We use cookies to ensure that we give you the best experience on our website. You can change your cookie settings at any time. Otherwise, we'll assume you're OK to continue.

Durham University

Department of Physics

Staff profile

Publication details for Prof Tim Roberts

Stobbart, A-M., Roberts, T. P. & Wilms, J. (2006). XMM-Newton observations of the brightest ultraluminous X-ray sources. Monthly Notices of the Royal Astronomical Society 368(1): 397-413.

Author(s) from Durham


We present an analysis of 13 of the best quality ultraluminous X-ray source (ULX) data sets available from XMM-Newton European Photon Imaging Camera (EPIC) observations. We utilize the high signal-to-noise in these ULX spectra to investigate the best descriptions of their spectral shape in the 0.3-10 keV range. Simple models of an absorbed power law or multicolour disc blackbody prove inadequate at describing the spectra. Better fits are found using a combination of these two components, with both variants of this model - a cool (~0.2 keV) disc blackbody plus hard power-law continuum, and a soft power-law continuum, dominant at low energies, plus a warm (~1.7 keV) disc blackbody - providing good fits to 8/13 ULX spectra. However, by examining the data above 2 keV, we find evidence for curvature in the majority of data sets (8/13 with at least marginal detections), inconsistent with the dominance of a power law in this regime. In fact, the most successful empirical description of the spectra proved to be a combination of a cool (~0.2 keV) classic blackbody spectrum, plus a warm disc blackbody that fits acceptably to 10/13 ULXs. The best overall fits are provided by a physically self-consistent accretion disc plus Comptonized corona model (DISKPN + EQPAIR), which fits acceptably to 11/13 ULXs. This model provides a physical explanation for the spectral curvature, namely that it originates in an optically thick corona, though the accretion disc photons seeding this corona still originate in an apparently cool disc. We note similarities between this fit and models of Galactic black hole binaries at high accretion rates, most notably the model of Done & Kubota. In this scenario the inner disc and corona become energetically coupled at high accretion rates, resulting in a cooled accretion disc and optically thick corona. We conclude that this analysis of the best spectral data for ULXs shows it to be plausible that the majority of the population are high accretion rate stellar-mass (perhaps up to 80 solar mass) black holes, though we cannot categorically rule out the presence of larger, ~1000 solar mass intermediate-mass black holes (IMBHs) in individual sources with the current X-ray data.


