93 research outputs found
The Galactic plane at faint X-ray fluxes - II. Stacked X-ray spectra of a sample of serendipitous XMM-Newton sources
We have investigated the X-ray spectral properties of a sample of 138 X-ray
sources detected serendipitously in observations of the Galactic
plane, at an intermediate to faint flux level. We divide our sample into 5
subgroups according to the spectral hardness of the sources, and stack (i.e.
co-add) the individual source spectra within each subgroup. As expected these
stacked spectra show a softening trend from the hardest to the softest
subgroups, which is reflected in the inferred line-of-sight column density. The
spectra of the three hardest subgroups are characterized by a hard continuum
plus superimpose Fe-line emission in the 6--7 keV bandpass. The average
equivalent width (EW) of the 6.7-keV He-like Fe-K line is
170 eV, whereas the 6.4-keV Fe-K fluorescence line from neutral
iron and the 6.9-keV H-like Fe-Ly line have EWs of 89 eV
and 81 eV respectively, i.e. roughly half that of the 6.7-keV
line. The remaining subgroups exhibit soft thermal spectra. Virtually all of
the spectrally-soft X-ray sources can be associated with relatively nearby
coronally-active late-type stars, which are evident as bright near-infrared
(NIR) objects within the X-ray error circles. On a similar basis only a
minority of the spectrally-hard X-ray sources have likely NIR identifications.
The average continuum and Fe-line properties of the spectrally-hard sources are
consistent with those of magnetic cataclysmic variables but the direct
identification of large numbers of such systems in Galactic X-ray surveys,
probing intermediate to faint flux levels, remains challenging.Comment: 14 pages, 9 figures, 4 tables, accepted for publication in MNRA
Deriving an X-Ray Luminosity Function of Dwarf Novae Based on Parallax Measurements
We have derived an X-ray luminosity function using parallax-based distance measurements of a set of 12 dwarf novae, consisting of Suzaku, XMM-Newton and ASCA observations. The shape of the X-ray luminosity function obtained is the most accurate to date, and the luminosities of our sample are concentrated between ~10^{30}-10^{31} erg s^{-1}, lower than previous measurements of X-ray luminosity functions of dwarf novae. Based on the integrated X-ray luminosity function, the sample becomes more incomplete below ~3 x 10^{30} erg s^{-1} than it is above this luminosity limit, and the sample is dominated by X-ray bright dwarf novae. The total integrated luminosity within a radius of 200 pc is 1.48 x 10^{32} erg s^{-1} over the luminosity range of 1 x 10^{28} erg s^{-1} and the maximum luminosity of the sample (1.50 x 10^{32} erg s^{-1}). The total absolute lower limit for the normalised luminosity per solar mass is 1.81 x 10^{26} erg s^{-1} M^{-1}_{solar} which accounts for ~16 per cent of the total X-ray emissivity of CVs as estimated by Sazonov et al. (2006)
Heavy boson production through the collision of an ultrahigh-energy neutrino on a target nucleon
We discuss W and Z production through the deep inelastic neutrino-nucleon
scattering in the context of the standard model SU(3)x SU(2)x U(1) of the
strong and electroweak interactions. We find the cross section rates for the
process neutrino + nucleon --> lepton(-) + W(+) + X for the case of
ultrahigh-energy neutrinos colliding on a target nucleon.Comment: 20 pages, 6 figure
Subtraction at NNLO
We propose a framework for the implementation of a subtraction formalism at
NNLO in QCD, based on an observable- and process-independent cancellation of
infrared singularities. As a first simple application, we present the
calculation of the contribution to the e+e- dijet cross section proportional to
C_F T_RComment: 42 pages Latex; 7 figures included. Modifications to the text, and
references added; the results are unchange
Vector-Meson-Dominance model contribution to
Vector-Meson-Dominance model contribution to is
calculated. The result confirms old estimates that this contribution is much
smaller than the purely electromagnetic photon spliting graph contribution
calculated earlier.Comment: 6 pages, LaTeX, references added, to be published in Physica Script
The serendipituous discovery of a short-period eclipsing polar in 2XMMp
We report the serendipituous discovery of the new eclipsing polar 2XMMp
J131223.4+173659. Its striking X-ray light curve attracted immediate interest
when we were visually inspecting the source products of the 2XMMp catalogue.
