EDP Sciences
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Volume 397, Number 1, January I 2003
Page(s) 121 - 125
Section Galactic structure and dynamics
DOI http://dx.doi.org/10.1051/0004-6361:20021482

A&A 397, 121-125 (2003)
DOI: 10.1051/0004-6361:20021482

On the central black hole mass in Mkn 501

F. M. Rieger1, 2 and K. Mannheim1

1  Institut für Theoretische Physik und Astrophysik der Universität Würzburg, Am Hubland, 97074 Würzburg, Germany
    e-mail: frieger@uni-sw.gwdg.de;mannheim@astro.uni-wuerzburg.de
2  Universitäts-Sternwarte Göttingen, Geismarlandstr. 11, 37083 Göttingen, Germany

(Received 17 June 2002 / Accepted 8 October 2002)

We analyse the apparent disagreement between the mass estimates of the central black hole(s) in Mkn 501 based on (i) the observations of the host galaxy, (ii) the high energy (HE) emission mechanism, and (iii) the modulation of the beamed radiation by a black hole (BH) binary system. While method (i) seems to imply a central mass $\ga$ $ 5\times 10^8\,
M_{\odot}$ , method (ii) suggests a BH mass less than $\simeq$ $
6 \times 10^7\, M_{\odot}$ . We critically discuss the estimates inferred from (i) showing that current uncertainties may permit a central mass as low as $\simeq$(2- $3)\times 10^8\,M_{\odot}$. We demonstrate that in this case the estimates (i) and (ii) might be brought into agreement by assuming a binary BH system where the jet dominating the HE emission originates from the less massive (secondary) BH as suggested by method (iii). On the other hand, if Mkn 501 has in fact a high central BH mass of order $10^9\, M_{\odot}$, a change of fundamental assumptions seems to be required in the context of several HE emission models. We show, that in this case a binary scenario following (iii) may be still possible if the jet which dominates the emission emerges from the more massive (primary) BH and if the binary evolution passes through phases of super-Eddington accretion and/or decreased conversion efficiency.

Key words: BL Lacertae objects: individual: Mkn 501 -- galaxies: jets -- black hole physics

Offprint request: F. M. Rieger, frieger@uni-sw.gwdg.de

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