Accurate positions for the ultraluminous X-ray sources NGC 7319-X4 and NGC 5474-X1 and limiting magnitudes for their optical counterparts
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.
- Publication:
-
Monthly Notices of the Royal Astronomical Society
- Pub Date:
- August 2012
- DOI:
- 10.1111/j.1365-2966.2012.21370.x
- arXiv:
- arXiv:1206.0597
- Bibcode:
- 2012MNRAS.424.1563H
- Keywords:
-
- galaxies: individual: NGC 5474;
- galaxies: individual: NGC 7319;
- X-rays: binaries;
- X-rays: individual: NGC 5474-X1;
- X-rays: individual: NGC 7319-X4;
- Astrophysics - High Energy Astrophysical Phenomena
- E-Print:
- 8 pages, 4 figures, accepted for publication in MNRAS