Program: GN-2009B-Q-21

Title:Constraining the mass of the black hole within an ultraluminous X-ray source
PI:Timothy Roberts
Co-I(s): Jeanette Gladstone, Mike Goad, Andrew Levan, Mark Swinbank, Martin Ward

Abstract

The masses of the black holes that power ultraluminous X-ray sources (ULXs) have recently been a topic of intense debate, with some evidence pointing to the existence of a new class of intermediate-mass black holes (IMBHs), whilst other evidence suggested the presence of the most extreme accretors amongst stellar remnant black holes (possibly ranging in mass up to ~100 M(sun)). Despite recent attention, this puzzle remains essentially unresolved. Here we propose 10 GMOS-N observations of the optical counterpart to the nearby ULX Ho IX X-1, with the aim of obtaining radial velocity measurements based on its He II 4686A accretion disc emission line, characterised in our pilot GMOS study of this source. This will allow us to derive the first ever constraints on the mass function of a ULX, and hence the first dynamical mass for a black hole powering a ULX. *CONDITIONAL RE-SUBMISSION - SEE TECHNICAL FEASIBILITY*

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