3,851 research outputs found
Discovery of pulsations in the X-ray transient 4U 1901+03
We describe observations of the 2003 outburst of the hard-spectrum X-ray
transient 4U 1901+03 with the Rossi X-ray Timing Explorer. The outburst was
first detected in 2003 February by the All-Sky Monitor, and reached a peak
2.5-25 keV flux of 8x10^-9 ergs/cm^2/s (around 240 mCrab). The only other known
outburst occurred 32.2 yr earlier, likely the longest presently known
recurrence time for any X-ray transient. Proportional Counter Array (PCA)
observations over the 5-month duration of the 2003 outburst revealed a 2.763 s
pulsar in a 22.58 d orbit. The detection of pulsations down to a flux of
3x10^-11 ergs/cm^2/s (2.5-25 keV), along with the inferred long-term accretion
rate of 8.1x10^-11 M_sun/yr (assuming a distance of 10 kpc) suggests that the
surface magnetic field strength is below ~5x10^11 G. The corresponding
cyclotron energy is thus below 4 keV, consistent with the non-detection of
resonance features at high energies. Although we could not unambiguously
identify the optical counterpart, the lack of a bright IR candidate within the
1' RXTE error circle rules out a supergiant mass donor. The neutron star in 4U
1901+03 probably accretes from the wind of a main-sequence O-B star, like most
other high-mass binary X-ray pulsars. The almost circular orbit e=0.036
confirms the system's membership in a growing class of wide, low-eccentricity
systems in which the neutron stars may have received much smaller kicks as a
result of their natal supernova explosions.Comment: 7 pages, 6 figures, accepted by ApJ. Very minor addition in response
to referee's comment; updated author affiliatio
Self-consistent models for Coulomb heated X-ray pulsar atmospheres
Calculations of accreting magnetized neutron star atmospheres heated by the gradual deceleration of protons via Coulomb collisions are presented. Self consistent determinations of the temperature and density structure for different accretion rates are made by assuming hydrostatic equilibrium and energy balance, coupled with radiative transfer. The full radiative transfer in two polarizations, using magnetic cross sections but with cyclotron resonance effects treated approximately, is carried out in the inhomogeneous atmospheres
The Cosmic Censor Forbids Naked Topology
For any asymptotically flat spacetime with a suitable causal structure
obeying (a weak form of) Penrose's cosmic censorship conjecture and satisfying
conditions guaranteeing focusing of complete null geodesics, we prove that
active topological censorship holds. We do not assume global hyperbolicity, and
therefore make no use of Cauchy surfaces and their topology. Instead, we
replace this with two underlying assumptions concerning the causal structure:
that no compact set can signal to arbitrarily small neighbourhoods of spatial
infinity (``-avoidance''), and that no future incomplete null geodesic is
visible from future null infinity. We show that these and the focusing
condition together imply that the domain of outer communications is simply
connected. Furthermore, we prove lemmas which have as a consequence that if a
future incomplete null geodesic were visible from infinity, then given our
-avoidance assumption, it would also be visible from points of spacetime
that can communicate with infinity, and so would signify a true naked
singularity.Comment: To appear in CQG, this improved version contains minor revisions to
incorporate referee's suggestions. Two revised references. Plain TeX, 12
page
Chandra observations of the millisecond X-ray pulsar IGR J00291+5934 in quiescence
In this Paper we report on our analysis of three Chandra observations of the
accretion-powered millisecond X-ray pulsar IGR J00291+5934 obtained during the
late stages of the 2004 outburst. We also report the serendipitous detection of
the source in quiescence by ROSAT during MJD 48830-48839. The detected 0.3-10
keV source count rates varied significantly between the Chandra observations
from (7.2+-1.2)x10^-3, (6.8+-0.9)x10^-3, and (1.4+-0.1)x10^-2 counts per second
for the 1st, 2nd, and 3rd Chandra observation, on MJD 53371.88, 53383.99, and
53407.57, respectively. The count rate for the 3rd observation is 2.0+-0.4
times as high as that of the average of the first two observations. The
unabsorbed 0.5-10 keV source flux for the best-fit power-law model to the
source spectrum was (7.9+-2.5)x10^-14, (7.3+-2.0)x10^-14, and
(1.17+-0.22)x10^-13 erg cm^-2 s^-1 for the 1st, 2nd, and 3rd Chandra
observation, respectively. We find that this source flux is consistent with
that found by ROSAT [~(5.4+-2.4)x10^-14 erg cm^-2 s^-1]. Under the assumption
that the interstellar extinction, N_H, does not vary between the observations,
