A Caltech Library Service

Unveiling the disc structure in ultraluminous X-ray source NGC 55 ULX-1

Barra, F. and Pinto, C. and Walton, D. J. and Kosec, P. and D’Aì, A. and Di Salvo, T. and Del Santo, M. and Earnshaw, H. and Fabian, A. C. and Fuerst, F. and Marino, A. and Pintore, F. and Robba, A. and Roberts, T. P. (2022) Unveiling the disc structure in ultraluminous X-ray source NGC 55 ULX-1. Monthly Notices of the Royal Astronomical Society, 516 (3). pp. 3972-3983. ISSN 0035-8711. doi:10.1093/mnras/stac2453.

Full text is not posted in this repository. Consult Related URLs below.

Use this Persistent URL to link to this item:


Ultraluminous X-ray sources (ULXs) are the most extreme among X-ray binaries in which the compact object, a neutron star or a black hole, accretes matter from the companion star, and exceeds a luminosity of $10^{39} \ \rm erg \, s^{-1}$ in the X-ray energy band alone. Despite two decades of studies, it is still not clear whether ULX spectral transitions are due to stochastic variability in the wind or variations in the accretion rate or in the source geometry. The compact object is also unknown for most ULXs. In order to place constraints on to such scenarios and on the structure of the accretion disc, we studied the temporal evolution of the spectral components of the variable source NGC 55 ULX-1. Using recent and archival data obtained with the XMM-Newton satellite, we modelled the spectra with two blackbody components which we interpret as thermal emission from the inner accretion flow and the regions around or beyond the spherization radius. The luminosity–temperature (L–T) relation of each spectral component agrees with the L ∝ T4 relationship expected from a thin disc model, which suggests that the accretion rate is close to the Eddington limit. However, there are some small deviations at the highest luminosities, possibly due to an expansion of the disc and a contribution from the wind at higher accretion rates. Assuming that such deviations are due to the crossing of the Eddington or supercritical accretion rate, we estimate a compact object mass of 6–14 M⊙, favouring a stellar-mass black hole as the accretor.

Item Type:Article
Related URLs:
URLURL TypeDescription
Pinto, C.0000-0003-2532-7379
Walton, D. J.0000-0001-5819-3552
D’Aì, A.0000-0002-5042-1036
Di Salvo, T.0000-0002-3220-6375
Del Santo, M.0000-0002-1793-1050
Earnshaw, H.0000-0001-5857-5622
Fabian, A. C.0000-0002-9378-4072
Pintore, F.0000-0002-3869-2925
Robba, A.0000-0002-4107-8475
Roberts, T. P.0000-0001-8252-6337
Additional Information:This work is based on observations obtained with XMM-Newton, an ESA science mission funded by ESA Member States and USA (NASA). This work has been partially supported by the ASI-INAF program I/004/11/4 from the agreement ASI-INAF n.2017-14-H.0 and from the INAF mainstream grant. We acknowledge the XMM-Newton SOC for the great support in scheduling our observations. AM acknowledges a financialsupport from the agreement ASI-INAF n.2017-14-H.0 (PI: T. Belloni, A. De Rosa), the HERMES project by the Italian Space Agency (ASI) n. 2016/13 U.O, the H2020 ERC Consolidator Grant ‘MAGNESIA’ No. 817661 (PI: Rea) and National Spanish grant PGC2018-095512-BI00.
Funding AgencyGrant Number
Issue or Number:3
Record Number:CaltechAUTHORS:20221007-241666700.1
Persistent URL:
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:117284
Deposited By: Research Services Depository
Deposited On:14 Oct 2022 14:49
Last Modified:14 Oct 2022 14:49

Repository Staff Only: item control page