403 research outputs found
Study of Beta Equilibrated 2+1 Flavor Quark Matter in PNJL Model
We report a first case study of the phase diagram of 2+1 flavor strongly
interacting matter in equilibrium, using the
PolyakovNambuJona-Lasinio model. Physical characteristics of relevant
thermodynamic observables have been discussed. A comparative analysis with the
corresponding observables in the Nambu-Jona-Lasinio model is presented. We find
distinct differences between the models in terms of a number of thermodynamic
quantities like the speed of sound, specific heat, various number densities as
well as entropy. The present study is expected to give us a better insight into
the role that the superdense matter created in heavy ion collision experiments
play in our understanding of the properties of matter inside the core of
supermassive stars in the Universe
Radial oscillations of relativistic stars
We present a new survey of the radial oscillation modes of neutron stars.
This study complements and corrects earlier studies of radial oscillations. We
present an extensive list of frequencies for the most common equations of state
and some more recent ones. In order to check the accuracy, we use two different
numerical schemes which yield the same results. The stimulation for this work
comes from the need of the groups that evolve the full nonlinear Einstein
equation to have reliable results from perturbation theory for comparison.Comment: 8 pages, 1 figure, 20 tables, accepted for publication in A&
Last orbits of binary strange quark stars
We present the first relativistic calculations of the final phase of inspiral
of a binary system consisting of two stars built predominantely of strange
quark matter (strange quark stars). We study the precoalescing stage within the
Isenberg-Wilson-Mathews approximation of general relativity using a multidomain
spectral method. A hydrodynamical treatment is performed under the assumption
that the flow is either rigidly rotating or irrotational, taking into account
the finite density at the stellar surface -- a distinctive feature with respect
to the neutron star case. The gravitational-radiation driven evolution of the
binary system is approximated by a sequence of quasi-equilibrium configurations
at fixed baryon number and decreasing separation. We find that the innermost
stable circular orbit (ISCO) is given by an orbital instability both for
synchronized and irrotational systems. This constrasts with neutron stars for
which the ISCO is given by the mass-shedding limit in the irrotational case.
The gravitational wave frequency at the ISCO, which marks the end of the
inspiral phase, is found to be 1400 Hz for two irrotational 1.35 Msol strange
stars and for the MIT bag model of strange matter with massless quarks and a
bag constant B=60 MeV/fm^3. Detailed comparisons with binary neutrons star
models, as well as with third order Post-Newtonian point-mass binaries are
given.Comment: 11 pages, 10 figures, improved conclusion and figures, references
added, accepted for publication in Phys. Rev.
The average X-ray/gamma-ray spectrum of radio-quiet Seyfert 1s
We have obtained the average 1--500 keV spectrum of radio-quiet Seyfert 1s
using data from EXOSAT, Ginga, HEAO, and GRO/OSSE. The spectral fit to the
combined average EXOSAT and OSSE data is fully consistent with that for Ginga
and OSSE, confirming results from an earlier Ginga/OSSE sample. The average
spectrum is well-fitted by a power-law X-ray continuum with an energy spectral
index of moderately absorbed by an ionized medium and with
a Compton reflection component. A high-energy cutoff (or a break) in the the
power-law component at a few hundred keV or more is required by the data. We
also show that the corresponding average spectrum from HEAO A1 and A4 is fully
compatible with that obtained from EXOSAT, Ginga and OSSE. These results
confirm that the apparent discrepancy between the results of Ginga (with
) and the previous results of EXOSAT and HEAO (with ) is indeed due to ionized absorption and Compton reflection first
taken into account for Ginga but not for the previous missions. Also, our
results confirm that the Seyfert-1 spectra are on average cut off in gamma-rays
at energies of at least a few hundred keV, not at keV (as suggested
earlier by OSSE data alone). The average spectrum is compatible with emission
from either an optically-thin relativistic thermal plasma in a disk corona, or
with a nonthermal plasma with a power-law injection of relativistic electrons.Comment: 7 pages, 3 Postscript figures, MNRAS accepte
Comparisons of various model fits to the Iron line profile in MCG-6-30-15
