All Outputs (6)

Origins of the UV/X-ray relation in Arakelian 120 (2022)
Journal Article
Mahmoud, R. D., Done, C., Porquet, D., & Lobban, A. (2023). Origins of the UV/X-ray relation in Arakelian 120. Monthly Notices of the Royal Astronomical Society, 521(3), 3585-3596. https://doi.org/10.1093/mnras/stac3809

We explore the accretion geometry in Arakelian 120 using intensive UV and X-ray monitoring from Swift. The hard X-rays (1–10 keV) show large amplitude, fast (few-day) variability, so we expect reverberation from the disc to produce UV variability fro... Read More about Origins of the UV/X-ray relation in Arakelian 120.

Looking for the underlying cause of black hole X-ray variability in GRMHD simulations (2020)
Journal Article
White, C., Narayan, R., Kluźniak, W., Fragile, P., Done, C., Mahmoud, R., & Bollimpalli, D. (2020). Looking for the underlying cause of black hole X-ray variability in GRMHD simulations. Monthly Notices of the Royal Astronomical Society, 496(3), 3808-3828. https://doi.org/10.1093/mnras/staa1808

Long-term observations have shown that black hole X-ray binaries exhibit strong, aperiodic variability on time-scales of a few milliseconds to seconds. The observed light curves display various characteristic features like a lognormal distribution of... Read More about Looking for the underlying cause of black hole X-ray variability in GRMHD simulations.

Discarding the disc in a changing-state AGN: the UV/X-ray relation in NGC 4151 (2019)
Journal Article
Mahmoud, R. D., & Done, C. (2020). Discarding the disc in a changing-state AGN: the UV/X-ray relation in NGC 4151. Monthly Notices of the Royal Astronomical Society, 491(4), 5126-5139. https://doi.org/10.1093/mnras/stz3196

Recent monitoring campaigns designed to map the accretion regime in AGN show major discrepancies with models where the optical/ultraviolet (UV) is produced by X-ray-illuminated, optically thick disc material within a few hundred gravitational radii.... Read More about Discarding the disc in a changing-state AGN: the UV/X-ray relation in NGC 4151.

Reverberation Reveals the Truncated Disc in the Hard State of GX 339-4 (2019)
Journal Article
Mahmoud, R. D., Done, C., & De Marco, B. (2019). Reverberation Reveals the Truncated Disc in the Hard State of GX 339-4. Monthly Notices of the Royal Astronomical Society, 486(2), 2137-2152. https://doi.org/10.1093/mnras/stz933

The nature and geometry of the hard state in black hole binaries is controversial. The broadband continuum spectrum and fast variability properties can be explained in a model where the inner disc evaporates into a geometrically thick, hot flow. Howe... Read More about Reverberation Reveals the Truncated Disc in the Hard State of GX 339-4.

A physical model for the spectral-timing properties of accreting black holes (2018)
Journal Article
Mahmoud, R. D., & Done, C. (2018). A physical model for the spectral-timing properties of accreting black holes. Monthly Notices of the Royal Astronomical Society, 480(3), 4040-4059. https://doi.org/10.1093/mnras/sty2133

We develop new techniques to deconvolve the radial structure of the X-ray emission region in the bright low/hard state of the black hole Cygnus X-1 using both spectral and timing data in the 3–35 keV range. The spectrum at these energies is dominated... Read More about A physical model for the spectral-timing properties of accreting black holes.

Modelling the energy dependence of black hole binary flows (2017)
Journal Article
Mahmoud, R. D., & Done, C. (2018). Modelling the energy dependence of black hole binary flows. Monthly Notices of the Royal Astronomical Society, 473(2), 2084-2097. https://doi.org/10.1093/mnras/stx2359

We build a full spectral-timing model for the low/hard state of black hole binaries assuming that the spectrum of the X-ray hot flow can be produced by two Comptonization zones. Slow fluctuations generated at the largest radii/softest spectral region... Read More about Modelling the energy dependence of black hole binary flows.