2002ApJ...575..855Q -
Astrophys. J., 575, 855-859 (2002/August-3)
A thermal bremsstrahlung model for the quiescent X-ray emission from Sagittarius A*.
QUATAERT E.
Abstract (from CDS):
I consider the thermal bremsstrahlung emission from hot accretion flows (Bondi/ADAFs), taking into account the finite size of the observing telescope's beam (Rbeam) relative to the Bondi accretion radius (RA). For Rbeam≫RA, soft X-ray emission from the hot interstellar medium surrounding the black hole dominates the observed emission, while for Rbeam≪RA, hard X-ray emission from the accretion flow dominates. I apply these models to Chandra observations of the Galactic center, for which Rbeam~RA. I argue that bremsstrahlung emission accounts for most of the ``quiescent'' (nonflaring) flux observed by Chandra from Sgr A*; this emission is spatially extended on scales ∼RA∼1" and has a relatively soft spectrum, as is observed. If accretion onto the central black hole proceeds via a Bondi or ADAF flow, a hard X-ray power law should be present in deeper observations with a flux ~(1)/(3) of the soft X-ray flux; nondetection of this hard X-ray component would argue against ADAF/Bondi models. I briefly discuss the application of these results to other low-luminosity active galactic nuclei.
Abstract Copyright:
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Journal keyword(s):
Accretion, Accretion Disks - Galaxy: Center
Simbad objects:
9
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