The broad Iron line in MCG-6-30-15 is fitted to the Comptonization model
where line broadening occurs due to Compton down-scattering in a highly ionized
optically thick cloud. These results are compared to the disk line model where
the broadening is due to Gravitational/Doppler effects in the vicinity of a
black hole. We find that both models fit the data well and it is not possible
to differentiate between them by fitting only the ASCA data. The best fit
temperature and optical depth of the cloud are found to be kT = 0.54 keV and
from the Comptonization model. This model further suggests that
while the temperature can be assumed to be constant, the optical depth varies
during the observation period. We emphasis an earlier conclusion that
simultaneous broad band data ( keV) can rule out (or confirm) the
Comptonization model.Comment: 4 figures. uses aasms4.sty, accepted by ApJ, email:
[email protected]
Detecting Compton Reflection and a Broad Iron Line in MCG-5-23-16 with the Rossi X-ray Timing Explorer
We report the detection with the Rossi X-ray Timing Explorer of a Compton
reflection signature in the Seyfert galaxy MCG-5-23-16. RXTE also resolves the
Fe K-alpha fluorescence line with FWHM ~48,000 km s^{-1}. This measurement
provides the first independent confirmation of ASCA detections in Seyfert
galaxies of broad Fe K-alpha lines that are thought to be the signature of
emission from the inner regions of an accretion disk orbiting a black hole.
Under the assumption that reflection arises from an isotropic source located
above a neutral accretion disk, and using a theoretical model that accounts for
the dependence of the reflected spectrum on inclination angle, we derive a 90%
confidence range for the disk inclination of i = 50 to 81 degrees. The large
inclination is consistent with that expected from the unified model for
MCG-5-23-16 based on its Seyfert 1.9 classification. If we assume that the
high-energy cutoff in the incident spectrum lies at energies larger than a few
hundred keV, then the equivalent width of the Fe K-alpha line is much larger
than predicted for the amount of reflection. This implies either an enhanced
iron abundance, a covering factor of reflecting material > 0.5, or a cutoff in
the incident spectrum at energies between ~60 and ~200 keV.Comment: Accepted for publication in ApJ, LaTeX. 14 pages including 3 figures,
with 1 table as a separate postscript file. Typo corrected in abstrac
Effect of hot water immersion on acute physiological responses following resistance exercise
Purpose: Hot water immersion (HWI) is a strategy theorised to enhance exercise recovery. However, the acute physiological responses to HWI following resistance exercise are yet to be determined.
Methods: The effect of HWI on intramuscular temperature (IMT), muscle function, muscle soreness and blood markers of muscle cell disruption and inflammatory processes after resistance exercise was assessed. Sixteen resistance trained males performed resistance exercise, followed by either 10 min HWI at 40°C or 10 min passive recovery (PAS).
Results: Post-intervention, the increase in IMT at all depths was greater for HWI compared to PAS, however this difference had disappeared by 1 h post at depths of 1 and 2 cm, and by 2 h post at a depth of 3 cm. There were no differences between groups for muscle function, muscle soreness or any blood markers.
Conclusion: These results suggest that HWI is a viable means of heat therapy to support a greater IMT following resistance exercise. Recovery of muscle function and muscle soreness is independent of acute changes in IMT associated with HWI
Frequency-dependent time lags in the X-ray emission of the Seyfert galaxy NGC 7469
We report the discovery of time lags in the cross-spectra of the X-ray light
curves of the Seyfert galaxy NGC 7469. This behavior is common in Galactic
black hole and neutron star binaries, and is in the sense that harder X-rays
are delayed with respect to the soft with a time lag approximately proportional
to the Fourier period. At the longest period probed by our observation we find
a time lag of approximately 3.5 hours between the 2-4 and 4-10 keV X-rays. A
similar lag and period dependence is found comparing the 2-4 and 10-15 keV
light curves, albeit with less significance. We find the coherence function of
the light curves to be close to 1. The implications of these results for the
X-ray production mechanism in active galactic nuclei (AGN) is discussed.Comment: 12 pages, 2 figures, accepted for Publication in ApJ
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