1,803 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
Communications of the Lunar and Planetary Laboratory, volume 8, part 3
Infrared photography, mapping, and orbit calculation of natural satellites, comets, and planets in solar syste
The Spectral Variability of Cygnus X-1 at MeV Energies
In previous work, we have used data from the first three years of the CGRO
mission to assemble a broad-band -ray spectrum of the galactic black
hole candidate Cygnus X-1. Contemporaneous data from the COMPTEL, OSSE and
BATSE experiments on CGRO were selected on the basis of the hard X-ray flux
(45--140 keV) as measured by BATSE. This provided a spectrum of Cygnus X-1 in
its canonical low X-ray state (as measured at energies below 10 keV), covering
the energy range from 50 keV to 5 MeV. Here we report on a comparison of this
spectrum to a COMPTEL-OSSE spectrum collected during a high X-ray state of
Cygnus X-1 (May, 1996). These data provide evidence for significant spectral
variability at energies above 1 MeV. In particular, whereas the hard X-ray flux
{\it decreases} during the high X-ray state, the flux at energies above 1 MeV
{\it increases}, resulting in a significantly harder high energy spectrum. This
behavior is consistent with the general picture of galactic black hole
candidates having two distinct spectral forms at soft -ray energies.
These data extend this picture, for the first time, to energies above 1 MeV.Comment: 5 pages, 4 figures, to be published in AIP Conf. Proc., "The Fifth
Compton Symposium
A z~3 radio galaxy and its protocluster: evidence for a superstructure?
We present spectroscopic follow-up observations of Lyman Break Galaxies
(LBGs) selected in the field surrounding the radio galaxy MRC0316-257 at z~3.13
(0316). Robust spectroscopic redshifts are determined for 20 out of 24 objects.
Three of the spectroscopically confirmed galaxies have 3.12<z<3.13 indicating
that these objects reside in a protocluster structure previously found around
the radio galaxy. An additional 5 objects are found 1600 km/s blue-shifted with
respect to the main protocluster structure. This is in addition to three [OIII]
emitters found at this redshift in a previous study. This is further evidence
that a structure exists directly in front of the 0316 protocluster. We estimate
that the foreground structure is responsible for half of the surface
overdensity of LBGs found in the field as a whole. The foreground structure is
associated with a strong surface density peak 1.4 Mpc to the North-West of the
radio galaxy and a 2D Kolmogorov-Smirnov test indicates that the spatial
distributions of the 0316 and foreground galaxies differ at the 3 sigma level.
In addition, we compare the properties of protocluster, foreground structure
and field galaxies, but we find no significant differences. In terms of the
nature of the two structures, a merger scenario is a possible option. Simple
merger dynamics indicates that the observed relative velocity of 1600 km/s can
be reproduced if the two structures have masses of ~5x10^14 Msun and have
starting separations of around 2.5 to 3 Mpc. It is also possible that the
foreground structure is unrelated to the 0316 protocluster in which case the
two structures will not interact before z=0.Comment: 13 pages, 6 figures, accepted for publication in MNRA
Radio Astronomy
Contains reports on four research projects.National Aeronautics and Space Administration (Grant NsG-240-62)National Aeronautics and Space Administration (Grant NsG-419)Lincoln Laboratory (Purchase Order DDL BB-107)U. S. Air Force (Contract AF 19(628)-500)Office of Naval Research (Contract Nonr 3963(02
A deep campaign to characterize the synchronous radio/X-ray mode switching of PSR B0943+10
We report on simultaneous X-ray and radio observations of the mode-switching
pulsar PSR B0943+10 obtained with the XMM-Newton satellite and the LOFAR, LWA
and Arecibo radio telescopes in November 2014. We confirm the synchronous
X-ray/radio switching between a radio-bright (B) and a radio-quiet (Q) mode, in
which the X-ray flux is a factor ~2.4 higher than in the B-mode. We discovered
X-ray pulsations, with pulsed fraction of 38+/-5% (0.5-2 keV), during the
B-mode, and confirm their presence in Q-mode, where the pulsed fraction
increases with energy from ~20% up to ~65% at 2 keV. We found marginal evidence
for an increase in the X-ray pulsed fraction during B-mode on a timescale of
hours. The Q-mode X-ray spectrum requires a fit with a two-component model
(either a power-law plus blackbody or the sum of two blackbodies), while the
