106 research outputs found
Blandford-Znajek mechanism in black holes in alternative theories of gravity
According to the Blandford-Znajek mechanism, black hole jets are powered by
the rotational energy of the compact object. In this work, we consider the
possibility that the metric around black holes may not be described by the Kerr
solution and we study how this changes the Blandford-Znajek model. If the
Blandford-Znajek mechanism is responsible for the formation of jets, the
estimate of the jet power in combination with another measurement can test the
nature of black hole candidates and constrain possible deviations from the Kerr
solution. However, this approach might become competitive with respect to other
techniques only when it will be possible to have measurements much more precise
than those available today.Comment: 12 pages, 5 figures. v2: refereed versio
GALLIFRAY -- A geometric modeling and parameter estimation framework for black hole images using bayesian techniques
Recent observations of the galactic centers of M87 and the Milky Way with the
Event Horizon Telescope have ushered in a new era of black hole based tests of
fundamental physics using very long baseline interferometry (VLBI). Being a
nascent field, there are several different modeling and analysis approaches in
vogue (e.g., geometric and physical models, visibility and closure amplitudes,
agnostic and multimessenger priors). We present \texttt{GALLIFRAY}, an
open-source Python-based framework for estimation/extraction of parameters
using VLBI data. It is developed with modularity, efficiency, and adaptability
as the primary objectives. This article outlines the design and usage of
\texttt{GALLIFRAY}. As an illustration, we fit a geometric and a physical model
to simulated datasets using markov chain monte carlo sampling and find good
convergence of the posterior distribution. We conclude with an outline of
further enhancements currently in development.Comment: 10 pages, 5 figures; accepted for publication in Ap
Testing general relativity with the reflection spectrum of the supermassive black hole in 1H0707495
Recently, we have extended the X-ray reflection model relxill to test the
spacetime metric in the strong gravitational field of astrophysical black
holes. In the present Letter, we employ this extended model to analyze
XMM-Newton, NuSTAR, and Swift data of the supermassive black hole in 1H0707-495
and test deviations from a Kerr metric parametrized by the Johannsen
deformation parameter . Our results are consistent with the
hypothesis that the spacetime metric around the black hole in 1H0707-495 is
described by the Kerr solution.Comment: 10 pages, 7 figures. v2: refereed versio
Public Release of RELXILL_NK: A Relativistic Reflection Model for Testing Einstein's Gravity
We present the public release version of relxill_nk, an X-ray reflection
model for testing the Kerr hypothesis and general relativity. This model
extends the relxill model that assumes the black hole spacetime is described by
the Kerr metric. We also present relxilllp_nk, the first non-Kerr X-ray
reflection model with a lamppost corona configuration, as well as all other
models available in the full relxill_nk package. In all models the relevant
relativistic effects are calculated through a general relativistic ray-tracing
code that can be applied to any well-behaved, stationary, axisymmetric, and
asymptotically flat black hole spacetime. We show that the numerical error
introduced by using a ray-tracing code is not significant as compared with the
observational error present in current X-ray reflection spectrum observations.
In addition, we present the reflection spectrum for the Johannsen metric as
calculated by relxill_nk.Comment: 15 pages, 8 figures. v2: refereed version. Code and documentation
available at
http://www.physics.fudan.edu.cn/tps/people/bambi/Site/RELXILL_NK.html and at
http://www.tat.physik.uni-tuebingen.de/~nampalliwar/relxill_nk
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