Pulsars, transients and relativistic astrophysics

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Nine-hour X-ray quasi-periodic eruptions from a low-mass black hole galactic nucleus

(2019)

Authors:

G Miniutti, RD Saxton, M Giustini, KD Alexander, RP Fender, I Heywood, I Monageng, M Coriat, AK Tzioumis, AM Read, C Knigge, P Gandhi, ML Pretorius, B Agís-González
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SN2018kzr: a rapidly declining transient from the destruction of a white dwarf

(2019)

Authors:

Owen R McBrien, Stephen J Smartt, Ting-Wan Chen, Cosimo Inserra, James H Gillanders, Stuart A Sim, Anders Jerkstrand, Armin Rest, Stefano Valenti, Rupak Roy, Mariusz Gromadzki, Stefan Taubenberger, Andreas Flörs, Mark E Huber, Ken C Chambers, Avishay Gal-Yam, David R Young, Matt Nicholl, Erkki Kankare, Ken W Smith, Kate Maguire, Ilya Mandel, Simon Prentice, Ósmar Rodríguez, Jonathon Pineda Garcia, Claudia P Gutiérrez, Lluís Galbany, Cristina Barbarino, Peter SJ Clark, Jesper Sollerman, Shrinivas R Kulkarni, Kishalay De, David AH Buckley, Arne Rau
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A public relativistic transfer function model for X-ray reverberation mapping of accreting black holes

Monthly Notices of the Royal Astronomical Society Oxford University Press (OUP) 488:1 (2019) 324-347

Authors:

Adam Ingram, Guglielmo Mastroserio, Thomas Dauser, Pieter Hovenkamp, Michiel van der Klis, Javier A García

Abstract:

ABSTRACT We present the publicly available model reltrans that calculates the light-crossing delays and energy shifts experienced by X-ray photons originally emitted close to the black hole when they reflect from the accretion disc and are scattered into our line of sight, accounting for all general relativistic effects. Our model is fast and flexible enough to be simultaneously fit to the observed energy-dependent cross-spectrum for a large range of Fourier frequencies, as well as to the time-averaged spectrum. This not only enables better geometric constraints than only modelling the relativistically broadened reflection features in the time-averaged spectrum, but additionally enables constraints on the mass of supermassive black holes in active galactic nuclei and stellar-mass black holes in X-ray binaries. We include a self-consistently calculated radial profile of the disc ionization parameter and properly account for the effect that the telescope response has on the predicted time lags. We find that a number of previous spectral analyses have measured artificially low source heights due to not accounting for the former effect and that timing analyses have been affected by the latter. In particular, the magnitude of the soft lags in active galactic nuclei may have been underestimated, and the magnitude of lags attributed to thermal reverberation in X-ray binaries may have been overestimated. We fit reltrans to the lag-energy spectrum of the Seyfert galaxy Mrk 335, resulting in a best-fitting black hole mass that is smaller than previous optical reverberation measurements (∼7 million compared with ∼14–26 million M⊙).
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Accretion and outflow in V404 Cyg

Monthly Notices of the Royal Astronomical Society Oxford University Press (OUP) 488:1 (2019) 1356-1365

Authors:

J Casares, T Muñoz-Darias, D Mata Sánchez, PA Charles, MAP Torres, M Armas Padilla, RP Fender, J García-Rojas
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An X-ray reverberation mass measurement of Cygnus X-1

Monthly Notices of the Royal Astronomical Society Oxford University Press (OUP) 488:1 (2019) 348-361

Authors:

Guglielmo Mastroserio, Adam Ingram, Michiel van der Klis

Abstract:

ABSTRACT We present the first X-ray reverberation mass measurement of a stellar-mass black hole. Accreting stellar-mass and supermassive black holes display characteristic spectral features resulting from reprocessing of hard X-rays by the accretion disc, such as an Fe Kα line and a Compton hump. This emission probes the innermost region of the accretion disc through general relativistic distortions to the line profile. However, these spectral distortions are insensitive to black hole mass, since they depend on disc geometry in units of gravitational radii. Measuring the reverberation lag resulting from the difference in path-length between direct and reflected emission calibrates the absolute length of the gravitational radius. We use a relativistic model able to reproduce the behaviour of the lags as a function of energy for a wide range of variability time-scales, addressing both the reverberation lags on short time-scales and the intrinsic hard lags on longer time-scales. We jointly fit the time-averaged spectrum and the real and imaginary parts of the cross-spectrum as a function of energy for a range of Fourier frequencies to Rossi X-ray Timing Exporer data from the X-ray binary Cygnus X-1. We also show that introducing a self-consistently calculated radial ionisation profile in the disc improves the fit, but requires us to impose an upper limit on ionization profile peak to allow a plausible value of the accretion disc density. This limit leads to a mass value more consistent with the existing dynamical measurement.
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