698 research outputs found
Science with the EXTraS Project: Exploring the X-ray Transient and variable Sky
The EXTraS project (Exploring the X-ray Transient and variable Sky) will
characterise the temporal behaviour of the largest ever sample of objects in
the soft X-ray range (0.1-12 keV) with a complex, systematic and consistent
analysis of all data collected by the European Photon Imaging Camera (EPIC)
instrument onboard the ESA XMM-Newton X-ray observatory since its launch. We
will search for, and characterize variability (both periodic and aperiodic) in
hundreds of thousands of sources spanning more than nine orders of magnitude in
time scale and six orders of magnitude in flux. We will also search for fast
transients, missed by standard image analysis. Our analysis will be completed
by multiwavelength characterization of new discoveries and phenomenological
classification of variable sources. All results and products will be made
available to the community in a public archive, serving as a reference for a
broad range of astrophysical investigations.Comment: 4 pages, 1 figure. Refereed Proceeding of "The Universe of Digital
Sky Surveys" conference held at the INAF - Observatory of Capodimonte,
Naples, on 25th-28th November 2014, to be published in the Astrophysics and
Space Science Proceedings, edited by Longo, Napolitano, Marconi, Paolillo,
Iodic
Imaging Molecules from Within: Ultra-fast, {\AA}ngstr\"om Scale Structure Determination of Molecules via Photoelectron Holography using Free Electron Lasers
A new scheme based on (i) upcoming brilliant X-ray Free Electron Laser (FEL)
sources, (ii) novel energy and angular dispersive, large-area electron imagers
and (iii) the well-known photoelectron holography is elaborated that provides
time-dependent three-dimensional structure determination of small to medium
sized molecules with {\AA}ngstr\"om spatial and femtosecond time resolution.
Inducing molecular dynamics, wave-packet motion, dissociation, passage through
conical intersections or isomerization by a pump pulse this motion is
visualized by the X-ray FEL probe pulse launching keV photoelectrons within few
femtoseconds from specific and well-defined sites, deep core levels of
individual atoms, inside the molecule. On their way out the photoelectrons are
diffracted generating a hologram on the detector that encodes the molecular
structure at the instant of photoionization, thus providing 'femtosecond
snapshot images of the molecule from within'. Detailed calculations in various
approximations of increasing sophistication are presented and three-dimensional
retrieval of the spatial structure of the molecule with {\AA}ngstr\"om spatial
resolution is demonstrated. Due to the large photo-absorption cross sections
the method extends X-ray diffraction based, time-dependent structure
investigations envisioned at FELs to new classes of samples that are not
accessible by any other method. Among them are dilute samples in the gas phase
such as aligned, oriented or conformer selected molecules, ultra-cold ensembles
and/or molecular or cluster objects containing mainly light atoms that do not
scatter X-rays efficiently.Comment: 18 pages, 11 figure
Background study for the pn-CCD detector of CERN Axion Solar Telescope
The CERN Axion Solar Telescope (CAST) experiment searches for axions from the
Sun converted into photons with energies up to around 10 keV via the inverse
Primakoff effect in the high magnetic field of a superconducting Large Hadron
Collider (LHC) prototype magnet. A backside illuminated pn-CCD detector in
conjunction with an X-ray mirror optics is one of the three detectors used in
CAST to register the expected photon signal. Since this signal is very rare and
different background components (environmental gamma radiation, cosmic rays,
intrinsic radioactive impurities in the set-up, ...) entangle it, a detailed
study of the detector background has been undertaken with the aim to understand
and further reduce the background level of the detector. The analysis is based
on measured data taken during the Phase I of CAST and on Monte Carlo
simulations of different background components. This study will show that the
observed background level (at a rate of (8.00+-0.07)10^-5 counts/cm^2/s/keV
between 1 and 7 keV) seems to be dominated by the external gamma background due
to usual activities at the experimental site, while radioactive impurities in
the detector itself and cosmic neutrons could make just smaller contribution.Comment: Comments: 10 pages, 9 figures and images, submitted to Astroparticle
Physic
Status of a DEPFET pixel system for the ILC vertex detector
We have developed a prototype system for the ILC vertex detector based on
DEPFET pixels. The system operates a 128x64 matrix (with ~35x25 square micron
large pixels) and uses two dedicated microchips, the SWITCHER II chip for
matrix steering and the CURO II chip for readout. The system development has
been driven by the final ILC requirements which above all demand a detector
thinned to 50 micron and a row wise read out with line rates of 20MHz and more.
The targeted noise performance for the DEPFET technology is in the range of
ENC=100 e-. The functionality of the system has been demonstrated using
different radioactive sources in an energy range from 6 to 40keV. In recent
test beam experiments using 6GeV electrons, a signal-to-noise ratio of S/N~120
has been achieved with present sensors being 450 micron thick. For improved
DEPFET systems using 50 micron thin sensors in future, a signal-to-noise of 40
is expected.Comment: Invited poster at the International Symposium on the Development of
Detectors for Particle, AstroParticle and Synchrotron Radiation Experiments,
Stanford CA (SNIC06) 6 pages, 12 eps figure
Discovery of narrow X-ray absorption features from the dipping low-mass X-ray binary X 1624-490 with XMM-Newton
We report the discovery of narrow X-ray absorption features from the dipping
low-mass X-ray binary X 1624-490 during an XMM-Newton observation in 2001
February. The features are identified with the K alpha absorption lines of Fe
xxv and Fe xxvi and have energies of 6.72 +/- 0.03 keV and 7.00 +/- 0.02 keV
and equivalent widths (EWs) of -7.5 +1.7 -6.3 eV and -16.6 +1.9 -5.9 eV,
respectively. The EWs show no obvious dependence on orbital phase, except
during a dip, and correspond to a column of greater than 10^17.3 Fe atom /cm2.
