29 research outputs found
XMM-Newton observations of AM CVn binaries : V396 Hya and SDSS J1240–01
We present the results of XMM-Newton observations of two AM CVn systems - V396 Hya and SDSS J1240-01. Both systems are detected in X-rays and in the UV: neither shows coherent variability in their light curves. We compare the rms variability of the X-ray and UV power spectra of these sources with other AM CVn systems. Apart from ES Cet, AM CVn sources are not strongly variable in X-rays, while in the UV the degree of variability is related to the systems apparent brightness. The X-ray spectra of V396 Hya and SDSS J1240-01 show highly non-solar abundances, requiring enhanced nitrogen to obtain good fits. We compare the UV and X-ray luminosities for 7 AM CVn systems using recent distances. We find that the X-ray luminosity is not strongly dependent upon orbital period. However, the UV luminosity is highly correlated with orbital period with the UV luminosity decreasing with increasing orbital period. We expect that this is due to the accretion disk making an increasingly strong contribution to the UV emission at shorter periods. The implied luminosities are in remarkably good agreement with predictions
In-orbit performance of the EPIC-MOS detectors on XMM-Newton
XMM-Newton was launched into space on a highly eccentric 48 hour orbit on
December 10th 1999. XMM-Newton is now in its fifth year of operation and has
been an outstanding success, observing the Cosmos with imaging, spectroscopy
and timing capabilities in the X-ray and optical wavebands. The EPIC-MOS CCD
X-ray detectors comprise two out of three of the focal plane instruments on
XMM-Newton. In this paper we discuss key aspects of the current status and
performance history of the charge transfer ineffiency (CTI), energy resolution
and spectral redistribution function (rmf) of EPIC-MOS in its fifth year of
operation.Comment: 8 pages, 10 figures, SPIE Glasgow 21-25 June 2004, Session 548
The X-ray eclipse of the dwarf nova HT CAS observed by the XMM-Newton satellite: spectral and timing analysis
A cataclysmic variable is a binary system consisting of a white dwarf that
accretes material from a secondary object via the Roche-lobe mechanism. In the
case of long enough observation, a detailed temporal analysis can be performed,
allowing the physical properties of the binary system to be determined. We
present an XMM-Newton observation of the dwarf nova HT Cas acquired to resolve
the binary system eclipses and constrain the origin of the X-rays observed. We
also compare our results with previous ROSAT and ASCA data. After the spectral
analysis of the three EPIC camera signals, the observed X-ray light curve was
studied with well known techniques and the eclipse contact points obtained.
The X-ray spectrum can be described by thermal bremsstrahlung of temperature
keV plus a black-body component (upper limit) with
temperature eV. Neglecting the black-body, the bolometric
absorption corrected flux is erg
s cm, which, for a distance of HT Cas of 131 pc, corresponds to a
bolometric luminosity of erg s.
The study of the eclipse in the EPIC light curve permits us to constrain the
size and location of the X-ray emitting region, which turns out to be close to
the white dwarf radius. We measure an X-ray eclipse somewhat smaller (but only
at a level of ) than the corresponding optical one. If this
is the case, we have possibly identified the signature of either high latitude
emission or a layer of X-ray emitting material partially obscured by an
accretion disk.Comment: Accepted for publication on Astronomy and Astrophysics, 200
Status of the XMM-Newton cross-calibration with SASv6.5.0
Further achievements of the XMM-Newton cross-calibration - XMM internal as
well as with other X-ray missions - are presented. We explain the major changes
in the new version SASv6.5 of the XMM-Newton science analysis system. The
current status of the cross-calibration of the three EPIC cameras is shown.
