cm-2] χ2/d.o.f. 44.3/38 9.8/9 8.83/7

Best fit results of the thermal NEI model

・ E. M. = 1.1 x 1057 cm-3

・ EEH = 1.6 x 1050 ergs・ ne = 0.4 cm-3

・ t = 3800 yr (from the sound velocity@10keV)

1.2 x 104 yr (from an ionization parameter)

By applying Sedov self-similar model R = 0.4 pc E = 3.5 x 1048 ergs kT = 6.1 keV na = 5.1 cm-3 E.M.= 8.1 x 1056 cm-3 t = 70 yrs

⇒The swept up mass (M= na x 4/3πR3 = 0.03Mo) and estimated initial energy are both extremely small compared with that of a usual SNR. ⇒ Only a tiny fraction of the explosion energy ( ～ 105

1 ergs) and ejected mass ( ～ a few Mo) are converted to thermal plasma.G0.570-0.018 is a young SNR which is not in an adiabatic phase but still in a free expansion phase.(Senda et al. 2002, ApJ)

non-thermal sourcesnon-thermal sources4. Discussion4. Discussion

･ GC plasma has at least two temperature thermal components　 kT ～ 10keV hard component ← G359.92-0.09, G0.570-0.018 kT ～ 1 keV soft component 　 ← G359.77-0.09 and G359.79-0.26 ･ To explain the total luminosity of GC diffuse emission ( ～ 2 x 1038 ergs/s) with the sum of SNRs, ～ 100 SNRs should be detected in an X-ray band, which are far grater than the number of the present detection. ⇒ 　 Undetected SNRs ? 　 Other origin ?

=

G359.79-0.26

+GC plasma

G11.0+0.0G11.2-0.3

(a)

G25.5+0.0

(b)

G26.6-0.1

AX J1841.0-0536(c)

G28.6-0.1

(d)

(a)

(b) (c) (d)

In the Galactic plane, a number of Synchrotron X-ray dominant SNRs (SXSs) have been found with ASCA (Bamba et al. 2001, 2002) and Chandra (Ueno et al. 2002). In the GC region, no SXSs have ever been found, however, deep observations with Chandra or Newton will be found SXSs in the GC region.

The origin of the thermal diffuse emission for the GC regionThe origin of the thermal diffuse emission for the GC region

ACIS Sgr B2 region 6.0-7.0 keV

G0.570-0.018

Obs Name Coordinates Exporsure l [deg] b [deg] [ksec]

Sgr A* 359.94 -0.05 48.7Sgr B2 0.59 -0.02 99.0GCS13 0.00 -0.20 11.8GCS14 0.00 0.00 10.8GCS16 359.80 -0.20 11.8GCS17 359.80 0.00 10.8GCS19 359.61 -0.20 10.8GCS20 359.61 0.00 10.8

Chandra Observation log

2. Observations and X-ray Images2. Observations and X-ray Images

Chandra ACIS Galactic Center 3.0-8.0 keV

b = 0.0°

-0.2°

l = 0.0° 359.8° 359.6°

G359.92-0.09

0.2°

What is the origin of the diffuse X-ray emission near the GC? What is the origin of the diffuse X-ray emission near the GC? 　　　･Multiple Supernovae ( ～ 1000 SNe / 105 yr) 　 ?

　　　･ Energetic explosion of the massive black hole Sgr A* ?

Recent results of Chandra confirmed that the most of X-ray flux (both continuum and Fe-K line emission) from the GC region is truly diffuse (Wang et al. 2002). On the other hand, surface brightness of the diffuse emission is found to be rather clumpy. The presence of the clumpy structures may favor the multiple-SNe scenario. In fact, new X-ray SNRs have been discovered by observations with Chandra (e.g. Maeda et al. 2002).

In this paper, we investigate newly discovered clumpy structures near the GC to reveal the origin of the diffuse X-ray emission.

3. Individual diffuse sources 3. Individual diffuse sources

5. Summary5. Summary

0.0°

-0.1°

0.1°

0.7° 0.6° 0.5°

Ho et al. (1985) reported that there is non-thermal radio shell located about 5’ south of the SNR Sgr A East, and named it G359.92-0.09 as a possible GC SNR candidate. Chandra observation reveals an X-ray excess fills an eastern half (EH) and southwest(SW) part of the radio shell G359.92-0.09. Northwest part shows no excess in the shell because of the contamination of the intense X-ray emission from Sgr A East.In the southwest edge of the shell, an X-ray bright filament are also discovered, which clearly corresponds with a non-thermal radio filament called “wisp”. X-ray spectra are extracted from three different region; Eastern half (EH), Southwest quadrant (SW), and wisp.An thermal NEI model yields an acceptable fit for a spectrum from each region.

wisp

G359.92-0.09

Sgr A East58’

02’

-29°00’

04’

20s17h42m30s40s

ACIS 3.0-8.0 keV

Dec

(19

50

)

R.A. (1950)

•With Chandra data, we found diffuse emission from the GC region has clumpy structures. •Some of these clumps show thermal spectra from high temperature ( ～ 10keV) plasma (G0.570-0.018 and G359.92-0.09), some show that from lower temperature ( ～ 1keV) plasma (G359.77-0.09 and G359.79-0.26). •Their shell-like morphology and energetics suggest that they are SNRs. G359.92-0.09 has a counterpart of a non-thermal radio shell.• Total diffuse emission from the GC emission is grater than that of GC SNRs by 1—2 order of magnitude, hence a relation between the GC diffuse and SNRs is unclear yet. • Recently, a number of SXSs are found in the Galactic Plane, while no SXS has found yet in the GC region.

Images: ASCA GIS 0.7-10keV (coordinates are in Galactic)Spectra: GIS2+3 data fitted with power-law model

G0.570-0.018

Γ=1.6 Γ=1.8 Γ=1.3 Γ=2.1

Chandra ACIS Galactic Center 1.0-3.0 keV

By applying Sedov self-similar modelR = 16.5 pc E = 2.1 x 1051 ergskT = 0.8 keV na = 0.3 cm-3

E. M. = 1.47 x 1059 cm-3 t = 6900 yr t = 2.4x104 yr (from an ionization parameter)

Supposed two clumps are the part of a large shell-like structure,its energetics are consistent with that of a typical SNR.

Young (3800—12000 yr) SNR

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