488 research outputs found
Design of a soft gamma-ray focusing telescope for the study of nuclear lines
We have studied the design of astronomical multilayer telescopes optimized for performance from 5 to 200 keV. This region of the spectrum contains important nuclear lines that are observable in supernovae and their remnants. The study of these lines can help to differentiate currently competing theories of supernova explosion. Our telescope design will enable us to measure the spectral lines of isotopes such as Ni-56 in Type Ia supernovae and Ti-44 in core-collapse remnants, as well as to observe active galactic nuclei at gamma-ray energies. We considered the performances of multilayers of various material pairs, including W/Si, Pt/C and Ni93V7/Si, as employed in conical-approximation Wolter I optics. We experimented with dividing the energy band of interest into several sections, and optimizing different groups of mirror shells within a single telescope for each smaller energy band. Different material pairs are also used for different energy bands, in order to obtain a higher overall performance. We also consider the significance of the energy bandwidth on the effectiveness of Joensen's parametrization of the multilayer thickness profile, and on the mirror performance within the band
Using Markov chain Monte Carlo methods for estimating parameters with gravitational radiation data
We present a Bayesian approach to the problem of determining parameters for
coalescing binary systems observed with laser interferometric detectors. By
applying a Markov Chain Monte Carlo (MCMC) algorithm, specifically the Gibbs
sampler, we demonstrate the potential that MCMC techniques may hold for the
computation of posterior distributions of parameters of the binary system that
created the gravity radiation signal. We describe the use of the Gibbs sampler
method, and present examples whereby signals are detected and analyzed from
within noisy data.Comment: 21 pages, 10 figure
Bayesian inference on compact binary inspiral gravitational radiation signals in interferometric data
Presented is a description of a Markov chain Monte Carlo (MCMC) parameter
estimation routine for use with interferometric gravitational radiational data
in searches for binary neutron star inspiral signals. Five parameters
associated with the inspiral can be estimated, and summary statistics are
produced. Advanced MCMC methods were implemented, including importance
resampling and prior distributions based on detection probability, in order to
increase the efficiency of the code. An example is presented from an
application using realistic, albeit fictitious, data.Comment: submitted to Classical and Quantum Gravity. 14 pages, 5 figure
The Broadband XMM-Newton and NuSTAR X-ray Spectra of Two Ultraluminous X-ray Sources in the Galaxy IC 342
We present results for two Ultraluminous X-ray Sources (ULXs), IC 342 X-1 and
IC 342 X-2, using two epochs of XMM-Newton and NuSTAR observations separated by
7 days. We observe little spectral or flux variability above 1 keV
between epochs, with unabsorbed 0.3--30 keV luminosities being
erg s for IC 342 X-1 and
erg s for IC 342 X-2, so that both were
observed in a similar, luminous state. Both sources have a high absorbing
column in excess of the Galactic value. Neither source has a spectrum
consistent with a black hole binary in low/hard state, and both ULXs exhibit
strong curvature in their broadband X-ray spectra. This curvature rules out
models that invoke a simple reflection-dominated spectrum with a broadened iron
line and no cutoff in the illuminating power-law continuum. X-ray spectrum of
IC 342 X-1 can be characterized by a soft disk-like black body component at low
energies and a cool, optically thick Comptonization continuum at high energies,
but unique physical interpretation of the spectral components remains
challenging. The broadband spectrum of IC 342 X-2 can be fit by either a hot
(3.8 keV) accretion disk, or a Comptonized continuum with no indication of a
seed photon population. Although the seed photon component may be masked by
soft excess emission unlikely to be associated with the binary system, combined
with the high absorption column, it is more plausible that the broadband X-ray
emission arises from a simple thin blackbody disk component. Secure
identification of the origin of the spectral components in these sources will
likely require broadband spectral variability studies.Comment: 12 pages, 11 figures, 5 Tables, Accepted for publication in The