B-mode spectrum is well fit by a single blackbody (a single power-law is
rejected). With a maximum likelihood analysis, we found that in Q-mode the
pulsed emission has a thermal blackbody spectrum with temperature ~3.4x10^6 K
and the unpulsed emission is a power-law with photon index ~2.5, while during
B-mode both the pulsed and unpulsed emission can be fit by either a blackbody
or a power law with similar values of temperature and photon index. A Chandra
image shows no evidence for diffuse X-ray emission. These results support a
scenario in which both unpulsed non-thermal emission, likely of magnetospheric
origin, and pulsed thermal emission from a small polar cap (~1500 m^2) with a
strong non-dipolar magnetic field (~10^{14} G), are present during both radio
modes and vary in intensity in a correlated way. This is broadly consistent
with the predictions of the partially screened gap model and does not
necessarily imply global magnetospheric rearrangements to explain the mode
switching.Comment: To be published on The Astrophysical Journa
Central extensions of groups of sections
If q : P -> M is a principal K-bundle over the compact manifold M, then any
invariant symmetric V-valued bilinear form on the Lie algebra k of K defines a
Lie algebra extension of the gauge algebra by a space of bundle-valued 1-forms
modulo exact forms. In the present paper we analyze the integrability of this
extension to a Lie group extension for non-connected, possibly
infinite-dimensional Lie groups K. If K has finitely many connected components
we give a complete characterization of the integrable extensions. Our results
on gauge groups are obtained by specialization of more general results on
extensions of Lie groups of smooth sections of Lie group bundles. In this more
general context we provide sufficient conditions for integrability in terms of
data related only to the group K.Comment: 54 pages, revised version, to appear in Ann. Glob. Anal. Geo
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
First results of the BATSE/COMPTEL/NMSU rapid burst response campaign
The Imaging Compton Telescope (COMPTEL) on board the Compton Gamma Ray Observatory regularly observes gammaâray bursts which occur inside the instrumentâs âŒ1 sr fieldâofâview. COMPTEL images bursts in the 0.75â30 MeV energy range with a typical location accuracy of 1â3 degrees, depending on burst strength, position, duration, and spectrum. COMPTELâs imaging capability has been exploited in order to search for fading gammaâray burst counterparts at other wavelengths through the establishment of a BATSE/COMPTEL/NMSU rapid burst response campaign. This campaign utilizes near realâtime identification and preliminary burst location by BATSE, accelerated COMPTEL imaging, and a worldâwide network of observers to search COMPTEL error boxes as quickly as possible. Timely, deep searches for lingering counterpart emission of several bursts per year are the realized goal of this campaign. During its first year of operation, the rapid response program has been successfully applied to two strong bursts: GRB 930131 and GRB 930309. These bursts were imaged in record time only hours after their occurrence. Subsequently, several observations were made at radio and optical observatories worldâwide
The first multi-wavelength campaign of AXP 4U 0142+61 from radio to hard X-rays
For the first time a quasi-simultaneous multi-wavelength campaign has been
performed on an Anomalous X-ray Pulsar from the radio to the hard X-ray band.
4U 0142+61 was an INTEGRAL target for 1 Ms in July 2005. During these
observations it was also observed in the X-ray band with Swift and RXTE, in the
optical and NIR with Gemini North and in the radio with the WSRT. In this paper
we present the source-energy distribution. The spectral results obtained in the
individual wave bands do not connect smoothly; apparently components of
different origin contribute to the total spectrum. Remarkable is that the
INTEGRAL hard X-ray spectrum (power-law index 0.79 +/- 0.10) is now measured up
to an energy of ~230 keV with no indication of a spectral break. Extrapolation
of the INTEGRAL power-law spectrum to lower energies passes orders of magnitude
underneath the NIR and optical fluxes, as well as the low ~30 microJy (2 sigma)
upper limit in the radio band.Comment: 6 pages, 1 figure. To be published in the proceedings of the
conference "Isolated Neutron Stars: from the Interior to the Surface" (April
24-28, 2006, London, UK), eds. S. Zane, R. Turolla and D. Pag
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