2,687 research outputs found
The Composition of the Interstellar Medium towards the Lockman Hole. HI, UV and X-ray observations
The Lockman Hole is well known as the region with the lowest neutral atomic
hydrogen colum density on the entire sky. We present an analysis of the soft
X-ray background radiation towards the Lockman Hole using ROSAT all-sky survey
data. This data is correlated with the Leiden/Dwingeloo survey (Galactic HI
21cm-line emission) in order to model the soft X-ray background by using
radiative transfer calculations for four ROSAT energy bands simultaneously. It
turns out, that an important gas fraction, ranging between 20-50%,of the X-ray
absorbing material is not entirely traced by the HI but is in the form of
ionized hydrogen. Far-ultraviolet absorption line measurements by FUSE are
consistent with this finding and support an ionized hydrogen component towards
the Lockman Hole.Comment: 11 pages, 11 figures, Accepted for Publication in Astronomy &
Astrophysics, For full resolution images, see
http://www.astro.uni-bonn.de/~mkappes/pub/ms3506.pd
The harmonic power spectrum of the soft X-ray background I. The data analysis
Fluctuations of the soft X-ray background are investigated using harmonic
analysis. A section of the ROSAT All-Sky Survey around the north galactic pole
is used. The flux distribution is expanded into a set of harmonic functions and
the power spectrum is determined. Several subsamples of the RASS have been used
and the spectra for different regions and energies are presented. The effects
of the data binning in pixels are assessed and taken into account. The spectra
of the analyzed samples reflect both small scale effects generated by strong
discrete sources and the large scale gradients of the XRB distribution. Our
results show that the power spectrum technique can be effectively used to
investigate anisotropy of the XRB at various scales. This statistics will
become a useful tool in the investigation of various XRB components.Comment: 12 pages, A&A accepte
Missing baryons and the soft X-ray background
The X-ray background intensity around Lick count galaxies and rich clusters
of galaxies is investigated in three ROSAT energy bands. It is found that the
X-ray enhancements surrounding concentrations of galaxies exhibit significantly
softer spectrum than the standard cluster emission and the average
extragalactic background. The diffuse soft emission accompanying the galaxies
is consistent with the thermal emission of the hot gas postulated first by the
Cen & Ostriker hydrodynamic simulations. Our estimates of the gas temperature -
although subject to large uncertainties - averaged over several Mpc scales are
below 1 keV, which is substantially below the temperature of the intra-cluster
gas, but consistent with temperatures predicted for the local intergalactic
medium. It is pointed out that the planned ROSITA mission would be essential
for our understanding of the diffuse thermal component of the background.Comment: AA accepted, 6 pages, incl. 4 figure
The DRIFT Project: Searching for WIMPS with a Directional Detector
A low pressure time projection chamber for the detection of WIMPs is
discussed. Discrimination against Compton electron background in such a device
should be very good, and directional information about the recoil atoms would
be obtainable. If a full 3-D reconstruction of the recoil tracks can be
achieved, Monte Carlo studies indicate that a WIMP signal could be identified
with high confidence from as few as 30 detected WIMP-nucleus scattering events.Comment: 5 pages, 3 figures. Presented at Dark 98, Heidelberg, July 1998, and
to appear in conference proceeding
The XMM-Newton EPIC Background and the production of Background Blank Sky Event Files
We describe in detail the nature of XMM-Newton EPIC background and its
various complex components, summarising the new findings of the XMM-Newton EPIC
background working group, and provide XMM-Newton background blank sky event
files for use in the data analysis of diffuse and extended sources. Blank sky
event file data sets are produced from the stacking of data, taken from 189
observations resulting from the Second XMM-Newton Serendipitous Source
Catalogue (2XMMp) reprocessing. The data underwent several filtering steps,
using a revised and improved method over previous work, which we describe in
detail. We investigate several properties of the final blank sky data sets. The
user is directed to the location of the final data sets. There is a final data
set for each EPIC instrument-filter-mode combination.Comment: Paper accepted by A&A 22 December 2006. 14 pages, 8 figures. Paper
can also be found at http://www.star.le.ac.uk/~jac48/publications
Measuring Cluster Temperature Profiles with XMM/EPIC
Using the PV observation of A1795, we illustrate the capability of XMM-EPIC
to measure cluster temperature profiles, a key ingredient for the determination
of cluster mass profiles through the equation of hydrostatic equilibrium. We
