1,097 research outputs found
Testing the performance and accuracy of the RELXILL model for the relativistic X-ray reflection from accretion disks
The reflection spectroscopic model RELXILL is commonly implemented in
studying relativistic X-ray reflection from accretion disks around black holes.
We present a systematic study of the model's capability to constrain the
dimensionless spin and ionization parameters from 6,000 NuSTAR
simulations of a bright X-ray source employing the lamppost geometry. We employ
high count spectra to show the limitations in the model without being confused
with limitations in signal-to-noise. We find that both parameters are
well-recovered at 90% confidence with improving constraints at higher
reflection fraction, high spin, and low source height. We test spectra across a
broad range - first at 1010 and then 10 total source counts
across the effective 3-79 keV band of NuSTAR, and discover a strong dependence
of the results on how fits are performed around the starting parameters, owing
to the complexity of the model itself. A blind fit chosen over an approach that
carries some estimates of the actual parameter values can lead to significantly
worse recovery of model parameters. We further stress on the importance to span
the space of nonlinear-behaving parameters like carefully and
thoroughly for the model to avoid misleading results. In light of selecting
fitting procedures, we recall the necessity to pay attention to the choice of
data binning and fit statistics used to test the goodness of fit by
demonstrating the effect on the photon index . We re-emphasize and
implore the need to account for the detector resolution while binning X-ray
data and using Poisson fit statistics instead while analyzing Poissonian data.Comment: 9 pages, 6 figures, accepted for publication in Ap
Testing the Kerr nature of black hole candidates using iron line reverberation mapping in the Cardoso-Pani-Rico framework
The iron Kα line commonly observed in the x-ray spectrum of black hole candidates is produced by x-ray fluorescence of the inner accretion disk. This line can potentially be quite a powerful tool to probe the spacetime geometry around these objects and test the Kerr black hole hypothesis. In a previous paper, we studied the ability to constrain possible deviations from the Kerr solution from the standard time-integrated iron line spectrum within the Cardoso-Pani-Rico framework. In the present work, we expand on that study and consider iron line reverberation mapping in the Cardoso-Pani-Rico framework. That is, we consider the time evolution of the iron line profile in response to fluctuations in the x-ray primary source. Our simulations clearly show that the time informatio n in reverberation mapping can better constrain the background metric than the time-integrated approach, and this is true, notably, for the deformation parameter ϵ[subscript 3][superscript r], which is only weakly informed by a time-integrated observation.United States. National Aeronautics and Space Administration (Grant PF5-160144
On Estimating the High-Energy Cutoff in the X-ray Spectra of Black Holes via Reflection Spectroscopy
The fundamental parameters describing the coronal spectrum of an accreting
black hole are the slope of the power-law continuum and the energy
at which it rolls over. Remarkably, this parameter can be accurately
measured for values as high as 1 MeV by modeling the spectrum of X-rays
reflected from a black hole accretion disk at energies below 100 keV. This is
possible because the details in the reflection spectrum, rich in fluorescent
lines and other atomic features, are very sensitive to the spectral shape of
the hardest coronal radiation illuminating the disk. We show that fitting
simultaneous NuSTAR (3-79 keV) and low-energy (e.g., Suzaku) data with the most
recent version of our reflection model RELXILL, one can obtain reasonable
constraints on at energies from tens of keV up to 1 MeV, for a source
as faint as 1 mCrab in a 100 ks observation.Comment: Accepted for publication in ApJL, 6 pages, 5 figure
X-ray Reflection Spectroscopy of the Black Hole GX 339-4: Exploring the Hard State with Unprecedented Sensitivity
We analyze {\it simultaneously} six composite {\it RXTE} spectra of GX 339--4
in the hard state comprising 77 million counts collected over 196 ks. The
source spectra are ordered by luminosity and spanthe range 1.6\% to 17\% of the
Eddington luminosity. Crucially, using our new tool {\tt pcacorr}, we
re-calibrate the data to a precision of 0.1\%, an order of magnitude
improvement over all earlier work. Using our advanced reflection model {\tt
relxill}, we target the strong features in the component of emission reflected
from the disk, namely, the relativistically-broadened Fe K emission line, the
Fe K edge and the Compton hump. We report results for two joint fits to the six
spectra: For the first fit, we fix the spin parameter to its maximal value
() and allow the inner disk radius to vary. Results
include (i) precise measurements of , with evidence that the disk
becomes slightly truncated at a few percent of Eddington; and (ii) an
order-of-magnitude swing with luminosity in the high energy cutoff, which
reaches keV at our lowest luminosity. For the second fit, we make the
standard assumption in estimating spin that the inner edge of the accretion
disk is located at the innermost stable circular orbit () and find (90\% confidence,
statistical). For both fits, and at the same level of statistical confidence,
we estimate that the disk inclination is deg and that the Fe
abundance is super-solar, .Comment: Accepted for publication in ApJ, 20 pages, 13 figure
The Mediating Role Of EMS Teamwork As It Pertains To HR Factors And Perceived Environmental Performance
Little management theory or empirical results exist to guide managers in maximizing employee efforts to successfully implement Environmental Management Systems (EMS). In response, this study examines the relationship among Human Resource (HR) factors and employee perceptions of environmental performance. Four hundred thirty-seven (437) employees were surveyed in an organization with a well-developed EMS program and ISO 14001 certification. Results suggest that management support for EMS, EMS training, employee empowerment, and EMS rewards are related to perceived environmental performance. Furthermore, EMS teamwork plays a mediating role between some of independent variables and perceived environmental performance. Finally, implications for managers are discussed
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