76 research outputs found
Toward volume manufacturing of high-performance soft x-ray critical-angle transmission gratings
High-resolution () x-ray absorption and
emission line spectroscopy in the soft x-ray band is a crucial diagnostic for
the exploration of the properties of ubiquitous warm and hot plasmas and their
dynamics in the cosmic web, galaxy clusters, galaxy halos, intragalactic space,
and star atmospheres. Soft x-ray grating spectroscopy with has
been demonstrated with critical-angle transmission (CAT) gratings. CAT gratings
combine the relaxed alignment and temperature tolerances and low mass of
transmission gratings with high diffraction efficiency blazed in high orders.
They are an enabling technology for the proposed Arcus grating explorer and
were selected for the Lynx design reference mission grating spectrometer
instrument. Both Arcus and Lynx require the manufacture of hundreds to perhaps
large-area CAT gratings. We are developing new patterning and
fabrication process sequences that are conducive to large-format volume
processing on state-of-the-art 200 mm wafer tools. Recent x-ray tests on 200
nm-period gratings patterned using e-beam-written masks and 4x projection
lithography in conjunction with silicon pore focusing optics demonstrated at 1.49 keV. Extending the grating depth from 4 m to 6
m is predicted to lead to significant improvements in diffraction
efficiency and is part of our current efforts using a combination of deep
reactive-ion etching and wet etching in KOH solution. We describe our recent
progress in grating fabrication and report our latest diffraction efficiency
and modeling results.Comment: 11 pages, 8 figures, submitted to Proc. SPIE 1144
Discovery and identification of infrared counterpart candidates of four Galactic centre low mass X-ray binaries
The near infrared (nIR)/optical counterparts of low mass X-ray binaries
(LMXBs) are often observationally dim and reside in high source density fields
which make their identification problematic; however, without such a
counterpart identification we are unable to investigate many of the properties
of LMXB systems. Here, in the context of a larger identification campaign, we
examine the fields of four LMXB systems near the Galactic centre, in a bid to
identify nIR/optical counterparts to the previously detected X-ray point
sources. We obtain nIR/optical images of the fields with the ESO - New
Technology Telescope and apply standard photometric and astrometric
calibrations; these data are supplemented by Spitzer-GLIMPSE catalog data. On
the basis of positional coincidence with the arcsecond accurate X-ray
positions, we identify unambiguous counterpart candidates for XTE J1637-498,
IGR J17379-3747, IGR J17585-3057 and GX 9+1. We propose tentative nIR
counterparts of four LMXBs which require further investigation to confirm their
associations to the X-ray sources.Comment: Accepted to A&A (5 pages, 4 figures
BeppoSAX observation of 4U\u20091705-44: detection of hard X-ray emission in the soft state
Context. 4U 1705-44 is one of the best-studied type I X-ray burster and atoll sources.
Aims. Since it covers a wide range in luminosity (from a few to 50 x 10(36) erg s(-1)) and shows clear spectral state transitions, it represents a good laboratory for testing the accretion models proposed for atoll sources.
Methods. We analyzed the energy spectrum accumulated with BeppoSAX observations (43.5 ks) in August 2000 when the source was in a soft spectral state.
Results. The continuum of the wide-band energy spectrum is well-described by the sum of a blackbody (kT(bb) similar to 0.56 keV) and a Comptonized component (seed-photon temperature kT(W) similar to 1 keV, electron temperature kT(e) similar to 2.7 keV, and optical depth tau similar to 11). A hard tail was detected at energies above similar to 25 keV. The latter can be modeled by a power law having a photon index similar to 2.9, which contributes similar to 11% of the total flux in the range 0.1-200 keV. A broad emission line, possibly from a relativistic accretion disk, models the feature in the Fe K line region of the spectrum.
