STROBE-X: X-ray timing and spectroscopy on dynamical timescales from microseconds to years

Wilson-Hodge, C.; Ray, Paul S.; Gendreau, Keith C.; Chakrabarty, Deepto; Feroci, M.; Arzoumanian, Zaven; Brandt, S.; Hernanz, M.; Hui, C. M.; Jenke, P.; Maccarone, Thomas J.; Remillard, Ron; Wood, K. S.; Zane, S.

doi:10.1016/j.rinp.2017.09.013

Cited by 14 publications

(8 citation statements)

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“…An alternative technique is that of X-ray pulseprofile modelling (also known as light-curve or waveform modelling), which exploits (exterior) spacetime effects on rotationally pulsed emission from surface emission anisotropies (see, e.g., Watts et al 2016, for a general introduction to the technique). These X-ray techniques for estimating radii are being exploited by the recently-launched telescope NICER (Arzoumanian et al 2014), and would also be used by proposed large area X-ray telescope concepts such as STROBE-X (Wilson-Hodge et al 2017) and eXTP (Zhang et al 2016).…”

Section: Introductionmentioning

confidence: 99%

A pitfall of piecewise-polytropic equation of state inference

Raaijmakers

Riley

Watts

2018

Monthly Notices of the Royal Astronomical Society

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The only messenger radiation in the Universe which one can use to statistically probe the Equation of State (EOS) of cold dense matter is that originating from the nearfield vicinities of compact stars. Constraining gravitational masses and equatorial radii of rotating compact stars is a major goal for current and future telescope missions, with a primary purpose of constraining the EOS. From a Bayesian perspective it is necessary to carefully discuss prior definition; in this context a complicating issue is that in practice there exist pathologies in the general relativistic mapping between spaces of local (interior source matter) and global (exterior spacetime) parameters. In a companion paper, these issues were raised on a theoretical basis. In this study we reproduce a probability transformation procedure from the literature in order to map a joint posterior distribution of Schwarzschild gravitational masses and radii into a joint posterior distribution of EOS parameters. We demonstrate computationally that EOS parameter inferences are sensitive to the choice to define a prior on a joint space of these masses and radii, instead of on a joint space interior source matter parameters. We focus on the piecewise-polytropic EOS model, which is currently standard in the field of astrophysical dense matter study. We discuss the implications of this issue for the field.

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Section: Introductionmentioning

confidence: 99%

A pitfall of piecewise-polytropic equation of state inference

Raaijmakers

Riley

Watts

2018

Monthly Notices of the Royal Astronomical Society

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“…Constraining the dense matter EOS via astrophysical measurements of neutron stars is a major goal for current facilities: particularly for the X-ray telescope NICER (Arzoumanian et al 2014) and the gravitational wave telescopes LIGO and VIRGO (Abbott et al 2017). It is also a major science driver for the planned Square Kilometre Array radio telescope (Watts et al 2015) and proposals for the next generation of large-area X-ray timing telescopes (Watts et al 2016), such as the Enhanced X-ray Timing and Polarimetry mission (eXTP, Zhang et al 2016) and the NASA Probe Study STROBE-X (Wilson-Hodge et al 2017). The phenomena (to be) observed by these telescopes are distinct probes of the EOS.…”

