OPTICAL COUNTERPARTS OF THE NEAREST ULTRALUMINOUS X-RAY SOURCES

Journal Article · Sat Jun 01 04:00:00 EDT 2013 · Astrophysical Journal, Supplement Series

DOI:https://doi.org/10.1088/0067-0049/206/2/14· OSTI ID:22156536

Gladstone, Jeanette C.; Heinke, Craig O.; Cartwright, Taylor F. ^[1]; Copperwheat, Chris ^[2]; Roberts, Timothy P. ^[3]; Levan, Andrew J. ^[4]

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1. Department of Physics, University of Alberta, 11322-89 Avenue, Edmonton, Alberta T6G 2G7 (Canada)
2. Department of Physics, Liverpool John Moores University, Wirral CH41 1LD (United Kingdom)
3. Department of Physics, University of Durham, South Road, Durham DH1 3LE (United Kingdom)
4. Department of Physics, University of Warwick, Coventry CV4 7VL (United Kingdom)

We present a photometric survey of the optical counterparts of ultraluminous X-ray sources (ULXs) observed with the Hubble Space Telescope (HST) in nearby ({approx}<5 Mpc) galaxies. Of the 33 ULXs with HST and Chandra data, 9 have no visible counterpart, placing limits on their M{sub V} of {approx} -4 to -9, enabling us to rule out O-type companions in 4 cases. The refined positions of two ULXs place them in the nucleus of their host galaxy. They are removed from our sample. Of the 22 remaining ULXs, 13 have one possible optical counterpart, while multiple are visible within the error regions of other ULXs. By calculating the number of chance coincidences, we estimate that 13 {+-} 5 are the true counterparts. We attempt to constrain the nature of the companions by fitting the spectral energy distribution and M{sub V} to obtain candidate spectral types. We can rule out O-type companions in 20 cases, while we find that one ULX (NGC 253 ULX2) excludes all OB-type companions. Fitting with X-ray irradiated models provides constraints on the donor star mass and radius. For seven ULXs, we are able to impose inclination-dependent upper and/or lower limits on the black holes' mass, if the extinction to the assumed companion star is not larger than the Galactic column. These are NGC 55 ULX1, NGC 253 ULX1, NGC 253 ULX2, NGC 253 XMM6, Ho IX X-1, IC342 X-1, and NGC 5204 X-1. This suggests that 10 ULXs do not have O companions, while none of the 18 fitted rule out B-type companions.

• OSTI ID: 22156536
• Journal Information: Astrophysical Journal, Supplement Series, Journal Name: Astrophysical Journal, Supplement Series Journal Issue: 2 Vol. 206; ISSN 0067-0049; ISSN APJSA2
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
ACCRETION DISKS
BLACK HOLES
ERRORS
GALAXIES
STARS
TELESCOPES
X RADIATION
X-RAY SOURCES