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A CHANDRA/HETGS CENSUS OF X-RAY VARIABILITY FROM Sgr A* DURING 2012

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posted on 16.12.2016, 11:41 by 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
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 −1.9+0.3 −0.4; 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.

Funding

We acknowledge the role of the Lorentz Center, Leiden, and the Netherlands Organization for Scientific Research Vidi Fellowship 639.042.711 (S.M.). J.N. gratefully acknowledges funding support from NASA through the Einstein Postdoctoral Fellowship, grant PF2-130097, awarded by the Chandra X-ray Center, which is operated by the Smithsonian Astrophysical Observatory for NASA under contract NAS8-03060, and from NASA through the Smithsonian Astrophysical Observatory contract SV3-73016 to MIT for support of the Chandra X-ray Center, which is operated by the Smithsonian Astrophysical Observatory for and on behalf of NASA under contract NAS8-03060. F.K.B. acknowledges support from the Chandra grant G02-13110A under contract NAS8-03060. N.D. is supported by NASA through Hubble Postdoctoral Fellowship grant number HST-HF-51287.01-A. R.W. was partly supported by an European Research Council starting grant.

History

Citation

Astrophysical Journal, 774:42 (14pp), 2013 September 1

Author affiliation

/Organisation/COLLEGE OF SCIENCE AND ENGINEERING/Department of Physics and Astronomy

Version

VoR (Version of Record)

Published in

Astrophysical Journal

Publisher

American Astronomical Society, IOP Publishing

issn

0004-637X

eissn

1538-4357

Acceptance date

25/07/2013

Available date

16/12/2016

Publisher version

http://iopscience.iop.org/article/10.1088/0004-637X/774/1/42/meta

Language

en