Jifeng Liu, Jerome Orosz, Joel N. Bregman
Dynamical mass measurements hold the key to answering whether ultraluminous
X-ray sources (ULXs) are intermediate mass black holes (IMBHs) or stellar mass
black holes with special radiation mechanisms. NGC 1313 X-2 is so far the only
ULX with HST light curves, the orbital period, and the black hole's radial
velocity amplitude based on the He II $\lambda4686$\AA\ disk emission line
shift of $\sim200$ km/s. We constrain its black hole mass and other parameters
by fitting observations to a binary light curve code with accommodations for
X-ray heating of the accretion disk and the secondary. Given the dynamical
constraints from the observed light curves and the black hole radial motion and
the observed stellar environment age, the only acceptable models are those with
40-50 Myrs old intermediate mass secondaries in their helium core and hydrogen
shell burning phase filling 40%-80% of their Roche lobes. The black hole can be
a massive black hole of a few tens of $M_\odot$ that can be produced from
stellar evolution of low metalicity stars, or an IMBH of a few hundred to above
1000$M_\odot$ if its true radial velocity $2K^\prime<40$ km/s. Further
observations are required to better measure the black hole radial motion and
the light curves in order to determine whether NGC 1313 X-2 is a stellar black
hole or an IMBH.
View original:
http://arxiv.org/abs/1110.5708
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