Iron and Nickel Line Diagnostics for the Galactic Center Diffuse Emission

Abstract

We have observed the diffuse X-ray emission from the Galactic center (GC) using the X-ray Imaging Spectrometer (XIS) on Suzaku. The high-energy resolution and the low-background orbit provide excellent spectra of the GC diffuse X-rays (GCDX). The XIS found many emission lines in the GCDX near the energy of K-shell transitions of iron and nickel. The most pronounced features are Fe I Kα at 6.4 keV and K-shell absorption edge at 7.1 keV, which are from neutral and/or low ionization states of iron, and the K-shell lines at 6.7 keV and 6.9 keV from He-like (Fe XXV Kα) and hydrogenic (Fe XXVI Lyα) ions of iron. In addition, Kα lines from neutral or low ionization nickel (Ni I Kα) and He-like nickel (Ni XXVII Kα), and

Origin of thermal and non-thermal hard X-ray emission from the Galactic center.

“…SUZAKU observations [13] found also clear evidence for a hot plasma in the galactic central region with the diameter about 20 acrminutes (i.e ∼ 50 − 60 pc). Using the 6.9/6.7 keV ratio it was concluded that the spectrum in 5-11.5 keV range was naturally explained by a 6.5 keV-temperature plasma in collisional ionization equilibrium.…”

“…Therefore, the origin of X-ray emission from there may be somewhat different from the rest of the Galaxy. Though observations shows there a significant contribution of discrete sources which apply from 20% to 40% of the total flux (see [11,12]), the SUZAKU data do not show correlation between the X-ray source distribution derived from Chandra data and the distribution of 6.7 keV line [13] that may contradict the source origin of hard X-ray emission from the Galactic center. Observations show also essential distinctions between X-ray emission from the Galactic ridge and from the Galactic center.…”

“…For the 1 • ÷ 2 • radius central region we take the temperature 6.5 keV and the density of this gas n ≃ 0.1 ÷ 0.4 cm −3 as it follows from observations [11,14,13].…”

Inflight performance and calibration of the NuSTAR CdZnTe pixel detectors

“…We compared the line energies that we obtain with NuSTAR to the results we obtained with Suzaku/XIS, which is an X-ray CCD camera with an accurate energy determination of ≲ 10 eV. 8 The observed spectra of NuSTAR and Suzaku/XIS in Figure 3 were individually fitted by a continuum model consisting of Energy (keV) Figure 3. Cas A spectra observed with (red) NuSTAR/FPMB and (black) Suzaku/XIS-3FI.…”

Restrictions on the injection energy of positrons annihilating near the Galactic center

“…This molecular gas occupies a rather small part of the central region, most of which is filled with a very hot gas. Recent SUZAKU measurements of the 6.9/6.7 keV iron line ratio [13] were naturally explained by a thermal emission of the 6.5 keV-temperature plasma. The plasma density was estimated in limits 0.1 − 0.2 cm −3 .…”