Journal Article

Coronal radiation of a cusp of spun-up stars and the X-ray luminosity of Sgr A*

S. Sazonov, R. Sunyaev and M. Revnivtsev

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 420, issue 1, pages 388-404
Published in print February 2012 | ISSN: 0035-8711
Published online January 2012 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2011.20043.x
Coronal radiation of a cusp of spun-up stars and the X-ray luminosity of Sgr A*

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Chandra has detected optically-thin, thermal X-ray emission with a size of ∼1 arcsec and luminosity ∼1033 erg s−1 from the direction of the Galactic supermassive black hole (SMBH), Sgr A*. We suggest that a significant or even dominant fraction of this signal may be produced by several thousand late-type main-sequence stars that possibly hide in the central ∼0.1 pc region of the Galaxy. As a result of tidal spin-ups caused by close encounters with other stars and stellar remnants, these stars should be rapidly rotating and hence have hot coronae, emitting copious amounts of X-ray emission with temperatures kT≲ a few keV. The Chandra data thus place an interesting upper limit on the space density of (currently unobservable) low-mass main-sequence stars near Sgr A*. This bound is close to and consistent with current constraints on the central stellar cusp provided by infrared observations. If coronally active stars do provide a significant fraction of the X-ray luminosity of Sgr A*, then it should be moderately variable on hourly and daily time-scales due to giant flares occurring on different stars. Another consequence is that the quiescent X-ray luminosity and accretion rate of the SMBH are yet lower than believed before.

Keywords: stars: coronae; Galaxy: centre; X-rays: stars

Journal Article.  15564 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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