2,547 research outputs found
The First Detection of [O IV] from an Ultraluminous X-ray Source with Spitzer. II. Evidence for High Luminosity in Holmberg II ULX
This is the second of two papers examining Spitzer Infrared Spectrograph
(IRS) observations of the ultraluminous X-ray source (ULX) in Holmberg II. Here
we perform detailed photoionization modeling of the infrared lines. Our
analysis suggests that the luminosity and morphology of the [O IV] 25.89 m
emission line is consistent with photoionization by the soft X-ray and far
ultraviolet (FUV) radiation from the accretion disk of the binary system and
inconsistent with narrow beaming. We show that the emission nebula is
matter-bounded both in the line of sight direction and to the east, and
probably radiation-bounded to the west. A bolometric luminosity in excess of
10 erg s would be needed to produce the measured [O IV] flux. We
use modeling and previously published studies to conclude that shocks likely
contribute very little, if at all, to the high-ionization line fluxes observed
in the Holmberg II ULX. Additionally, we find that the spectral type of the
companion star has a surprisingly strong effect on the predicted strength of
the [O IV] emission. This finding could explain the origin of [O IV] in some
starburst systems containing black hole binaries.Comment: Accepted by Ap
Towards an -theorem for granular gases
The -theorem, originally derived at the level of Boltzmann non-linear
kinetic equation for a dilute gas undergoing elastic collisions, strongly
constrains the velocity distribution of the gas to evolve irreversibly towards
equilibrium. As such, the theorem could not be generalized to account for
dissipative systems: the conservative nature of collisions is an essential
ingredient in the standard derivation. For a dissipative gas of grains, we
construct here a simple functional related to the original ,
that can be qualified as a Lyapunov functional. It is positive, and results
backed by three independent simulation approaches (a deterministic spectral
method, the stochastic Direct Simulation Monte Carlo technique, and Molecular
Dynamics) indicate that it is also non-increasing. Both driven and unforced
cases are investigated
A CFD analysis of the influence of plenum configurations on gas distribution in a fluidized bed
Fluidized beds are widely used in many industries. The fluidization quality of these units is strongly related to the characteristics of the plenum and distributor (grid). In this work, the effect of different plenum geometries, and gas entrance sizes and locations on the velocity profile above the distributor was analyzed by Computational Fluid Dynamics (CFD). The results showed that flow uniformity above the distributor improved with an increase in the gas inlet diameter and the plenum height. Channeling was observed for the bottom central inlet. Addition-ally, simulations for plenum heights predicted by one of the frequently used correlations (Litz correlation) were also carried out and showed, especially for a bot-tom central gas inlet, a poor quality flow distribution. This behavior indicated that Litz correlation tends to underestimate the plenum height for obtaining a uni-form flow downstream the distributor.Fil: Soria, Jose Miguel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigación y Desarrollo en Ingeniería de Procesos, Biotecnología y Energías Alternativas. Universidad Nacional del Comahue. Instituto de Investigación y Desarrollo en Ingeniería de Procesos, Biotecnología y Energías Alternativas; ArgentinaFil: Ausina, T. M.. Universidad Nacional del Comahue; ArgentinaFil: Mazza, German Delfor. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigación y Desarrollo en Ingeniería de Procesos, Biotecnología y Energías Alternativas. Universidad Nacional del Comahue. Instituto de Investigación y Desarrollo en Ingeniería de Procesos, Biotecnología y Energías Alternativas; Argentin
Tear proteomic profiling with MALDI-TOF mass spectrometry coupled with magnetic-beads HIC-18 separation as a diagnostic tools in blepharitis disease
Comunicaciones a congreso
Quasi-Periodic Variability in NGC 5408 X-1
We report the discovery with XMM-Newton of quasiperiodic variability in the
0.2 - 10 keV X-ray flux from the ultraluminous X-ray source NGC 5408 X-1. The
average power spectrum of all EPIC-pn data reveals a strong 20 mHz QPO with an
average amplitude (rms) of 9%, and a coherence of Q~6. In a 33 ksec time
interval when the 20 mHz QPO is strongest we also find evidence for a 2nd QPO
peak at 15 mHz. This is the first indication for a close pair of QPOs in a ULX
source. Interestingly, the frequency ratio of this QPO pair is inconsistent
with 3:2 at the 3sigma level, but is consistent with a 4:3 ratio. A powerlaw
noise component with slope near 1.5 is also present below 0.1 Hz with evidence
for a break to a flatter slope at about 3 mHz. The source shows substantial
broadband variability, with a total amplitude (rms) of about 30% in the 0.1 -
100 mHz frequency band, and there is strong energy dependence to the
variability. We discuss the implications of these findings in the context of
models for ULXs, and their implications for the object's mass.Comment: 23 pages, 7 figures. Accepted for publication in the Astrophysical
Journa
Discovery of an optical counterpart to the hyperluminous X-ray source in ESO 243-49
The existence of black holes of masses ~ 10^2-10^5 Msun has important
implications for the formation and evolution of star clusters and supermassive
black holes. One of the strongest candidates to date is the hyperluminous X-ray
source HLX1, possibly located in the S0-a galaxy ESO243-49, but the lack of an
identifiable optical counterpart had hampered its interpretation. Using the
Magellan telescope, we have discovered an unresolved optical source with R =
(23.80 +/- 0.25) mag and V = (24.5 +/- 0.3) mag within HLX1's positional error
circle. This implies an average X-ray/optical flux ratio ~ 500. Taking the same
distance as ESO243-49, we obtain an intrinsic brightness M_R = (-11.0 +/- 0.3)
mag, comparable to that of a massive globular cluster. Alternatively, the
optical source is consistent with a main-sequence M star in the Galactic halo
(for example an M4.4 star at ~ 2.5 kpc). We also examined the properties of
ESO243-49 by combining Swift/UVOT observations with stellar population
modelling. We found that the overall emission is dominated by a ~5 Gyr old
stellar population, but the UV emission at ~2000 Ang is mostly due to ongoing
star-formation at a rate of ~ 0.03 Msun/yr. The UV emission is more intense (at
least a 9-sigma enhancement above the mean) North East of the nucleus, in the
same quadrant as HLX1. With the combined optical and X-ray measurements, we put
constraints on the nature of HLX1. We rule out a foreground star and a
background AGN. Two alternative scenarios are still viable. HLX1 could be an
accreting intermediate-mass black hole in a star cluster, which may itself be
the stripped nucleus of a dwarf galaxy that passed through ESO243-49, an event
which might have caused the current episode of star formation. Or, it could be
a neutron star in the Galactic halo, accreting from an M4-M5 donor star.Comment: 7 pages, accepted by MNRAS. Several improvements from Oct 7 version:
stronger evidence of the optical counterpart; more accurate estimate of its
brightness (a factor of 2 brighter than previously estimated); use of a
larger set of Swift/UVOT data to measure the recent star formation rate in
ESO243-49; improved discussion and comparison of the competing scenario
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