Long-term variability of Cygnus X-1. IX. A spectral-timing comparison of Cygnus X-1 and MAXI J1820+070 in the hard state

Basak A, Uttley P, Bollemeijer N, Bachetti M, Bahramian A, Grinberg V, Kara E, Lai EV, Maccarone TJ, De Marco B, Miller-Jones J, Pottschmidt K, Vaughan SA, Wilms J (2025)

Publication Type: Journal article

Publication year: 2025

Journal

Monthly Notices of the Royal Astronomical Society Oxford University Press

Book Volume: 542

Pages Range: 982-997

Journal Issue: 2

DOI: 10.1093/mnras/staf1155

Abstract

Cygnus X-1 is a persistent, high-mass black hole X-ray binary (BHXRB) which in the hard state shows many similar properties to transient BHXRBs, along with intriguing differences, such as the lack of quasi-periodic oscillations. Here, we compare for the first time the detailed spectral-timing properties of Cyg X-1 with a transient BHXRB, MAXI J1820+070, combining data from XMM-Newton and NICER (Neutron Star Interior Composition Explorer) with contemporaneous INTEGRAL (International Gamma-Ray Astrophysics Laboratory) data to study the power spectra, rms spectra, and time lags over a broad 0.5-200 keV range. We select bright hard state MAXI J1820+070 data with similar power-spectral shapes to the Cyg X-1 data, to compare the source behaviours while accounting for the evolution of spectral-timing properties, notably the lags, through the hard state. Cyg X-1 shows no evidence for soft lags in the 1-10 Hz frequency range where they are clearly detected for MAXI J1820+070. Furthermore, the low-frequency hard lags and rms spectra evolve much more strongly during the hard state of Cyg X-1 than for MAXI J1820+070. We argue that these differences cannot be explained by the different black hole masses of these systems, but may be related to their different accretion rates and corresponding locations on the hardness-intensity diagram. We conjecture that there is a significant luminosity-dependence of coronal geometry in the hard state of BHXRBs, rather than an intrinsic difference between Cyg X-1 and transient BHXRBs. This possibility has also been suggested to explain a common time-lag feature that appears in the hard intermediate states of Cyg X-1 and transient BHXRBs.

Authors with CRIS profile

Jörn Wilms Professur für Astronomie und Astrophysik

Involved external institutions

University of Amsterdam NL Netherlands (NL) INAF-Osservatorio Astronomico di Cagliari IT Italy (IT) International Centre for Radio Astronomy Research AU Australia (AU) European Space Research and Technology Centre (ESTEC, ESA) NL Netherlands (NL) Massachusetts Institute of Technology (MIT) US United States (USA) (US) Texas Tech University (TTU) US United States (USA) (US) Polytechnic University of Catalonia / Universitat Politècnica de Catalunya · BarcelonaTech (UPC) / Universidad Politécnica de Cataluña ES Spain (ES) University of Maryland, Baltimore County (UMBC) US United States (USA) (US) University of Leicester GB United Kingdom (GB)

How to cite

APA:

Basak, A., Uttley, P., Bollemeijer, N., Bachetti, M., Bahramian, A., Grinberg, V.,... Wilms, J. (2025). Long-term variability of Cygnus X-1. IX. A spectral-timing comparison of Cygnus X-1 and MAXI J1820+070 in the hard state. Monthly Notices of the Royal Astronomical Society, 542(2), 982-997. https://doi.org/10.1093/mnras/staf1155

MLA:

Basak, Arkadip, et al. "Long-term variability of Cygnus X-1. IX. A spectral-timing comparison of Cygnus X-1 and MAXI J1820+070 in the hard state." Monthly Notices of the Royal Astronomical Society 542.2 (2025): 982-997.

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