77 research outputs found
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
Testing the Kerr metric with X-ray Reflection Spectroscopy of Mrk 335 Suzaku data
Einstein's gravity has undergone extensive tests in the weak field
gravitational limit, with results in agreement with theoretical predictions.
There exist theories beyond general relativity (GR) which modify gravity in the
strong field regime but agree with GR in the weak field. Astrophysical black
holes are believed to be described by the Kerr metric and serve as suitable
candidates to test strong gravity with electromagnetic radiation. We perform
such a test by fitting one Suzaku dataset of the narrow-line Seyfert 1 (NLS1)
galaxy Mrk 335 with X-ray reflection spectroscopy, using the Johannsen metric
to model the black hole spacetime and test for deviations from Kerr. We find
the data is best modeled with a hybrid model that includes both partial
covering absorption and a reflection component. This is the first time such a
model has been proposed for a high-flux (low reflection) Mrk 335 dataset. We
constrain the Johannsen deformation parameter to
, and the
parameter to , both at the 99%
confidence level. Although additional solutions at large deviations from the
Kerr metric show statistical similarity with the ones above, further analysis
suggests these solutions may be manifestations of uncertainties beyond our
control and do not represent the data. Hence, our results are in agreement with
the idea that the supermassive compact object at the center of Mrk 335 is
described by the Kerr metric.Comment: 13 pages, 9 figures. v2: refereed versio
Testing General Relativity with X-ray reflection spectroscopy: The Konoplya-Rezzolla-Zhidenko parametrization
X-ray reflection spectroscopy is a promising technique for testing general
relativity in the strong field regime, as it can be used to test the Kerr black
hole hypothesis. In this context, the parametrically deformed black hole
metrics proposed by Konoplya, Rezzolla \& Zhidenko (Phys. Rev. D93, 064015,
2016) form an important class of non-Kerr black holes. We implement this class
of black hole metrics in \textsc{relxill\_nk}, which is a framework we have
developed for testing for non-Kerr black holes using X-ray reflection
spectroscopy. We perform a qualitative analysis of the effect of the leading
order strong-field deformation parameters on typical observables like the
innermost stable circular orbits and the reflection spectra. We also present
the first X-ray constraints on some of the deformation parameters of this
metric, using \textit{Suzaku} data from the supermassive black hole in Ark~564,
and compare them with those obtained (or expected) from other observational
techniques like gravitational waves and black hole imaging.Comment: Minor updates. Published at Phys. Rev. D 102, 124071 (2020
Evolution of open clusters with or without black holes
Binary black holes (BHs) can be formed dynamically in the centers of star
clusters. The high natal kicks for stellar-mass BHs used in previous works made
it hard to retain BHs in star clusters. Recent studies of massive star
evolution and supernovae (SN) propose kick velocities that are lower due to the
fallback of the SN ejecta. We study the impact of these updates by performing
-body simulations following instantaneous gas expulsion. For comparison, we
simulate two additional model sets with the previous treatment of stars: one
with high kicks and another with artificial removal of the kicks. Our model
clusters initially consist of about one hundred thousand stars, formed with
centrally-peaked efficiency. We find that the updated treatment of stars, due
to the fallback-scaled lower natal kicks, allows clusters to retain SN remnants
after violent relaxation. The mass contribution of the retained remnants does
not exceed a few percent of the total bound cluster mass during the early
evolution. For this reason, the first giga year of evolution is not affected
significantly by this effect. Nevertheless, during the subsequent long-term
evolution, the retained BHs accelerate mass segregation, leading to the faster
dissolution of the clusters.Comment: 8 pages, 7 figures, submitted to MNRAS, comments are welcom
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