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arXiv · 1206.0597

Accurate positions for the ULXs NGC 7319-X4 and NGC 5474-X1 and limiting magnitudes for their optical counterparts

M. Heida·P. G. Jonker·M. A. P. Torres·S. Mineo
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Abstract

In this paper we report accurate Chandra positions for two ultraluminous X-ray sources: NGC 7319-X4 at Right Ascension (RA) = 339.02917(2) deg, Declination (Dec) = 33.97476(2) deg and NGC 5474-X1 at RA = 211.24859(3) deg, Dec = 53.63584(3) deg. We perform bore-sight corrections on the Chandra X-ray Satellite observations of these sources to get to these accurate positions of the X-ray sources and match these positions with archival optical data from the Wide Field and Planetary Camera 2 on board the Hubble Space Telescope. We do not find the optical counterparts: the limiting absolute magnitudes of the observations in the WFPC2 standard magnitude system are B = -7.9, V = -8.7 and I = -9.3 for NGC 7319-X4 and U = -6.4 for NGC 5474-X1. We report on the X-ray spectral properties and we find evidence for X-ray variability in NGC 5474-X1. Finally, we briefly discuss several options for the nature of these ULXs.

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M. Heida, P. G. Jonker, M. A. P. Torres, S. Mineo. 2012-06-04. Accurate positions for the ULXs NGC 7319-X4 and NGC 5474-X1 and limiting magnitudes for their optical counterparts. https://doi.org/10.1111/j.1365-2966.2012.21370.x

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