develop a methodology for spatially resolved spectroscopy of extended sources,
adapted to XMM background and vignetting characteristics. The effect of the
particle induced background is discussed. A simple unbiased method is proposed
to correct for vignetting effects, in which every photon is weighted according
to its energy and location on the detector. We were able to derive the
temperature profile of A1795 up to 0.4 times the virial radius. A significant
and spatially resolved drop in temperature towards the center (r<200 kpc) is
observed, which corresponds to the cooling flow region of the cluster. Beyond
that region, the temperature is constant with no indication of a fall-off at
large radii out to 1.2 Mpc.Comment: 7 pages, 8 figures, Accepted for publication in A&A (special Letter
issue on XMM
XMM-Newton discovery of O VII emission from warm gas in clusters of galaxies
XMM-Newton recently discovered O VII line emission from ~2 million K gas near
the outer parts of several clusters of galaxies. This emission is attributed to
the Warm-Hot Intergalactic Medium. The original sample of clusters studied for
this purpose has been extended and two more clusters with a soft X-ray excess
have been found. We discuss the physical properties of the warm gas, in
particular the density, spatial extent, abundances and temperature.Comment: 8 pages, 3 figures, conference "Soft X-ray emission from clusters of
galaxies and related phenomena", ed. R. Lieu, Kluwer, in pres
Track Reconstruction and Performance of DRIFT Directional Dark Matter Detectors using Alpha Particles
First results are presented from an analysis of data from the DRIFT-IIa and
DRIFT-IIb directional dark matter detectors at Boulby Mine in which alpha
particle tracks were reconstructed and used to characterise detector
performance--an important step towards optimising directional technology. The
drift velocity in DRIFT-IIa was [59.3 +/- 0.2 (stat) +/- 7.5 (sys)] m/s based
on an analysis of naturally-occurring alpha-emitting background. The drift
velocity in DRIFT-IIb was [57 +/- 1 (stat) +/- 3 (sys)] m/s determined by the
analysis of alpha particle tracks from a Po-210 source. 3D range reconstruction
and energy spectra were used to identify alpha particles from the decay of
Rn-222, Po-218, Rn-220 and Po-216. This study found that (22 +/- 2)% of Po-218
progeny (from Rn-222 decay) are produced with no net charge in 40 Torr CS2. For
Po-216 progeny (from Rn-220 decay) the uncharged fraction is (100 +0 -35)%.Comment: 27 pages, 12 figures, 5 tables. Submitted to Nuclear Instruments and
Methods in Physics Research, Section A. Subj-class: Instrumentation and
Detector
The Supergiant Shell LMC2: II. Physical Properties of the 10^6 K Gas
LMC2 has the highest X-ray surface brightness of all know supergiant shells
in the Large Magellanic Cloud (LMC). The X-ray emission peaks within the
ionized filaments that define the shell boundary, but also extends beyond the
southern border of LMC2 as an X-ray bright spur. ROSAT HRI images reveal the
X-ray emission from LMC2 and the spur to be truly diffuse, indicating a hot
plasma origin. We have obtained ROSAT PSPC and ASCA SIS spectra to study the
physical conditions of the hot gas interior to LMC2 and the spur. Raymond-Smith
thermal plasma model fits to the X-ray spectra, constrained by HI 21-cm
emission-line measurements of the column density, show the plasma temperature
of the hot gas interior of LMC2 to be kT = 0.1 - 0.7 keV and of the spur to be
kT = 0.1 - 0.5 keV. We have compared the physical conditions of the hot gas
interior to LMC2 with those of other supergiant shells, superbubbles, and
supernova remnants (SNRs) in the LMC. We find that our derived electron
densities for the hot gas inside LMC2 is higher than the value determined for
the supergiant shell LMC4, comparable to the value determined for the
superbubble N11, and lower than the values determined for the superbubble N44
and a number of SNRs.Comment: 29 pages, 5 figures, to be published in Ap
First Results from the DRIFT-IIa Dark Matter Detector
Data from the DRIFT-IIa directional dark matter experiment are presented,
collected during a near continuous 6 month running period. A detailed
calibration analysis comparing data from gamma-ray, x-ray and neutron sources
to a GEANT4 Monte Carlo simulations reveals an efficiency for detection of
neutron induced recoils of 94+/-2(stat.)+/-5(sys.)%. Software-based cuts,
designed to remove non-nuclear recoil events, are shown to reject 60Co
gamma-rays with a rejection factor of better than 8x10-6 for all energies above
threshold. An unexpected event population has been discovered and is shown here
to be due to the alpha-decay of 222Rn daughter nuclei that have attached to the
central cathode. A limit on the flux of neutrons in the Boulby Underground
Laboratory is derived from analysis of unshielded and shielded data.Comment: 43 pages, 14 figures, submitted to Astroparticle Physic
- …