Thermal X‐Ray Iron Line Emission from the Galactic Center Black Hole Sagittarius A*

Abstract

We model thermal X-ray emission from the accreting supermassive black hole Sagittarius A Ã at the Galactic center. For the region inside 1B5 of the center, we use a generalized radiatively inefficient accretion flow ( RIAF) model, and for the region out to 10 00 we use published models of the ambient hot gas. We calculate the equivalent widths of hydrogen-like and helium-like emission lines of various elements, notably iron. We predict that a strong helium-like iron line with an equivalent width $1 keV should be emitted by both the external medium and the RIAF. The equivalent width in the external medium is sensitive to the metallicity Z of the gas as well as the mean temperature. For reasonable choices of these parameters, the calculated results agree with Chandra's detection of an iron line with an equivalent width of 1.3 keV within 10 00 . The emission from within 1B5 is not sensitive to the external temperature, but is sensitive to the density and, especially, temperature profile inside the Bondi radius. For the range of profiles we consider, we calculate the equivalent width of the iron line to be $0.6-1.5(Z/Z ) keV, where Z is the solar metallicity. We present a new Chandra spectrum of the quiescent emission within 1B5 of Sgr A Ã . The measured equivalent width of the iron line is 0.7 keV. Although this measurement has a large uncertainty, it is consistent with our predictions, provided the metallicity of the gas is approximately solar.

Star Formation in Low Radio Luminosity Active Galactic Nuclei from the Sloan Digital Sky Survey

“…Locally, accurate black hole mass measurements have been made for our own Galaxy (e.g., Schödel et al 2003;Ghez et al 2005) and the Andromeda galaxy (e.g., Bender et al 2005). Our own Galactic black hole is rather dormant based on its relatively low X-ray emission (e.g., Baganoff et al 2003;Xu et al 2006), but in general these massive black holes are considered a key component of active galactic nuclei (AGNs), in which accretion onto the black hole itself can produce large amounts of energy efficiently (e.g., Lynden-Bell 1969;Pringle 1981).…”

A powerful flare from Sgr A* confirms the synchrotron nature of the X-ray emission

“…Sgr A ⋆ also appears as a faint (L 2−10 keV ∼ 2×10 33 erg s −1 ) X-ray source (Baganoff et al 2003;Xu et al 2006) observed to be extended with a size of about ∼ 1 ′′ . The observed size is comparable to the Bondi radius and the quiescent X-ray emission is thought to be the consequence of material that is captured at a rate of 10 −6 M⊙ yr −1 from the wind of nearby stars (Melia 1992;Quataert 2002;Cuadra et al 2005;.…”

Chandra Observations of the Galactic Center: High Energy Processes at Arcsecond Resolution

“…Interestingly, the observed spectrum of the emission resembles that of the surrounding diffuse plasma and shows the Fe Kα line at ∼ 6.6 keV ( Fig. 10d; Wang et al 2006b;Xu et al 2006). Therefore, the flow is also in an NEI state.…”