we find that the blackbody temperature during the 2nd Chandra observation is
significantly higher than that during the 1st and 3rd observation. Furthermore,
the effective temperature of the neutron star derived from fitting an absorbed
blackbody or neutron star atmosphere model to the data is rather high in
comparison with many other neutron star soft X-ray transients in quiescence,
even during the 1st and 3rd observation. If we assume that the source quiescent
luminosity is similar to that measured for two other accretion powered
millisecond pulsars in quiescence, the distance to IGR J00291+5934 is 2.6-3.6
kpc.Comment: 7 pages, 3 Figures, accepted for publication in MNRA
On the Gannon-Lee Singularity Theorem in Higher Dimensions
The Gannon-Lee singularity theorems give well-known restrictions on the
spatial topology of singularity-free (i.e., nonspacelike geodesically
complete), globally hyperbolic spacetimes. In this paper, we revisit these
classic results in the light of recent developments, especially the failure in
higher dimensions of a celebrated theorem by Hawking on the topology of black
hole horizons. The global hyperbolicity requirement is weakened, and we expand
the scope of the main results to allow for the richer variety of spatial
topologies which are likely to occur in higher-dimensional spacetimes.Comment: 13 pages, no figures, to appear in Class. Quantum Gra
Charmonium properties from lattice QCD + QED: hyperfine splitting, leptonic width, charm quark mass and
We have performed the first lattice QCD computations of the
properties (masses and decay constants) of ground-state charmonium mesons. Our
calculation uses the HISQ action to generate quark-line connected two-point
correlation functions on MILC gluon field configurations that include
quark masses going down to the physical point, tuning the quark mass from
and including the effect of the quark's electric charge
through quenched QED. We obtain (connected) =
120.3(1.1) MeV and interpret the difference with experiment as the impact on
of its decay to gluons, missing from the lattice calculation. This
allows us to determine =+7.3(1.2) MeV,
giving its value for the first time. Our result of 0.4104(17)
GeV, gives =5.637(49) keV, in agreement
with, but now more accurate than experiment. At the same time we have improved
the determination of the quark mass, including the impact of quenched QED
to give = 0.9841(51) GeV. We have also used
the time-moments of the vector charmonium current-current correlators to
improve the lattice QCD result for the quark HVP contribution to the
anomalous magnetic moment of the muon. We obtain , which is 2.5 higher than the value derived using moments
extracted from some sets of experimental data on . This value for includes our determination of
the effect of QED on this quantity, .Comment: Added extra discussion on QED setup, some new results to study the
effects of strong isospin breaking in the sea (including new Fig. 1) and a
fit stability plot for the hyperfine splitting (new Fig. 7). Version accepted
for publication in PR
On the topology of stationary black holes
We prove that the domain of outer communication of a stationary, globally
hyperbolic spacetime satisfying the null energy condition must be simply
connected. Under suitable additional hypotheses, this implies, in particular,
that each connected component of a cross-section of the event horizon of a
stationary black hole must have spherical topology.Comment: 7 pages, Late
Transformation between Australian datums using a modified transverse Mercator projection
The introduction of the Geocentric Datum of Australia (GDA94) in the year 2000 will undoubtedly require the transformation of a large amount of coordinate data in Australia. This paper presents a modified transverse Mercator (MTM) map-projection such that the latitude and longitude on one datum are projected so that they closely agree with the transverse Mercator easting and northing on another datum. This approach will allow the introduction of the GDA94 whilst preserving Australian Map Grid (AMG) coordinates. Conversely, the MTM projection can be used to transform coordinates directly from the Australian Geodetic Datum (AGD) to the new Map Grid of Australia (MGA94). In order to test these two approaches, MTM parameters have been computed from 82 co-located GDA94/MGA94 and AGD98/AMG84 coordinates that comprise the Western Australian STATEFIX geodetic network. When using the national seven- and three-parameter datum transformations, the maximum differences between observed and transformed coordinates are 2.04m and 2.21m, respectively. When using the transformation by MTM projection, the projected coordinates agree with the observed coordinates to less than 2.04m
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