A chandra/hetgs census of X-ray variability from Sgr A* during 2012

J. Neilsen, M. A. Nowak, C. Gammie, J. Dexter, S. Markoff, D. Haggard, S. Nayakshin, Q. D. Wang, N. Grosso, D. Porquet, J. A. Tomsick, N. Degenaar, P. C. Fragile, J. C. Houck, R. Wijnands, J. M. Miller, F. K. Baganoff

Research output: Contribution to journalArticlepeer-review


We present the first systematic analysis of the X-ray variability of Sgr A* during the Chandra X-ray Observatory's 2012 Sgr A* X-ray Visionary Project. With 38 High Energy Transmission Grating Spectrometer observations spaced an average of 7 days apart, this unprecedented campaign enables detailed study of the X-ray emission from this supermassive black hole at high spatial, spectral and timing resolution. In 3 Ms of observations, we detect 39 X-ray flares from Sgr A*, lasting from a few hundred seconds to approximately 8 ks, and ranging in 2-10 keV luminosity from 1034 erg s-1 to 2 × 1035 erg s-1. Despite tentative evidence for a gap in the distribution of flare peak count rates, there is no evidence for X-ray color differences between faint and bright flares. Our preliminary X-ray flare luminosity distribution dN/dL is consistent with a power law with index ; this is similar to some estimates of Sgr A*'s near-IR flux distribution. The observed flares contribute one-third of the total X-ray output of Sgr A* during the campaign, and as much as 10% of the quiescent X-ray emission could be comprised of weak, undetected flares, which may also contribute high-frequency variability. We argue that flares may be the only source of X-ray emission from the inner accretion flow.

Original languageEnglish (US)
Article number42
JournalAstrophysical Journal
Issue number1
StatePublished - Sep 1 2013


  • accretion, accretion disks
  • black hole physics
  • radiation mechanisms: non-thermal

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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