2,292 research outputs found
FUSE Spectra of the Black Hole Binary LMC X-3
Far-ultraviolet spectra of LMC X-3 were taken covering photometric phases
0.47 to 0.74 in the 1.7-day orbital period of the black-hole binary (phase zero
being superior conjunction of the X-ray source). The continuum is faint and
flat, but appears to vary significantly during the observations. Concurrent
RXTE/ASM observations show the system was in its most luminous X-ray state
during the FUSE observations. The FUV spectrum contains strong terrestrial
airglow emission lines, while the only stellar lines clearly present are
emissions from the O VI resonance doublet. Their flux does not change
significantly during the FUSE observations. These lines are modelled as two
asymmetrical profiles, including the local ISM absorptions due to C II and
possibly O VI. Velocity variations of O VI emission are consistent with the
orbital velocity of the black hole and provide a new constraint on its mass.Comment: 12 pages including 1 table, 4 diagrams To appear in A
Large magnetic circular dichroism in resonant inelastic x-ray scattering at the Mn L-edge of Mn-Zn ferrite
We report resonant inelastic x-ray scattering (RIXS) excited by circularly
polarized x-rays on Mn-Zn ferrite at the Mn L2,3-resonances. We demonstrate
that crystal field excitations, as expected for localized systems, dominate the
RIXS spectra and thus their dichroic asymmetry cannot be interpreted in terms
of spin-resolved partial density of states, which has been the standard
approach for RIXS dichroism. We observe large dichroic RIXS at the L2-resonance
which we attribute to the absence of metallic core hole screening in the
insulating Mn-ferrite. On the other hand, reduced L3-RIXS dichroism is
interpreted as an effect of longer scattering time that enables spin-lattice
core hole relaxation via magnons and phonons occurring on a femtosecond time
scale.Comment: 7 pages, 2 figures,
http://link.aps.org/doi/10.1103/PhysRevB.74.17240
Momentum Dependence of Resonant Inelastic X-Ray Scattering Spectrum in Insulating Cuprates
The resonant inelastic x-ray scattering spectrum in insulating cuprates is
examined by using the exact diagonalization technique on small clusters in the
two-dimensional Hubbard model with second and third neighbor hopping terms.
When the incident photon energy is tuned near the Cu K absorption edges, we
find that the features of the unoccupied upper Hubbard band can be extracted
from the spectrum through an anisotropic momentum dependence. They provide an
opportunity for the understanding of the different behavior of hole- and
electron-doped superconductors.Comment: 4 pages with 4 figures, to be published in PR
Our distorted view of magnetars: application of the Resonant Cyclotron Scattering model
The X-ray spectra of the magnetar candidates are customarily fitted with an
empirical, two component model: an absorbed blackbody and a power-law. However,
the physical interpretation of these two spectral components is rarely
discussed. It has been recently proposed that the presence of a hot plasma in
the magnetosphere of highly magnetized neutron stars might distort, through
efficient resonant cyclotron scattering, the thermal emission from the neutron
star surface, resulting in the production of non-thermal spectra. Here we
discuss the Resonant Cyclotron Scattering (RCS) model, and present its XSPEC
implementation, as well as preliminary results of its application to Anomalous
X-ray Pulsars and Soft Gamma-ray Repeaters.Comment: 5 pages, 5 color figures; Astrophysics & Space Science, in press
("Isolated Neutron Stars"; London, UK
An optical parsec-scale jet from a massive young star in the Large Magellanic Cloud
Highly collimated parsec-scale jets, generally linked to the presence of an
accretion disk, are a commonly observed phenomenon from revealed low-mass young
stellar objects. In the past two decades, only a very few of these objects have
been directly (or indirectly) observed towards high-mass (M > 8 M)
young stellar objects, adding to the growing evidence that disk-mediated
accretion is a phenomenon also occurring in high-mass stars, the formation
mechanism of which is still poorly understood. Of the observed jets from