This light curve revealed its likely nature as a magnetic cataclysmic variable
of AM Herculis (or polar) type with an orbital period of ~92 min, which was
confirmed by follow-up optical spectroscopy and photometry. 2XMMp
J131223.4+173659 probably has a one-pole accretion geometry. It joins the group
of now nine objects that show no evidence of a soft component in their X-ray
spectra despite being in a high accretion state, thus escaping ROSAT/EUVE
detection. We discuss the likely accretion scenario, the system parameters, and
the spectral energy distribution.Comment: Accepted for publication in A&
Near threshold radiative 3 production in annihilation
We consider the final state in electron-positron
annihilation at cms energies not far from the threshold. Both initial and final
state radiations of the hard photon is considered but without interference
between them. The amplitude for the final state radiation is obtained by using
the effective Wess-Zumino-Witten Lagrangian for pion-photon interactions valid
for low energies. In real experiments energies are never such small that
and mesons would have negligible effect. So a phenomenological
Breit-Wigner factor is introduced in the final state radiation amplitude to
account for the vector mesons influence. Using radiative 3 production
amplitudes, a Monte Carlo event generator was developed which could be useful
in experimental studies.Comment: 15 pages, Latex, 6 figures. Misprints corrected. Version to be
published in JHE
XMM-Newton and Swift observations of WZ Sge: spectral and timing analysis
WZ Sagittae is the prototype object of a subclass of dwarf novae, with rare
and long (super)outbursts, in which a white dwarf primary accretes matter from
a low mass companion. High-energy observations offer the possibility of a
better understanding of the disk-accretion mechanism in WZ Sge-like binaries.
We used archival XMM-Newton and Swift data to characterize the X-ray spectral
and temporal properties of WZ Sge in quiescence. We performed a detailed timing
analysis of the simultaneous X-ray and UV light curves obtained with the EPIC
and OM instruments on board XMM-Newton in 2003. We employed several techniques
in this study, including a correlation study between the two curves. We also
performed an X-ray spectral analysis using the EPIC data, as well as Swift/XRT
data obtained in 2011. We find that the X-ray intensity is clearly modulated at
a period of about 28.96 s, confirming previously published preliminary results.
We find that the X-ray spectral shape of WZ Sge remains practically unchanged
between the XMM-Newton and Swift observations. However, after correcting for
inter-stellar absorption, the intrinsic luminosity is estimated to be about
2.65X10^ 30 erg/s/cm^2 and 1.57X10^30 erg/s/cm^2 in 2003 and 2011,
respectively. During the Swift/XRT observation, the observed flux is a factor
of about 2 lower than that observed by XMM-Newton, but is similar to the
quiescent levels observed various times before the 2001 outburst.Comment: Accepted for publication on A&A.10 pages, 9 figure
Dilepton Production in Nucleon-Nucleon Reactions With and Without Hadronic Inelasticities
We calculate elementary proton-proton and neutron-proton bremsstrahlung and
their contribution to the invariant mass distribution. At 4.9 GeV, the
proton-proton contribution is larger than neutron-proton, but it is small
compared to recent data. We then make a first calculation of bremsstrahlung in
nucleon-nucleon reactions with multi-hadron final states. Again at 4.9 GeV, the
many-body bremsstrahlung is larger than simple nucleon-nucleon bremsstrahlung
by more than an order of magnitude in the low-mass region. When the
bremsstrahlung contributions are summed with Dalitz decay of the ,
radiative decay of the and from two-pion annihilation, the result
matches recent high statistics proton-proton data from the Dilepton
Spectrometer collaboration.Comment: 1+17 pages plus 11 PostScript figures uuencoded and appended,
McGill/93-9, TPI-MINN-93/18-
Analysis of nucleus-nucleus collisions at high energies and Random Matrix Theory
We propose a novel statistical approach to the analysis of experimental data
obtained in nucleus-nucleus collisions at high energies which borrows from
methods developed within the context of Random Matrix Theory. It is applied to
the detection of correlations in momentum distributions of emitted particles.
We find good agreement between the results obtained in this way and a standard
analysis based on the method of effective mass spectra and two-pair correlation
function often used in high energy physics. The method introduced here is free
from unwanted background contributions.Comment: 11 pages, 10 figure
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