18 research outputs found
Using the X-ray Emission Lines of Seyfert 2 AGN to Measure Abundance Ratios
We measure the metal abundance ratios in the X-ray photoionized gas located
near the narrow line region of a sample of Seyfert 2 AGN. The high-resolution
X-ray spectra observed with the Chandra high- and low-energy transmission
grating spectrometers are compared with models of the resonant scattering and
recombination emission from a plasma in thermal balance, and with multiple
temperature zones. The abundance ratios in the sample are close to the Solar
values, with slight over-abundances of N in NGC 1068, and of Ne in NGC 4151.
Our X-ray spectral models use fewer degrees of freedom than previous works.Comment: 2 pages, 1 figure, to appear in the proceedings of the conference
"Multiwavelenth AGN Surveys", held in Cozumel, Mexico, December 200
Atomic X-Ray Spectra of Accretion Disk Atmospheres in the Kerr Metric
We calculate the atmospheric structure of an accretion disk around a Kerr
black hole and obtain its X-ray spectrum, which exhibits prominent atomic
transitions under certain circumstances. The gravitational and Doppler
(red)shifts of the C V, C VI, O VII, O VIII, and Fe I-XXVI emission lines are
observable in active galaxies. We quantify the line emissivities as a function
of radius, to identify the effects of atmospheric structure, and to determine
the usefulness of these lines for probing the disk energetics. The line
emissivities do not always scale linearly with the incident radiative energy,
as in the case of Fe XXV and Fe XXVI. Our model incorporates photoionization
and thermal balance for the plasma, the hydrostatic approximation perpendicular
to the plane of the disk, and general relativistic tidal forces. We include
radiative recombination rates, fluorescence yields, Compton scattering, and
photoelectric opacities for the most abundant elements.Comment: 4 pages, 1 figure, to appear in the Proc. of the 10th Marcel
Grossmann Meeting on General Relativity, World Scientific, Rio de Janeiro,
July 20-26, 200
Reprocessing of Soft X-ray Emission Lines in Black Hole Accretion Disks
By means of a Monte Carlo code that accounts for Compton scattering and
photoabsorption followed by recombination, we have investigated the radiation
transfer of Ly alpha, He alpha, and recombination continua photons of H- and
He-like C, N, O, and Ne produced in the photoionized atmosphere of a
relativistic black hole accretion disk. We find that photoelectric opacity
causes significant attenuation of photons with energies above the O VIII
K-edge; that the conversion efficiencies of these photons into lower-energy
lines and recombination continua are high; and that accounting for this
reprocessing significantly (by factors of 21% to 105%) increases the flux of
the Ly alpha and He alpha emission lines of H- and He-like C and O escaping the
disk atmosphere.Comment: 4 pages including 4 encapsulated postscript figures; LaTeX format,
uses aastex.cls and emulateapj5.sty; accepted on 2004 January 13 for
publication in The Astrophysical Journa
Development of thermally formed glass optics for astronomical hard x-ray telescopes
The next major observational advance in hard X-ray/soft gamma-ray astrophysics will come with the implementation of telescopes capable of focusing 10-200 keV radiation. Focusing allows high signal-to-noise imaging and spectroscopic observations of many sources in this band for the first time. The recent development of depth-graded multilayer coatings has made the design of telescopes for this bandpass practical, however the ability to manufacture inexpensive substrates with appropriate surface quality and figure to achieve sub-arcminute performance has remained an elusive goal. In this paper, we report on new, thermally-formed glass micro-sheet optics capable of meeting the requirements of the next-generation of astronomical hard X-ray telescopes
XMM-Newton EPIC & OM observations of Her X-1 over the 35 day beat period
We present the results of a series of XMM-Newton EPIC and OM observations of
Her X-1, spread over a wide range of the 35 day precession period. We confirm
that the spin modulation of the neutron star is weak or absent in the low state
- in marked contrast to the main or short-on states. During the states of
higher intensity, we observe a substructure in the broad soft X-ray modulation
below ~1keV, revealing the presence of separate peaks which reflect the
structure seen at higher energies. The strong fluorescence emission line at
~6.4keV is detected in all observations (apart from one taken in the middle of
eclipse), with higher line energy, width and normalisation during the main-on
state. In addition, we report the detection of a second line near 7keV in 10 of
the 15 observations taken during the low-intensity states of the system. This
feature is rather weak and not significantly detected during the main-on state,
when the strong continuum emission dominates the X-ray spectrum. Spin resolved
spectroscopy just after the rise to the main-on state shows that the variation
of the Fe Kalpha line at 6.4 keV is correlated with the soft X-ray emission.