Anders E., Grevesse N., 1989, Geochim. Cosmochim. Acta, 53, 197
Balucinska-Church M., McCammon D., 1992, ApJ, 400, 699
Begelman M. C., 2002, ApJ, 568, L97
Belczynski K., Sadowski A., Rasio F. A., 2004, ApJ, 611, 1068
Belloni T., M´endez M., van der Klis M., Lewin W. H. G., Dieters S., 1999,
ApJ, 519, L159
Colbert E. J. M., Mushotzky R. F., 1999, ApJ, 519, 89
Colbert E. J. M., Ptak A. F., 2002, ApJS, 143, 25
Colbert E. J. M., Petre R., Schlegel E. M., Ryder S. D., 1995, ApJ, 446, 177
Coppi P. S., 1999, in Poutanen J., Svensson R., eds, ASP Conf. Ser. Vol. 161,
High Energy Processes in Accreting Black Holes. Astron Soc. Pac., San
Francisco, p. 375
Cropper M., Soria R., Mushotzky R. F.,Wu K., Markwardt C. B., Pakull M.,
2004, MNRAS, 349, 39
Crummy J., Fabian A. C., Gallo L., Ross R. R., 2006, MNRAS, 365, 1067
Dewangan G. C., Miyaji T., Griffiths R. E., Lehmann I., 2004, ApJ, 608,
Dickey J. M., Lockman F. J., 1990, ARA&A, 28, 215
Done C., Gierli´nski M., 2005, MNRAS, 364, 208
Done C., Kubota A., 2005, MNRAS submitted (astro-ph/0511030)
Ebisawa K., ˙ Zycki P., Kubota A., Mizuno T., Watarai K., 2003, ApJ, 597,
Ehle M., Pietsch W., Beck R., Klein U., 1998, A&A, 329, 39
Fabbiano G., 1988, ApJ, 325, 544
Fabbiano G., 1989, ARA&A, 27, 87
Falcke H., Biermann P. L., 1995, A&A, 293, 665
Feng H., Kaaret P., 2005, ApJ, 633, 1052
Foschini L., Rodriguez J., Fuchs Y., Ho L. C., Dadina M., Di Cocco G.,
Courvoisier T. J.-L., Malaguti G., 2004, A&A, 416, 529
Fryer C. L., Kalogera V., 2001, ApJ, 554, 548
Gao Y., Wang Q. D., Appleton P. N., Lucas R. A., 2003, ApJ, 596, L171
Gierli´nski M., Zdziarski A. A., Poutanen J., Coppi P. S., Ebisawa K., Johnson
W. N., 1999, MNRAS, 309, 496
Gilfanov M., Grimm H.-J., Sunyaev R., 2004, Nucl. Phys. Sect. B Suppl.,
132, 369
Goad M. R., Roberts T. P., Knigge C., Lira P., 2002, MNRAS, 335, L67
Goad M. R., Roberts T. P., Reeves J., Uttley P., 2006, MNRAS, 365, 191
Grimm H.-J., Gilfanov M., Sunyaev R., 2003, MNRAS, 339, 793
Haardt F. et al., 2001, ApJS, 133, 187
Ho L. C., Filippenko A. V., Sargent W. L. W., 1997, ApJS, 112, 315
Immler S., Wang Q. D., 2001, ApJ, 554, 202
Immler S., Vogler A., Ehle M., Pietsch W., 1999, A&A, 352, 415
Jonker P. G., Nelemans G., 2004, MNRAS, 354, 355
Kaaret P., Corbel S., Prestwich A. H., Zezas A., 2003, Sci, 299, 365
Kaaret P., Ward M. J., Zezas A., 2004, MNRAS, 351, L83
Karachentsev I. D. et al., 2003, A&A, 404, 93
King A. R., 2004, MNRAS, 347, L18
King A. R., Dehnen W., 2005, MNRAS, 357, 275
King A. R., Pounds K. A., 2003, MNRAS, 345, 657
King A. R., Davies M. B., Ward M. J., Fabbiano G., Elvis M., 2001, ApJ,
552, L109
K¨ording E., Falcke H., Markoff S., 2002, A&A, 382, L13
K¨ording E., Colbert E., Falcke H., 2005, A&A, 436, 427
Krolik J. H., 2004, ApJ, 615, 383
Lira P., Lawrence A., Johnson R. A., 2000, MNRAS, 319, 17
Liu J., Bregman J. N., 2005, ApJS, 157, 59
Liu J., Bregman J. N., Seitzer P., 2004, ApJ, 602, 249
Makishima K., MaejimaY., Mitsuda K., Bradt H.V., Remillard R. A., Tuohy
I. R., Hoshi R., Nakagawa M., 1986, ApJ, 308, 635
Makishima K. et al., 2000, ApJ, 535, 632
Markert T. H., Rallis A. D., 1983, ApJ, 275, 571
Markoff S., Falcke H., Fender R., 2001, A&A, 372, L25
Markoff S., Nowak M. A., Wilms J., 2005, ApJ, 635, 1203
Martocchia A., Matt G., Belloni T., Feroci M., Karas V., Ponti G., 2006,