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confidence: 99%

On parametrized cold dense matter equation-of-state inference

Riley

Raaijmakers

Watts

2018

Monthly Notices of the Royal Astronomical Society

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Constraining the equation of state of cold dense matter in compact stars is a major science goal for observing programmes being conducted using X-ray, radio, and gravitational wave telescopes. We discuss Bayesian hierarchical inference of parametrised dense matter equations of state. In particular we generalise and examine two inference paradigms from the literature: (i) direct posterior equation of state parameter estimation, conditioned on observations of a set of rotating compact stars; and (ii) indirect parameter estimation, via transformation of an intermediary joint posterior distribution of exterior spacetime parameters (such as gravitational masses and coordinate equatorial radii). We conclude that the former paradigm is not only tractable for large-scale analyses, but is principled and flexible from a Bayesian perspective whilst the latter paradigm is not. The thematic problem of Bayesian prior definition emerges as the crux of the difference between these paradigms. The second paradigm should in general only be considered as an ill-defined approach to the problem of utilising archival posterior constraints on exterior spacetime parameters; we advocate for an alternative approach whereby such information is repurposed as an approximative likelihood function. We also discuss why conditioning on a piecewise-polytropic equation of state model -currently standard in the field of dense matter study -can easily violate conditions required for transformation of a probability density distribution between spaces of exterior (spacetime) and interior (source matter) parameters.3 Note that, as stated above, one important caveat regards the assumption of BNS components sharing the same cold EOS -during inspiral -as stars which do not exist in compact relativistic binaries. In principle, if there is evidence that model complexity needs to be increased, these two classes of star could be assumed to only share a subset of (continuous, phenomenological) EOS parameters, whilst another subset of EOS parameters are used to emulate temperature dependence. 4 We use bold font to denote both a set of abstract parameters, and a point in the associated parameter space. For instance, θ ∈ T where T ⊂ R n , where the coordinates of point θ represent parameter values. 13 Or, interchangeably, a point in a space of parameters defined as random variables. 14 That is, all elements of X are ordered countably infinite tuples, but each coordinate is restricted to a compact subdomain of R, and a tuple of coordinates is a point in R ∞ .

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“…High-throughput X-ray spectroscopy: Future highthroughput X-ray spectroscopy missions such as the upcoming Advanced Telescope for High-ENergy Astrophysics (ATHENA) mission of the European Space Agency (anticipated launch: 2028) [129], the Spectroscopic Time-Resolving Observatory for Broadband Energy X-rays (STROBE-X) [195], or the Enhanced Timing and X-ray Polarimetry mission (eXTP) of the Chinese Academy of Sciences [199] can perform time resolved studies of the Fe Kα emission. As mentioned above, sensitive observations of frequency shifts (owing to gravitational and Doppler frequency shifts) as a function of the distance from the black hole (encoded in the orbital modulations of the signal) might be able to distinguish between Kerr and non-Kerr spacetimes (see also [26]).…”

Section: Discussionmentioning

confidence: 99%

Difficulties of quantitative tests of the Kerr-hypothesis with X-ray observations of mass accreting black holes

Krawczynski¹

2018

Gen Relativ Gravit

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X-ray studies of stellar mass black holes in X-ray binaries and mass-accreting supermassive black holes in Active Galactic Nuclei have achieved a high degree of maturity and have delivered detailed information about the astrophysical sources and the physics of black hole accretion. In this article, I review recent progress made towards using the X-ray observations for testing the "Kerr hypothesis" that the background spacetimes of all astrophysical quasi-stationary black holes are described by the Kerr metric. Although the observations have indeed revealed clear evidence for relativistic effects in strong-field gravity, quantitative tests of the Kerr hypothesis still struggle with theoretical and practical difficulties. In this article, I describe several recently introduced test metrics and review the status of constraining the background spacetimes of mass accreting stellar mass and supermassive black holes with these test metrics. The main conclusion of the discussion is that astrophysical uncertainties are large compared to the rather small observational differences between the Kerr and non-Kerr metrics precluding quantitative constraints on deviations from the Kerr metric at this point in time. I conclude with discussing future progress enabled by more detailed numerical simulations and by future X-ray spectroscopy, timing, polarimetry, and interferometry missions.

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STROBE-X: X-ray timing and spectroscopy on dynamical timescales from microseconds to years

Cited by 14 publications

References 10 publications

A pitfall of piecewise-polytropic equation of state inference

A pitfall of piecewise-polytropic equation of state inference

On parametrized cold dense matter equation-of-state inference

Difficulties of quantitative tests of the Kerr-hypothesis with X-ray observations of mass accreting black holes

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