Chandra and swift follow-up observations of the intermediate-mass black hole in ESO 243-49

Abstract

The brightest ultra-luminous X-ray source HLX-1 in the galaxy ESO 243-49 provides strong evidence for the existence of intermediate-mass black holes (IMBHs). As the luminosity and thus the mass estimate depend on the association of HLX-1 with ESO 243-49, it is essential to confirm its affiliation. This requires follow-up investigations at wavelengths other than X-rays, which in turn needs an improved source position. To further reinforce the IMBH identification, it is necessary to determine HLX-1's environment to establish whether it could potentially form and nourish a black hole at the observed luminosities. Using the High Resolution Camera on board Chandra, we determine a source position of R.A. = 01h10m283 and decl. = -46°04′223. A conservative 95% error of 03 was found following a boresight correction by cross-matching the positions of three X-ray sources in the field with the Two Micron All Sky Survey catalog. Combining all Swift UV/Optical Telescope uvw2 images, we failed to detect a UV source at the Chandra position down to a 3σ limiting magnitude of 20.25 mag. However, there is evidence that the UV emission is elongated in the direction of HLX-1. This is supported by archival data from GALEX and suggests that the far-UV emission is stronger than the near-UV. This could imply that HLX-1 may be situated near the edge of a star-forming region. Using the latest X-ray observations, we deduce the mass accretion rate of a 500 M black hole with the observed luminosity and show that this is compatible with such an environment. © 2010. The American Astronomical Society. All rights reserved..