In addition, faint absorption features tentatively identified with Ni xxvii K
alpha and Fe xxvi K beta may be present. A broad emission feature at 6.58 +0.07
-0.04 keV with an EW of 78 +19 -6 eV is also evident. This is probably the 6.4
keV feature reported by earlier missions since fitting a single Gaussian to the
entire Fe-K region gives an energy of 6.39 +0.03 -0.04 keV. A deep absorption
feature is present during the dip with an energy consistent with Fe xxv K
alpha. This is the second dipping LMXRB source from which narrow Fe absorption
features have been observed. Until recently the only X-ray binaries known to
exhibit narrow X-ray absorption lines were two superluminal jet sources and it
had been suggested that these features are related to the jet formation
mechanism. It now appears likely that ionized absorption features may be common
characteristics of accreting systems with accretion disks.Comment: 6 pages. To appear in A&
Constraining the thermal history of the Warm-Hot Intergalactic Medium
We have identified a large-scale structure traced by galaxies at z=0.8,
within the Lockman Hole, by means of multi-object spectroscopic observations.
By using deep XMM images we have investigated the soft X-ray emission from the
Warm-Hot Intergalactic Medium (WHIM) expected to be associated with this
large-scale structure and we set a tight upper limit to its flux in the very
soft 0.2-0.4 keV band. The non-detection requires the WHIM at these redshifts
to be cooler than 0.1 keV. Combined with the WHIM emission detections at lower
redshift, our result indicates that the WHIM temperature is rapidly decreasing
with redshift, as expected in popular cosmological models.Comment: 10 pages, 5 figures, 1 appendix. A&A accepte
Quiet but still bright: XMM-Newton observations of the soft gamma-ray repeater SGR 0526-66
SGR 0526-66 was the first soft gamma-ray repeater (SGR) from which a giant
flare was detected in March 1979, suggesting the existence of magnetars, i.e.
neutron stars powered by the decay of their extremely strong magnetic field.
Since then, very little information has been obtained on this object, mainly
because it has been burst-inactive since 1983 and the study of its persistent
X-ray emission has been hampered by its large distance and its location in a
X-ray bright supernova remnant in the Large Magellanic Cloud. Here we report on
a comprehensive analysis of all the available XMM-Newton observations of SGR
0526-66. In particular, thanks to a deep observation taken in 2007, we measured
its pulsation period (P = 8.0544 +/- 0.0002 s) 6 years after its latest
detection by Chandra. This allowed us to detect for the first time a
significant reduction of its spin-down rate. From a comparison with two shorter
XMM-Newton observations performed in 2000 and 2001, we found no significant
changes in the spectrum, which is well modelled by an absorbed power-law with
nH = 4.6E+21 cm^-2 and photon index = 3.27. The high luminosity (about 4E+35
erg/s, in the 1-10 keV energy band) still observed about 25 years after the
latest detection of bursting activity places SGR 0526-66 in the group of bright
and persistent magnetar candidates.Comment: 5 pages, 3 figures (1 color) and 2 tables; Accepted for publication
in MNRAS Letter
Test Results on the Silicon Pixel Detector for the TTF-FEL Beam Trajectory Monitor
Test measurements on the silicon pixel detector for the beam trajectory
monitor at the free electron laser of the TESLA test facility are presented. To
determine the electronic noise of detector and read-out and to calibrate the
signal amplitude of different pixels the 6 keV photons of the manganese K line
are used. Two different methods determine the spatial accuracy of the detector:
In one setup a laser beam is focused to a straight line and moved across the
pixel structure. In the other the detector is scanned using a low-intensity
electron beam of an electron microscope. Both methods show that the symmetry
axis of the detector defines a straight line within 0.4 microns. The
sensitivity of the detector to low energy X-rays is measured using a vacuum
ultraviolet beam at the synchrotron light source HASYLAB. Additionally, the
electron microscope is used to study the radiation hardness of the detector.Comment: 14 pages (Latex), 13 figures (Postscript), submitted to Nuclear
Instruments and Methods
Variable iron-line emission near the black hole of Markarian 766
We investigate the link between ionised Fe X-ray line emission and continuum
emission in the bright nearby AGN, Mrk 766. A new long (433 ks) XMM-Newton
observation is analysed, together with archival data from 2000 and 2001. The
contribution from ionised line emission is measured and its time variations on
short (5-20 ks) timescales are correlated with the continuum emission. The
ionised line flux is found to be highly variable and to be strongly correlated
with the continuum flux, demonstrating an origin for the ionised line emission
that is co-located with the continuum emission. Most likely the emission is
ionised reflection from the accretion disc within a few A.U. of the central
black hole, and its detection marks the first time that such an origin has been
identified other than by fitting to spectral line profiles. Future observations
may be able to measure a time lag and hence achieve reverberation mapping of
AGN at X-ray energies.Comment: Accepted for publication, Astronomy and Astrophysics letter
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