Conclusions. This is the first time that a high-energy tail has been observed during a soft state of the source
The Discovery of a State Dependent Hard Tail in the X-ray Spectrum of the Luminous Z-source GX 17+2
We report results of a BeppoSAX (0.1-200 keV) observation of the Z-type low
mass X-ray binary GX 17+2. The source was on the so-called Horizontal and
Normal branches. Energy spectra were selected based on the source position in
the X-ray hardness-intensity diagram. The continuum could be fairly well
described by the sum of a ~0.6 keV blackbody, contributing ~10% of the observed
0.1-200 keV flux, and a Comptonized component, resulting from upscattering of
\~1 keV seed photons by an electron cloud with temperature of ~3 keV and
optical depth of ~10. Iron K-line and edge were also present at energies 6.7
and 8.5 keV, respectively. In the spectra of the Horizontal branch a hard tail
was clearly detected at energies above ~30 keV. It could be fit by a power law
of photon index ~2.7, contributing ~8% of the source flux. This component
gradually faded as the source moved towards the Normal branch, where it was no
longer detectable. We discuss the possible origin of this component and the
similarities with the spectra of Atoll sources and black hole X-ray binaries.Comment: 11 pages, including 2 figures. Accepted for publication in ApJ
Letter
Discovery of X-ray burst triplets in EXO 0748-676
[Abridged] Type-I X-ray bursts are thermonuclear flashes that take place on
the surface of accreting neutron stars. The wait time between consecutive
bursts is set by the time required to accumulate the fuel needed to trigger a
new burst; this is at least one hour. Sometimes secondary bursts are observed,
approximately 10 min after the main burst. These short wait-time bursts are not
yet understood. We observed the low-mass X-ray binary and X-ray burster EXO
0748-676 with XMM-Newton for 158 h, during 7 uninterrupted observations lasting
up to 30 h each. We detect 76 X-ray bursts. Most remarkably, 15 of these bursts
occur in burst triplets, with wait times of 12 min between the three components
of the triplet. We also detect 14 doublets with similar wait times between the
two components of the doublet. The characteristics of the bursts indicate that
possibly all bursts in this system are hydrogen-ignited, in contrast with most
other frequent X-ray bursters in which bursts are helium-ignited, but
consistent with the low mass accretion rate in EXO 0748-676. Possibly the
hydrogen ignition is the determining factor for the occurrence of short
wait-time bursts.Comment: 23 pages, 16 figures, accepted for publication in A&
Optical design and performance simulations for the 1.49 keV beamline of the BEaTriX X-ray facility
The BEaTriX (Beam Expander Testing X-ray) facility, now operational at INAF-Brera Astronomical Observatory, will represent a cornerstone in the acceptance roadmap of Silicon Pore Optics (SPO) mirror modules, and will so contribute to the final angular resolution of the ATHENA X-ray telescope. By expansion and collimation of a microfocus X-ray source via a paraboloidal mirror, a monochromation stage, and an asymmetric crystal, BEaTriX enables the full-aperture illumination of an SPO mirror module with a parallel, monochromatic, and broad (140 mm × 60 mm) X-ray beam. The beam then propagates in a 12 m vacuum range to image the point spread function of the mirror module, directly on a focal plane camera. Currently the 4.51 keV beamline, based on silicon crystals, is operational in BEaTriX. A second beamline at 1.49 keV, which requires a separate paraboloidal mirror and organic crystals (ADP) for beam expansion, is being realized. As for monochromators, the current design is based on asymmetric quartz crystals. In this paper, we show the current optical design of the 1.49 keV beamline and the optical simulations carried out to predict the achievable performances in terms of beam collimation, intensity, and uniformity. In the next future, the simulation activity will allow us to determine manufacturing and alignment tolerances for the optical components
X-ray tests of the ATHENA mirror modules in BEaTriX: from design to reality
The BEaTriX (Beam Expander Testing X-ray) facility is now operative at the INAF-Osservatorio Astronomico Brera (Merate, Italy). This facility has been specifically designed and built for the X-ray acceptance tests (PSF and Effective Area) of the ATHENA Silicon Pore Optics (SPO) Mirror Modules (MM). The unique setup creates a parallel, monochromatic, large X-ray beam, that fully illuminates the aperture of the MMs, generating an image at the ATHENA focal length of 12 m. This is made possible by a microfocus X-ray source followed by a chain of optical components (a paraboloidal mirror, 2 channel cut monochromators, and an asymmetric silicon crystal) able to expand the X-ray beam to a 6 cm × 17 cm size with a residual divergence of 1.5 arcsec (vertical) × 2.5 arcsec (horizontal). This paper reports the commissioning of the 4.5 keV beam line, and the first light obtained with a Mirror Module
First light of BEaTriX, the new testing facility for the modular X-ray optics of the ATHENA mission
Aims: The Beam Expander Testing X-ray facility (BEaTriX) is a unique X-ray apparatus now operated at the Istituto Nazionale di Astrofisica (INAF), Osservatorio Astronomico di Brera (OAB), in Merate, Italy. It has been specifically designed to measure the point spread function (PSF) and the effective area (EA) of the X-ray mirror modules (MMs) of the Advanced Telescope for High-ENergy Astrophysics (ATHENA), based on silicon pore optics (SPO) technology, for verification before integration into the mirror assembly. To this end, BEaTriX generates a broad, uniform, monochromatic, and collimated X-ray beam at 4.51 keV. The beam collimation is better than a few arcseconds, ensuring reliable tests of the ATHENA MMs, in their focus at a 12 m distance. Methods: In BEaTriX, a micro-focus X-ray source with a titanium anode is placed in the focus of a paraboloidal mirror, which generates a parallel beam. A crystal monochromator selects the 4.51 keV line, which is expanded to the final size by a crystal asymmetrically cut with respect to the crystalline planes. An in-house-built Hartmann plate was used to characterize the X-ray beam divergence, observing the deviation of X-ray beams from the nominal positions, on a 12-m-distant CCD camera. After characterization, the BEaTriX beam has the nominal dimensions of 170 mm × 60 mm, with a vertical divergence of 1.65 arcsec and a horizontal divergence varying between 2.7 and 3.45 arcsec, depending on the monochromator setting: either high collimation or high intensity. The flux per area unit varies from 10 to 50 photons/s/cm2 from one configuration to the other. Results: The BEaTriX beam performance was tested using an SPO MM, whose entrance pupil was fully illuminated by the expanded beam, and its focus was directly imaged onto the camera. The first light test returned a PSF and an EA in full agreement with expectations. As of today, the 4.51 keV beamline of BEaTriX is operational and can characterize modular X-ray optics, measuring their PSF and EA with a typical exposure of 30 min. Another beamline at 1.49 keV is under development and will be integrated into the current equipment. We expect BEaTriX to be a crucial facility for the functional test of modular X-ray optics, such as the SPO MMs for ATHENA
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