1,794 research outputs found
An overview of the EXTraS project: Exploring the X-ray Transient and Variable Sky
The EXTraS project (Exploring the X-ray Transient and variable Sky) will
harvest the hitherto unexplored temporal domain information buried in the
serendipitous data collected by the European Photon Imaging Camera (EPIC)
instrument onboard the ESA XMM-Newton X-ray observatory since its launch. This
will include a search for fast transients, as well as a search and
characterization of 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. X-ray results will be complemented by
multiwavelength characterization of new discoveries. Phenomenological
classification of variable sources will also be performed. All our results will
be made available to the community. A didactic program in selected High Schools
in Italy, Germany and the UK will also be implemented. The EXTraS project
(2014-2016), funded within the EU/FP7 framework, is carried out by a
collaboration including INAF (Italy), IUSS (Italy), CNR/IMATI (Italy),
University of Leicester (UK), MPE (Germany) and ECAP (Germany).Comment: 6 pages, 1 figure. Proceedings of "Swift: 10 years of Discovery", to
appear in Po
On the determination of the spin of the black hole in Cyg X-1 from X-ray reflection spectra
The spin of Cygnus X-1 is measured by fitting reflection models to Suzaku
data covering the energy band 0.9-400 keV. The inner radius of the accretion
disc is found to lie within 2 gravitational radii (r_g=GM/c^2) and a value for
the dimensionless black hole spin is obtained of 0.97^{+0.014}_{-0.02}. This
agrees with recent measurements using the continuum fitting method by Gou et
al. and of the broad iron line by Duro et al. The disc inclination is measured
at 23.7^{+6.7}_{-5.4} deg, which is consistent with the recent optical
measurement of the binary system inclination by Orosz et al of 27+/-0.8 deg. We
pay special attention to the emissivity profile caused by irradiation of the
inner disc by the hard power-law source. The X-ray observations and simulations
show that the index q of that profile deviates from the commonly used,
Newtonian, value of 3 within 3r_g, steepening considerably within 2r_g, as
expected in the strong gravity regime.Comment: 7 pages, 10 figures, MNRAS in pres
Discovery of a Third Harmonic Cyclotron Resonance Scattering Feature in the X-ray Spectrum of 4U 0115+63
We have discovered a third harmonic cyclotron resonance scattering feature
(CRSF) in observations of the recent outburst of 4U 0115+63 with the Rossi
X-ray Timing Explorer (RXTE). The spectrum in a narrow pulse phase range shows
CRSFs at 12.40+0.65/-0.35, 21.45+0.25/-0.38, and 33.56+0.70/-0.90 keV. With
centroid energy ratios to the fundamental of 1.73+/-0.08 and 2.71+/-0.13, the
CRSFs are not harmonically spaced. Strong variability of the continuum and
CRSFs with pulse phase indicate a complex emission geometry near the neutron
star polar cap. In addition, one RXTE observation, which spanned periastron
passage, revealed a strong 2 mHz quasi-periodic oscillation (QPO). This is
slower by two orders of magnitude than the beat-frequency QPO expected in this
system and slower by a factor of more than 5 compared with other QPOs seen in
accreting X-ray pulsars.Comment: To appear in The Astrophysical Journal Letters. 4 pages, 5 figures.
Uses "emulateapj.sty". Revised version includes new figures and additions to
the analysi
The broad iron Kalpha line of Cygnus X-1 as seen by XMM-Newton in the EPIC-pn modified timing mode
We present the analysis of the broadened, flourescent iron Kalpha line in
simultaneous XMM-Newton and RXTE data from the black hole Cygnus X-1. The
XMM-Newton data were taken in a modified version of the timing mode of the
EPIC-pn camera. In this mode the lower energy threshold of the instrument is
increased to 2.8 keV to avoid telemetry drop outs due to the brightness of the
source, while at the same time preserving the signal-to-noise ratio in the Fe
Kalpha band. We find that the best-fit spectrum consists of the sum of an
exponentially cut off power-law and relativistically smeared, ionized
reflection. The shape of the broadened Fe Kalpha feature is due to strong
Compton broadening combined with relativistic broadening. Assuming a standard,
thin accretion disk, the black hole is close to rotating maximally.Comment: Astron. Astrophys., in pres
The XMM-Newton view of the Crab
Aims. We discuss the current X-ray view of the Crab Nebula and Pulsar, summarising our analysis of observations of the source with the EPIC-pn camera on board the XMM-Newton observatory. Different modes of EPIC-pn were combined in order to yield a complete scenario of the spectral properties of the Crab resolved in space and time (pulse phase). In addition we give a description of the special
EPIC-pn Burst mode and guidance for data reduction in that mode.
Methods. We analysed spectra for the nebula and pulsar separately in the 0.6â12.0 keV energy band. All data were processed with the
SAS 6.0.0 XMM-Newton Scientific Analysis System package; models were fitted to the data with XSPEC 11. The high time resolution of EPIC-pn in its Burst mode (7 ÎŒs) was used for a phase resolved analysis of the pulsar spectrum, after determination of the period with epoch folding techniques. Data from the SmallWindow mode were processed and corrected for pile-up allowing for spectroscopy
simultaneously resolved in space and time.
Results. The spatial variation of the spectrum over the entire region of the Crab shows a gradual spectral softening from the inner pulsar region to the outer nebula region with a variation in photon index, Î, from 2.0 to 2.4. Pulse phase resolved spectroscopy of the Crab Pulsar reveals a phase dependent modulation of the photon index in form of a significant hardening of the spectrum in the
inter-peak phase from Î = 1.7 during the pulse peak to Î = 1.5
INTEGRAL-RXTE observations of Cygnus X-1
We present first results from contemporaneous observations of Cygnus X-1 with
INTEGRAL and RXTE, made during INTEGRAL's performance verification phase in
2002 November and December. Consistent with earlier results, the 3-250 keV data
are well described by Comptonization spectra from a Compton corona with a
temperature of kT~50-90 keV and an optical depth of tau~1.0-1.3 plus reflection
from a cold or mildly ionized slab with a covering factor of Omega/2pi~0.2-0.3.
A soft excess below 10 keV, interpreted as emission from the accretion disk, is
seen to decrease during the 1.5 months spanned by our observations. Our results
indicate a remarkable consistency among the independently calibrated detectors,
with the remaining issues being mainly related to the flux calibration of
INTEGRAL.Comment: 6 pages, 3 figures. Figs. 2 and 3 are best viewed in color. Accepted
for publication in the INTEGRAL special edition of A&A
Entanglement measures and the quantum to classical mapping
A quantum model can be mapped to a classical model in one higher dimension.
Here we introduce a finite-temperature correlation measure based on a reduced
density matrix rho_A obtained by cutting the classical system along the
imaginary time (inverse temperature) axis. We show that the von-Neumann entropy
S_ent of rho_A shares many properties with the mutual information, yet is based
on a simpler geometry and is thus easier to calculate. For one-dimensional
quantum systems in the thermodynamic limit we proof that S_ent is non-extensive
for all temperatures T. For the integrable transverse Ising and XXZ models we
demonstrate that the entanglement spectra of rho_A in the limit T-> 0 are
described by free-fermion Hamiltonians and reduce to those of the regular
reduced density matrix---obtained by a spatial instead of an imaginary-time
cut---up to degeneracies.Comment: 5 page
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