A&A, 448, 677
McClintock J. E., Remillard R. A., 2003, in LewinW. H. G., van der Klis M.,
eds, Compact Stellar X-ray Sources. Cambridge Univ. Press, Cambridge,
in press (astro-ph/0306213)
McClintock J. E. et al., 2001, ApJ, 555, 477
Miller M. C., Colbert E. J. M., 2004, Int. J. Mod. Phys. D, 13, 1
Miller J. M., Fabbiano G., Miller M. C., Fabian A. C., 2003, ApJ, 585, L37
Miller J. M., Fabian A. C., Miller M. C., 2004a, ApJ, 607, 931
Miller J. M., Fabian A. C., Miller M. C., 2004b, ApJ, 614, L117
Misra R., Chitnis V. R., Melia F., 1998, ApJ, 495, 407
Mitsuda K. et al., 1984, PASJ, 36, 741
Miyaji T., Lehmann I., Hasinger G., 2001, AJ, 121, 3041
Mucciarelli P., Casella P., Belloni T., Zampieri L., Ranalli P., 2006, MNRAS,
365, 1123
Nayakshin S., Melia F., 1997, ApJ, 490, L13
Paturel G., Theureau G., Fouqu´e P., Terry J. N., Musella I., Ekholm T., 2002,
A&A, 383, 398
Pietsch W., Mochejska B. J., Misanovic Z., Haberl F., Ehle M., Trinchieri
G., 2004, A&A, 413, 879
Portegies Zwart S. F., Baumgardt H., Hut P., Makino J., McMillan S. L.W.,
2004, Nat, 428, 724
Radecke H.-D., 1997, A&A, 319, 18
Ramsey C. J., Williams R. M., Gruendl R. A., Chen C.-H. R., Chu Y.-H.,
Wang Q. D., 2006, ApJ, in press (astro-ph/0511540)
Read A. M., Ponman T. J., Strickland D. K., 1997, MNRAS, 286, 626
Roberts T. P., Colbert E. J. M., 2003, MNRAS, 341, L49
Roberts T. P., Warwick R. S., 2000, MNRAS, 315, 98
Roberts T. P.,Warwick R. S.,Ward M. J., Murray S. S., 2002, MNRAS, 337,
Roberts T. P.,Warwick R. S.,Ward M. J., Goad M. R., 2004, MNRAS, 349,
Roberts T. P., Warwick R. S., Ward M. J., Goad M. R., Jenkins L. P., 2005,
MNRAS, 357, 1363
Schlegel E. M., Pannuti T. G., 2003, AJ, 125, 3025
Schlegel E. M., Barrett P., Singh K. P., 1997, AJ, 113, 1296
Schlegel E. M., Petre R., Colbert E. J. M., Miller S., 2000, AJ, 120, 2373
Shakura N. I., Sunyaev R. A., 1973, A&A, 24, 337
Shrader C. R., Titarchuk L., 2003, ApJ, 598, 168
Soria R., Wu K., 2002, A&A, 384, 99
Stobbart A.-M., Roberts T. P., Warwick R. S., 2004, MNRAS, 351, 1063
Strickland D. K., Colbert E. J. M., Heckman T. M., Weaver K. A., Dahlem
M., Stevens I. R., 2001, ApJ, 560, 707
Strohmayer T. E., Mushotzky R. F., 2003, ApJ, 568, L61
Str¨uder L. et al., 2001, A&A, 365, L18.
Swartz D. A., Ghosh K. K., Tennant A. F., Wu K., 2004, ApJS, 154, 519
Terashima Y., Wilson A. S., 2004, ApJ, 601, 735
Trinchieri G., Fabbiano G., Paulumbo G. G. C., 1985, ApJ, 290, 96
Tully R. B., 1988, Nearby Galaxies Catalog. Cambridge Univ. Press,
Turner M. J. L. et al., 2001, A&A, 365, L27
van der Klis M., 1995, in Lewin W. H. G., van Paradijs J., van den Heuvel
E. P. J., eds, X-Ray Binaries. Cambridge Univ. Press, Cambridge, p. 252
Vaughan S., Iwasawa K., Fabian A. C., Hayashida K., 2005, MNRAS, 356,
Vogler A., Pietsch W., Bertoldi F., 1997, A&A, 318, 768
Wang Q. D., Yao Y., Fukui W., Zhang S. N., Williams R., 2004, ApJ, 609,
Wilms J., Nowak M. A., Dove J. B., Fender R. P., di Matteo T., 1999, ApJ,
522, 460
Zampieri L., Mucciarelli P., Falomo R., Kaaret P., Di Stefano R., Turolla R.,
Chieregato M., Treves A., 2004, ApJ, 603, 523
Zezas A., Fabbiano G., Rots A. H., Murray S. S., 2002a, ApJS, 142, 239
Zezas A., Fabbiano G., Rots A. H., Murray S. S., 2002b, ApJ, 577, 710
Zhang S. N., Cui W., Chen W., Yao Y., Zhang X., Sun X., Wu X., Xu H.,
2000, Sci, 287, 1239.