Journal Article

Accurate positions for the ultraluminous X-ray sources NGC 7319-X4 and NGC 5474-X1 and limiting magnitudes for their optical counterparts

M. Heida, P. G. Jonker, M. A. P. Torres and S. Mineo

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 424, issue 2, pages 1563-1569
Published in print August 2012 | ISSN: 0035-8711
Published online August 2012 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2012.21370.x
Accurate positions for the ultraluminous X-ray sources NGC 7319-X4 and NGC 5474-X1 and limiting magnitudes for their optical counterparts

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Abstract

In this paper, we report accurate Chandra positions for two ultraluminous X-ray sources (ULXs): NGC 7319-X4 at Right Ascension (RA) = 339°.029 17(2), Declination (Dec.) = 33°.974 76(2) and NGC 5474-X1 at RA = 211°.248 59(3), Dec. = 53°.635 84(3). We perform bore-sight corrections on the Chandra X-ray satellite observations of these sources to get these accurate positions of the X-ray sources and match these positions with archival optical data from the Wide Field Planetary Camera 2 (WFPC2) onboard 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 find evidence for X-ray variability in NGC 5474-X1. Finally, we briefly discuss several options for the nature of these ULXs.

Keywords: galaxies: individual: NGC 5474; galaxies: individual: NGC 7319; X-rays: binaries; X-rays: individual: NGC 5474-X1; X-rays: individual: NGC 7319-X4

Journal Article.  5089 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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