Paper: astro-ph/0601450
Date: Thu, 19 Jan 2006 19:54:52 GMT (16kb)

Title: Upper limits on the central black hole masses of 47Tuc and NGC6397

Authors: S. De Rijcke, P. Buyle, H. Dejonghe

Comments: 4 pages, 1 figure, accepted for publication by MNRAS
\\
We present upper-limits on the masses of the putative central
intermediate-mass black holes in two nearby Galactic globular clusters: 47Tuc
(NGC104), the second brightest Galactic globular cluster, and NGC6397, a
core-collapse globular cluster and, with a distance of 2.7 kpc, quite possibly
the nearest globular cluster, using a technique suggested by T. Maccarone.
These mass estimates have been derived from 3sigma upper limits on the radio
continuum flux at 1.4 GHz, assuming that the putative central black hole
accretes the surrounding matter at a rate between 0.1% and 1% of the Bondi
accretion rate. For 47Tuc, we find a 3sigma upper limit of 2060 - 670 solar
masses, depending on the actual accretion rate of the black hole and the
distance to 47Tuc. For NGC6397, which is closer to us, we derive a 3sigma upper
limit of 1290 - 390 solar masses. While estimating mass upper-limits based on
radio continuum observations requires making assumptions about the gas density
and the accretion rate of the black hole, their derivation does not require
complex and time consuming dynamical modeling. Thus, this method offers an
independent way of estimating black hole masses in nearby globular clusters.
If, generally, central black holes in stellar systems accrete matter faster
than 0.1% of the Bondi accretion rate, then these results indicate the absence
of black holes in these globular clusters with masses as predicted by the
extrapolated M-sigma relation.

\\ ( http://arXiv.org/abs/astro-ph/0601450 , 16kb)