Astrophysical Journa
A NuSTAR observation of the reflection spectrum of the low mass X-ray binary 4U 1728-34
We report on a simultaneous NuSTAR and Swift observation of the neutron star
low-mass X-ray binary 4U 1728-34. We identified and removed four Type I X-ray
bursts during the observation in order to study the persistent emission. The
continuum spectrum is hard and well described by a black body with 1.5
keV and a cutoff power law with 1.5 and a cutoff temperature of 25
keV. Residuals between 6 and 8 keV provide strong evidence of a broad Fe
K line. By modeling the spectrum with a relativistically blurred
reflection model, we find an upper limit for the inner disk radius of . Consequently we find that km,
assuming M=1.4{\mbox{\rm\,M_{\mathord\odot}}} and . We also find an
upper limit on the magnetic field of G.Comment: 9 pages, 8 figure
Coating of the HEFT telescope mirrors: method and results
We report on the coating of depth graded W/Si multilayers on the thermally slumped glass substrates for the HEFT flight telescopes. The coatings consists of several hundred bilayers in an optimized graded power law design with stringent requirements on uniformity and interfacial roughness. We present the details of the planar magnetron sputtering facility including the optimization of power, Ar pressure and collimating geometry which allows us to coat the several thousand mirror segments required for each telescope module on a time schedule consistent with the current HEFT balloon project as well as future hard X-ray satellite projects. Results are presented on the uniformity, interfacial roughness, and reflectivity and scatter at hard X-ray energies
<i>NuSTAR </i>Reveals Relativistic Reflection but no Ultra-fast Outflow in the Quasar PG1211+143
We report on four epochs of observations of the quasar PG 1211+143 using
NuSTAR. The net exposure time is 300 ks. Prior work on this source found
suggestive evidence of an 'ultra-fast outflow' (or, UFO) in the Fe K band, with
a velocity of approximately 0.1c. The putative flow would carry away a high
mass flux and kinetic power, with broad implications for feedback and black
hole-galaxy co-evolution. NuSTAR detects PG 1211+143 out to 30 keV, meaning
that the continuum is well-defined both through and above the Fe K band. A
characteristic relativistic disk reflection spectrum is clearly revealed, via a
broad Fe K emission line and Compton back-scattering curvature. The data offer
only weak constraints on the spin of the black hole. A careful search for UFO's
show no significant absorption feature above 90% confidence. The limits are
particularly tight when relativistic reflection is included. We discuss the
statistics and the implications of these results in terms of connections
between accretion onto quasars, Seyferts, and stellar-mass black holes, and
feedback into their host environments.Comment: Accepted in ApJ
The smooth cyclotron line in Her X-1 as seen with NuSTAR
Her X-1, one of the brightest and best studied X-ray binaries, shows a
cyclotron resonant scattering feature (CRSF) near 37 keV. This makes it an
ideal target for detailed study with the Nuclear Spectroscopic Telescope Array
(NuSTAR), taking advantage of its excellent hard X-ray spectral resolution. We
observed Her X-1 three times, coordinated with Suzaku, during one of the high
flux intervals of its 35d super-orbital period. This paper focuses on the shape
and evolution of the hard X-ray spectrum. The broad-band spectra can be fitted
with a powerlaw with a high-energy cutoff, an iron line, and a CRSF. We find
that the CRSF has a very smooth and symmetric shape, in all observations and at
all pulse-phases. We compare the residuals of a line with a Gaussian optical
depth profile to a Lorentzian optical depth profile and find no significant
differences, strongly constraining the very smooth shape of the line. Even
though the line energy changes dramatically with pulse phase, we find that its
smooth shape does not. Additionally, our data show that the continuum is only
changing marginally between the three observations. These changes can be
explained with varying amounts of Thomson scattering in the hot corona of the
accretion disk. The average, luminosity-corrected CRSF energy is lower than in
past observations and follows a secular decline. The excellent data quality of
NuSTAR provides the best constraint on the CRSF energy to date.Comment: 13 pages, 13 figures, accepted for publication in Ap
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