Using a large sample of blazars, the pn energy redistribution at low energy
could be further calibrated, correcting the overestimation of fluxes in the
lowest energy regime. In the central CCDs of the MOSs, patches were identified
at the bore-sight positions, leading to an underestimation of the low energy
fluxes. The further improvement in the understanding of the cameras resulted in
a good agreement of the EPIC instruments down to lowest energies. The latest
release of the SAS software package already includes corrections for both
effects as shown in several examples of different types of sources. Finally the
XMM internal cross-calibration is completed by the presentation of the current
cross-calibration status between EPIC and RGS instruments. Major efforts have
been made in cross-calibrations with other X-ray missions, most importantly
with Chandra, of course, but also with currently observing satellites like
Swift.Comment: 6 pages, 23 figures. To appear in the proceedings of "The X-Ray
Universe 2005" conference, 2005 Sept 26-30, El Escorial, Madrid, Spai
Rank-(n – 1) convexity and quasiconvexity for divergence free fields
The CAST experiment at CERN (European Organization of Nuclear Research)
searches for axions from the sun. The axion is a pseudoscalar particle that was
motivated by theory thirty years ago, with the intention to solve the strong CP
problem. Together with the neutralino, the axion is one of the most promising
dark matter candidates. The CAST experiment has been taking data during the
last two years, setting an upper limit on the coupling of axions to photons
more restrictive than from any other solar axion search in the mass range below
0.1 eV. In 2005 CAST will enter a new experimental phase extending the
sensitivity of the experiment to higher axion masses. The CAST experiment
strongly profits from technology developed for high energy physics and for
X-ray astronomy: A superconducting prototype LHC magnet is used to convert
potential axions to detectable X-rays in the 1-10 keV range via the inverse
Primakoff effect. The most sensitive detector system of CAST is a spin-off from
space technology, a Wolter I type X-ray optics in combination with a prototype
pn-CCD developed for ESA's XMM-Newton mission. As in other rare event searches,
background suppression and a thorough shielding concept is essential to improve
the sensitivity of the experiment to the best possible. In this context CAST
offers the opportunity to study the background of pn-CCDs and its long term
behavior in a terrestrial environment with possible implications for future
space applications. We will present a systematic study of the detector
background of the pn-CCD of CAST based on the data acquired since 2002
including preliminary results of our background simulations.Comment: 11 pages, 8 figures, to appear in Proc. SPIE 5898, UV, X-Ray, and
Gamma-Ray Space Instrumentation for Astronomy XI
XMM-Newton X-ray and optical observations of the globular clusters M 55 and NGC 3201
We have observed two low concentration Galactic globular clusters with the
X-ray observatory XMM-Newton. We detect 47 faint X-ray sources in the direction
of M 55 and 62 in the field of view of NGC 3201. Using the statistical Log
N-Log S relationship of extragalactic sources derived from XMM-Newton Lockman
Hole observations, to estimate the background source population, we estimate
that very few of the sources (1.5+/-1.0) in the field of view of M 55 actually
belong to the cluster. These sources are located in the centre of the cluster
as we expect if the cluster has undergone mass segregation. NGC 3201 has
approximately 15 related sources, which are centrally located but are not
constrained to lie within the half mass radius. The sources belonging to this
cluster can lie up to 5 core radii from the centre of the cluster which could
imply that this cluster has been perturbed. Using X-ray (and optical, in the
case of M 55) colours, spectral and timing analysis (where possible) and
comparing these observations to previous X-ray observations, we find evidence
for sources in each cluster that could be cataclysmic variables, active
binaries, millisecond pulsars and possible evidence for a quiescent low mass
X-ray binary with a neutron star primary, even though we do not expect any such
objects in either of the clusters, due to their low central concentrations. The
majority of the other sources are background sources, such as AGN.Comment: 12 pages, 7 figures, accepted to be published in A&
X-ray source populations in the Galactic Plane
We present the first results from the \xmm Galactic Plane Survey (XGPS). In
