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