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Most of the 6.4 keV clumps show strong Ka line with the equivalent width of 1.1 – 2.1 keV, and deep K-edge absorption with 2 – 10 x 1023 cm-2 (>> 1 x 1023 :the interstellar absorption to the GC)X-rays is more likely than Electrons.
Inner Shell Ionization Electrons vs X -rays---------------------------------------------Equivalent witdh (keV) of the 6.4 keV line 0.3 - 0.6 1 - 1.5 Energy (keV) of the Max Cross Section 10-100 7.1 Absorption NH (cm-2) ~1021 ~1024
Origin of the 6.4 keV clumpsInner shell Ionization by Electrons or X-rays ?
6.4 keV lineHistory ofSgr B2 from 1994 to 2005
~10pc
M 0.66 G 0.570
Direct evidence: time variability from the Sgr B2
6.4 keV6.4 keV
6.7keV6.7 keV
6.7 keV Full Region
6.4 keV G0.57
6.4 keV M0.66
1.4 -
1.2-
1.0-
0.8-
3.5 -
3.0-
2.5-
2.0-
1.5-
1.0-
0.5-
Physical size of the clump complex is nearly 10 pc. Therefore, such a large flux change within 10 years is impossible by any charged particle.
Only possible scenario of this time variability is due to an irradiation of variable X-rays (X-ray Reflection Nebula).
More than a few hundred years ago, Sgr A* had been very active in X-rays; 106 times brighter thannow at ~300 years ago, decayed to less than a half after ~10 years. The X-rays hit the Sgr B clouds after ~300-years travel. The clouds re-emitted the 6.4 keV photons. Like a time delayed-echo, the X-ray echo is now just arriving at the Earth, when Sgr A* is falling into a quiescent state.