the first phase of the programme, 22 pointings were used to cover a region of
approximately three square degrees between 19\deg -- 22\deg in Galactic
longitude and 0.6\deg in latitude. In total we have resolved over 400
point X-ray sources, at significance, down to a flux limit of
\ergseccm (2--10 keV). The combination of the XGPS
measurements in the hard X-ray band with the results from earlier surveys
carried out by \asca and \chan reveals the form of the low-latitude X-ray
source counts over 4 decades of flux. It appears that extragalactic sources
dominate below \ergseccm (2--10 keV), with a predominantly
Galactic source population present above this flux threshold. The nature of the
faint Galactic population observed by \xmm remains uncertain, although
cataclysmic variables and RS CVn systems may contribute substantially. \xmm
observes an enhanced surface brightness in the Galactic plane in the 2--6 keV
band associated with Galactic Ridge X-ray Emission (GRXE). The integrated
contribution of Galactic sources plus the breakthrough of extragalactic signal
accounts for up to 20 per cent of the observed surface brightness. The XGPS
results are consistent with the picture suggested from a deep \chan observation
in the Galactic plane, namely that the bulk of the GRXE is truly diffuse.Comment: 21 pages, 15 figures, accepted by MNRA
Pre-nova X-ray observations of V2491 Cyg (Nova Cyg 2008b)
Classical novae are phenomena caused by explosive hydrogen burning on an
accreting white dwarf. So far, only one classical nova has been identified in
X-rays before the actual optical outburst occurred (V2487 Oph). The recently
discovered nova, V2491 Cyg, is one of the fastest (He/N) novae observed so far.
Using archival ROSAT, XMM-Newton and Swift data, we show that V2491 Cyg was a
persistent X-ray source during its quiescent time before the optical outburst.
We present the X-ray spectral characteristics and derive X-ray fluxes. The
pre-outburst X-ray emission is variable, and at least in one observation it
shows a very soft X-ray source.Comment: 4 pages, 2 figures. Astronomy and Astrophysics, in pres
XMM-Newton observations of the Galactic globular clusters NGC 2808 and NGC 4372
Galactic globular clusters harbour binary systems that are detected as faint
X-ray sources. These close binaries are thought to play an important role in
the stability of the clusters by liberating energy and delaying the inevitable
core collapse of globular clusters. The inventory of close binaries and their
identification is therefore essential. We present XMM-Newton observations of
two Galactic globular clusters: NGC 2808 and NGC 4372. We use X-ray spectral
and variability analysis combined with ultra-violet observations made with the
XMM-Newton optical monitor and published data from the Hubble Space Telescope
to identify sources associated with the clusters. We compare the results of our
observations with estimates from population synthesis models. Five sources out
of 96 are likely to be related to NGC 2808. Nine sources are found in the field
of view of NGC 4372, none being located inside its half-mass radius. We find
one quiescent neutron star low mass X-ray binary candidate in the core of NGC
2808, and propose that the majority of the central sources in NGC 2808 are
cataclysmic variables. An estimation leads to ~20+/-10 cataclysmic variables
with luminosity above 4.25 x 10^31 erg s^-1. Millisecond pulsars could also be
present in the core of NGC 2808, and some sources outside of the half-mass
radius could possibly be linked to the cluster.Comment: 11 pages, 3 pages of online material, 10 figures and 9 tables.
Accepted for publication in A&
Polarimetry of binary systems: polars, magnetic CVs, XRBs
Polarimetry provides key physical information on the properties of
interacting binary systems, sometimes difficult to obtain by any other type of
observation. Indeed, radiation processes such as scattering by free electrons
in the hot plasma above accretion discs, cyclotron emission by mildly
relativistic electrons in the accretion shocks on the surface of highly
magnetic white dwarfs and the optically thin synchrotron emission from jets can
be observed. In this review, I will illustrate how optical/near-infrared
polarimetry allows one to estimate magnetic field strengths and map the
accretion zones in magnetic Cataclysmic Variables as well as determine the
location and nature of jets and ejection events in X-ray binaries.Comment: 26 pages, 16 figures; to be published in Astrophysics and Space
Science Library 460, Astronomical Polarisation from the Infrared to Gamma
Rays, Editors: Mignani, R., Shearer, A., S{\l}owikowska, A., Zane,