massive young stars, none is in the optical regime (due to these being
typically highly obscured by their native material), and none are found outside
of the Milky Way. Here, we report the detection of HH 1177, the first
extragalactic optical ionized jet originating from a massive young stellar
object located in the Large Magellanic Cloud. The jet is highly collimated over
the entire measured extent of at least 10 pc, and has a bipolar geometry. The
presence of a jet indicates ongoing, disk-mediated accretion, and together with
the high degree of collimation, this system is therefore likely to be an
up-scaled version of low-mass star formation. We conclude that the physics
governing jet launching and collimation is independent of stellar mass.Comment: 9 pages, 5 figures, 2 table
Dichotomous Hamiltonians with Unbounded Entries and Solutions of Riccati Equations
An operator Riccati equation from systems theory is considered in the case
that all entries of the associated Hamiltonian are unbounded. Using a certain
dichotomy property of the Hamiltonian and its symmetry with respect to two
different indefinite inner products, we prove the existence of nonnegative and
nonpositive solutions of the Riccati equation. Moreover, conditions for the
boundedness and uniqueness of these solutions are established.Comment: 31 pages, 3 figures; proof of uniqueness of solutions added; to
appear in Journal of Evolution Equation
Somatic reversion events point towards RPL4 as a novel disease gene in a condition resembling Diamond-Blackfan anemia.
Discovery of luminous pulsed hard X-ray emission from anomalous X-ray pulsars 1RXS J1708-4009, 4U 0142+61 and 1E 2259+586 by INTEGRAL and RXTE
We report on the discovery of hard spectral tails for energies above 10 keV
in the total and pulsed spectra of anomalous X-ray pulsars 1RXS J1708-4009, 4U
0142+61 and 1E 2259+586 using RXTE PCA (2-60 keV) and HEXTE (15-250 keV) data
and INTEGRAL IBIS ISGRI (20-300 keV) data. Improved spectral information on 1E
1841-045 is presented. The pulsed and total spectra measured above 10 keV have
power-law shapes and there is so far no significant evidence for spectral
breaks or bends up to ~150 keV. The pulsed spectra are exceptionally hard with
indices measured for 4 AXPs approximately in the range -1.0 -- 1.0. We also
reanalyzed archival CGRO COMPTEL (0.75-30 MeV) data to search for signatures
from our set of AXPs. No detections can be claimed, but the obtained
upper-limits in the MeV band indicate that for 1RXS J1708-4009, 4U 0142+61 and
1E 1841-045 strong breaks must occur somewhere between 150 and 750 keV.Comment: Accepted for publication in ApJ; 19 pages; 4 Tables; 15 Figures (6
color
BeppoSAX measurements of the bright gamma-ray burst 010222
We analyze the BeppoSAX measurements of the prompt and afterglow emission of
the gamma-ray burst GRB010222. Among 45 GRBs detected with the Wide Field
Cameras on BeppoSAX, the 40-700 keV fluence of (9.3+/-0.3)E-5 erg cm-2 is only
surpassed by GRB990123. In terms of the isotropic 20-2000 keV energy output of
7.8E53 erg, it ranks third of all GRBs with measured distances. Since this
burst is so bright, the data provide complete and valuable coverage up to 65 hr
after the event, except for a gap between 3.5 and 8.0 hr. The 2-10 keV flux
history shows clear signs of a break which is consistent with a break seen in
the optical, and provides supporting evidence for the achromatic nature of the
break. An explanation for the break in the context of a collimated expansion is
not straightforward. Rather, a model is favored whereby the fireball is braked
to the non-relativistic regime quickly (within a fraction of day) by a dense
1E6 cm-3 circumburst medium. This implies that, after a mild beaming
correction, GRB010222 may be the most energetic burst observed thus far. The
X-ray decay index after the break is 1.33+/-0.04, the spectral index
0.97+/-0.05. The decay is, with unprecedented accuracy, identical to that
observed in the optical.Comment: Accepted on June 6 for publication in ApJ part I. Publication due in
October 2001. Accepted version has only minor modification
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