1,623 research outputs found
The X-ray flaring properties of Sgr A* during six years of monitoring with Swift
Starting in 2006, Swift has been targeting a region of ~21'X21' around
Sagittarius A* (Sgr A*) with the onboard X-ray telescope. The short,
quasi-daily observations offer an unique view of the long-term X-ray behavior
of the supermassive black hole. We report on the data obtained between 2006
February and 2011 October, which encompasses 715 observations with a total
accumulated exposure time of ~0.8 Ms. A total of six X-ray flares were detected
with Swift, which all had an average 2-10 keV luminosity of Lx (1-4)E35 erg/s
(assuming a distance of 8 kpc). This more than doubles the number of such
bright X-ray flares observed from Sgr A*. One of the Swift-detected flares may
have been softer than the other five, which would indicate that flares of
similar intensity can have different spectral properties. The Swift campaign
allows us to constrain the occurrence rate of bright (Lx > 1E35 erg/s) X-ray
flares to be ~0.1-0.2 per day, which is in line with previous estimates. This
analysis of the occurrence rate and properties of the X-ray flares seen with
Swift offers an important calibration point to asses whether the flaring
behavior of Sgr A* changes as a result of its interaction with the gas cloud
that is projected to make a close passage in 2013.Comment: 8 pages, 5 figures, 3 tables. Shortened, accepted to Ap
Relativistic X-ray Lines from the Inner Accretion Disks Around Black Holes
Relativistic X-ray emission lines from the inner accretion disk around black
holes are reviewed. Recent observations with the Chandra X-ray Observatory,
X-ray Multi-Mirror Mission-Newton, and Suzaku are revealing these lines to be
good probes of strong gravitational effects. A number of important
observational and theoretical developments are highlighted, including evidence
of black hole spin and effects such as gravitational light bending, the
detection of relativistic lines in stellar-mass black holes, and evidence of
orbital-timescale line flux variability. In addition, the robustness of the
relativistic disk lines against absorption, scattering, and continuum effects
is discussed. Finally, prospects for improved measures of black hole spin and
understanding the spin history of supermassive black holes in the context of
black hole-galaxy co-evolution are presented. The best data and most rigorous
results strongly suggest that relativistic X-ray disk lines can drive future
explorations of General Relativity and disk physics.Comment: 40 pages, includes color figures, to appear in ARAA, vol 45, in pres
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