Low angular momentum accretion-outflow model of flares from Sgr A$^$.pdf

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Low angular momentum accretion-outflow model of flares from Sgr A$^$.pdf

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Low angular momentum accretion-outflow model of flares from Sgr A$^$

a r X i v : a s t r o - p h / 0 4 0 8 4 1 6 v 1 2 3 A u g 2 0 0 4 Mon. Not. R. Astron. Soc. 000, 000–000 (0000) Printed 2 February 2008 (MN LATEX style file v1.4) Low angular momentum accretion-outflow model of flares from Sgr A? Tapas K. Das1, Bozena Czerny1 1N. Copernicus Astronomical Center, Bartycka 18, 00-716 Warsaw, Poland tapas@camk.edu.pl, bcz@camk.edu.pl 2 February 2008 ABSTRACT We employ a low angular momentum accretion-outflow scenario to model the flares emanating out from the central region of Sgr A?. The primary donor for matter ac- creting onto the central SMBH of Sgr A? is assumed to be the WR star ISR 13 E3. We analytically calculate the specific energy and angular momentum density of stel- lar wind originating from ISR 13 E3 and study the dynamics of that wind down to the very close vicinity of the central SMBH of Sgr A?. We show that on the way to the Galactic centre, such wind-fed accretion may encounter standing shocks and such shock drives outflow from the close vicinity of the SMBH. Matter content of such out- flow is computed and it is argued that such outflow is responsible for production of the Galactic centre flares. We then self-consistently compute the luminosity Lj and the duration time scale τ of such flares, as a function of fundamental accretion parame- ters. Our theoretical calculation of Lj and τ are in good agreement with observational results. Key words: Galaxy:center - accretion, accretion discs - black hole physics - hydro- dynamics 1 INTRODUCTION The center of our Galaxy harbors a massive black hole, and the surrounding region including the central SMBH is now customarily referred as Sgr A* as a whole, after the radio source first discovered at that location (for a review, see e.g. Melia Falcke 2001). Sgr A* shows frequent flares originat- ing from the direct vicinity of the central black hole. In the X-ray band, multiple flares are superimposed on a steady, extended emission at the level of ～ 2.2× 1033 erg s?1 cm?2 (Bag