This confirms our past finding based on the XMM-Newton observations made
further into the main-on state, and indicates the common origin for the thermal
component and the Fe Kalpha line detected at these phases. We also find that
the normalisation of the 6.4keV line during the low state is correlated with
the binary orbital phase, having a broad maximum centered near phi_(orbit) ~
0.5. We discuss these observations in the context of previous observations,
investigate the origin of the soft and hard X-rays and consider the emission
site of the 6.4keV and 7keV emission lines.Comment: 12 pages, accepted MNRA
Hard x-ray characterization of a HEFT single-reflection prototype
We have measured the hard X-ray reflectivity and imaging performance from depth graded W/Si multilayer coated mirror segments mounted in a single reflection cylindrical prototype for the hard X-ray telescopes to be flown on the High Energy Focusing Telescope (HEFT) balloon mission. Data have been obtained in the energy range from 18 - 170 keV at the European Synchrotron Radiation Facility and at the Danish Space Research Institute at 8 keV. The modeling of the reflectivity data demonstrate that the multilayer structure can be well described by the intended power law distribution of the bilayer thicknesses optimized for the telescope performance and we find that all the data is consistent with an interfacial width of 4.5 Ă
. We have also demonstrated that the required 5% uniformity of the coatings is obtained over the mirror surface and we have shown that it is feasible to use similar W/Si coatings for much higher energies than the nominal energy range of HEFT leading the way for designing Gamma-ray telescopes for future astronomical applications. Finally we have demonstrate 35 arcsecond Half Power Diameter imaging performance of the one bounce prototype throughout the energy range of the HEFT telescopes
Hard x-ray optics for the HEFT balloon-borne payload: prototype design and status
We report on the current status and performance of prototype hard x-ray optics we are producing for use on the high energy focusing telescope (HEFT) experiment. The baseline substrates are thermally formed glass mirrors that are overcoated with multilayers to provide good performance throughout the 20-80 keV bandpass. Progress made in the thermal forming process as well as in the multilayer performance has allowed production of optics that meet or exceed all HEFT requirements. We present metrology on the substrates and result from x-ray characterization. A novel mounting scheme for the individual telescope shells is currently being tested. If successful the mounting technique will produce a monolithic, extremely stiff and robust optic
X-ray scatter measurements from thermally slumped thin glass substrates for the HEFT hard x-ray telescopes
We have performed x-ray specular reflectivity and scattering measurements of thermally slumped glass substrates on x-ray diffractometers utilizing a rotating anode x-ray source at the Danish Space Research Institute (DSRI) and synchrotron radiation at the European Synchrotron Radiation Facility (ESRF) optics Bending Magnet beamline. In addition, we tested depth graded W/Si multilayer-coated slumped glass using x-ray specular reflectivity measurements at 8.048 keV and 28 keV and energy-dispersive measurements in the 20-50 keV rang at a double-axis diffractometer at the Orsted Laboratory, University of Copenhagen. The thermally slumped glass substrates will be used to fabricate the hard x-ray grazing incidence optics for the High-Energy Focusing Telescope. We compared the measurements to the SODART- mirrors from the SRG telescope mission program. The surface scatter measurement of the thermally slumped glass substrates yields Half Power Diameters (HPD's) of single- bounce mirrors of full-illuminated lengths of ~ 40 arcseconds for typical substrates and as low as ~ 10 arcseconds for the best substrates, whereas the SODART mirrors yields HPD's of ~ 80 arcseconds with very little variation. Both free-standing glass substrates and prototype mounted and multilayer-coated optics were tested. The result demonstrate that the surface scatter contribution, plus any contribution from the mounting procedure, to the Half Power Diameter from a telescope using the slumped glass optics will be in the subarcminute range.In addition we measured low surface microroughness, yielding high reflectivity, from the glass substrates, as well as from the depth graded W/Si multilayer-coated glass glass (interfacial width 4.2 Ă
)
Hard x-ray characterization of a HEFT single-reflection prototype
We have measured the hard X-ray reflectivity and imaging performance from depth graded W/Si multilayer coated mirror segments mounted in a single reflection cylindrical prototype for the hard X-ray telescopes to be flown on the High Energy Focusing Telescope (HEFT) balloon mission. Data have been obtained in the energy range from 18 - 170 keV at the European Synchrotron Radiation Facility and at the Danish Space Research Institute at 8 keV. The modeling of the reflectivity data demonstrate that the multilayer structure can be well described by the intended power law distribution of the bilayer thicknesses optimized for the telescope performance and we find that all the data is consistent with an interfacial width of 4.5 Ă
. We have also demonstrated that the required 5% uniformity of the coatings is obtained over the mirror surface and we have shown that it is feasible to use similar W/Si coatings for much higher energies than the nominal energy range of HEFT leading the way for designing Gamma-ray telescopes for future astronomical applications. Finally we have demonstrate 35 arcsecond Half Power Diameter imaging performance of the one bounce prototype throughout the energy range of the HEFT telescopes