Transcript Chandraでみた超新星残骸 G0.57

Discovery of New SNR Candidates
in the Galactic Center Region with ASCA and Chandra
Atsushi
1
1
Senda ,
2
Murakami ,
Hiroshi
Aya
1
Bamba ,
1
Takagi ,
Shin-ichiro
and Katsuji
1
Koyama
Department of Physics, Kyoto University, Japan; 2 Institute of Space and Astronautical Science (ISAS), Japan
E-mail: [email protected]
1. Introduction
What is the origin of the diffuse X-ray emission near the GC?
･Multiple Supernovae (～1000 SNe / 105 yr) ?
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.
･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).
･ electron temperature kT ～ 10 keV
･ total thermal energy E ～ 1054 ergs
･ an age of the plasma t ～ 105 year
In this paper, we investigate newly discovered clumpy structures near the GC to reveal the origin
of the diffuse X-ray emission.
2. Observations and X-ray Images
Chandra Observation log
Obs Name
Coordinates
Exporsure
l [deg] b [deg] [ksec]
359.94 -0.05
48.7
0.59
-0.02
99.0
0.00
-0.20
11.8
0.00
0.00
10.8
359.80
-0.20
11.8
359.80
0.00
10.8
359.61
-0.20
10.8
359.61
0.00
10.8
Sgr A*
Sgr B2
GCS13
GCS14
GCS16
GCS17
GCS19
GCS20
0.7°
0.6°
0.2°
l = 0.0°
359.8°
359.6°
0.2°
b = 0.0°
l = 0.0°
359.8°
359.6°
b = 0.0°
G359.77-0.09
0.5°
0.1°
G359.92-0.09
G0.570-0.018
0.0°
-0.2°
-0.2°
G359.79-0.26
-0.1°
ACIS Sgr B2 region 6.0-7.0 keV
Chandra ACIS Galactic Center 3.0-8.0 keV
Chandra ACIS Galactic Center 1.0-3.0 keV
3. Individual diffuse sources
G0.570-0.018
G359.79-0.26 and G359.77-0.09
G359.92-0.09
G0.570-0.018 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.
Ho et al. (1985) reported that there is nonthermal 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.
15“～0.6 pc
Best fit results of the thermal NEI model
G0.570-0.018
6.1 (3.1—26)
1.7 (1.3—2.7)
13.9 (10.7—17.2)
4.5 (>1.6)
8.2 (7.7—8.7)
41.2/40
kT [keV]
τ [1010 s-1 cm-3]
NH [1022 H cm-2]
Abundance [solar]
Flux [ergs s-1 cm-2]
χ2/d.o.f.
58’
Sgr A East
-29°00’
G359.92-0.09
02’
wisp
04’
ACIS 3.0-8.0 keV
40s
kT
(3.4<)
[keV]
τ
wisp
VLA 6cm (Ho et al. 1985)
NH
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 (～
1051 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.
H
6.0
cm-2]
Flux
[10-12 ergs s-1 cm-2]
χ2/d.o.f.
(3.7—8.3)
1.5
(0.01 <)
18
(7.0—33)
0.4
44.3/38
Best fit results of the thermal VNEI model
kT
[keV]
τ
[1011 s cm-3]
NH
[1022 H cm-2]
Flux
[10-12 ergs s-1 cm-2]
Abundances[solar]
Si
S
Ar
Ca
χ2/d.o.f.
EH
(7.1—80.0)
2.1
(0.8—5.4)
20s
G359.92-0.09
wisp
12.5
(1.9 <)
1.4
[1011 s cm-3]
[1022
SW
2.6
17h42m30s
R.A. (1950)
Sgr A East
Best fit results of the thermal NEI model
EH
11.4
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.
9.8/9
190
(0.001 <)
35
SE
(29—40)
0.4
8.83/7
・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)
･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 ?
5. Summary
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.
(b)
(c)
G0.570-0.018
G359.79-0.26
G11.2-0.3
=
+
(a)
(d)
AX J1841.0-0536
G25.5+0.0
GC plasma
G28.6-0.1
G11.0+0.0
G26.6-0.1
Γ=1.6
(b)
Black :
Chandra ACIS
Green, Red : ASCA GIS 2, GIS3
Blue :
ROSAT PSPC
Supposed two clumps are the part of a large shell-like structure,
its energetics are consistent with that of a typical SNR.
non-thermal sources
(a)
0.4 (0.3—0.6)
0.8 (0.5—1.0)
1.3 (0.4—2.2)
3.4 (1.4—5.6)
197.6/163
G359.79-0.26
By applying Sedov self-similar model
R = 16.5 pc
E = 2.1 x 1051 ergs
kT = 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)
(Senda et al. 2002, ApJ)
The origin of the thermal diffuse emission for the GC region
0.6 (0.4—0.9)
0.8 (0.5—2.1)
0.3 (< 1.0)
1.4 (< 3.3)
153.9/109
G359.79-0.26
0.82
(0.75—0.93)
64
(5.6 <)
4.9
(4.6—5.2)
2.3
wisp
Young (3800—12000 yr) SNR
4. Discussion
G359.77-0.09
1.31
(1.03—1.79)
0.5
(0.1—1.6)
5.8
(5.1— 6.5)
2.2
G359.77-0.09
Γ=1.8
(c)
Γ=1.3
(d)
Γ=2.1
•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 G359.920.09), 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.
References
Images: ASCA GIS 0.7-10keV (coordinates are in Galactic)
Spectra: GIS2+3 data fitted with power-law model
Bamba, A. et al. 2001, PASJ, 53, L21
Bamba, A. et al. 2002, submitted to ApJ
Coil, A. L, and Ho, P. T. P. 2000, ApJ, 533, 245
Koyama, K. et al. 1989, nature, 339, 603
Koyama, K. et al. 1996, PASJ, 48, 249
Ho, P. T. P. et al. 1985, ApJ, 288, 575
Maeda, Y. et al. 2002, ApJ, 570, 671
Murakami, H. 2002, Ph.D thesis, Kyoto Univ.
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Senda, A et al. 2002, ApJ, 565, 1017
Ueno, M. et al. 2002, submitted to ApJ
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