450 research outputs found
Discovery of a new accreting millisecond X-ray pulsar in the globular cluster NGC 2808
We report on the discovery of coherent pulsations at a period of 2.9 ms from
the X-ray transient MAXI J0911-655 in the globular cluster NGC 2808. We
observed X-ray pulsations at a frequency of Hz in three different
observations of the source performed with XMM-Newton and NuSTAR during the
source outburst. This newly discovered accreting millisecond pulsar is part of
an ultra-compact binary system characterised by an orbital period of
minutes and a projected semi-major axis of lt-ms. Based on the mass
function we estimate a minimum companion mass of 0.024 M, which
assumes a neutron star mass of 1.4 M and a maximum inclination angle
of (derived from the lack of eclipses and dips in the light-curve
of the source). We find that the companion star's Roche-Lobe could either be
filled by a hot ( K) pure helium white dwarf with a 0.028
M mass (implying ) or an old (>5 Gyr) brown dwarf
with metallicity abundances between solar/sub-solar and mass ranging in the
interval 0.0650.085 M (16 < < 21). During the outburst the
broad-band energy spectra are well described by a superposition of a weak
black-body component (kT 0.5 keV) and a hard cutoff power-law with photon
index 1.7 and cut-off at a temperature kT 130 keV. Up to
the latest Swift-XRT observation performed on 2016 July 19 the source has been
observed in outburst for almost 150 days, which makes MAXI J0911-655 the second
accreting millisecond X-ray pulsar with outburst duration longer than 100 days.Comment: 7 pages, 5 figures, accepted for publication in A&
Absence-like seizures in adult rats following pilocarpine-induced status epilepticus early in life
Administration of pilocarpine causes epilepsy in rats if status epilepticus (SE) is induced at an early age. To determine in detail the electrophysiological patterns of the epileptogenic activity in these animals, 46 Wistar rats, 7-17 days old, were subjected to SE induced by pilocarpine and electro-oscillograms from the cortex, hippocampus, amygdala, thalamus and hypothalamus, as well as head, rostrum and vibrissa, eye, ear and forelimb movements, were recorded 120 days later. Six control animals of the same age range did not show any signs of epilepsy. In all the rats subjected to SE, iterative spike-wave complexes (8.1 ± 0.5 Hz in frequency, 18.9 ± 9.1 s in duration) were recorded from the frontal cortex during absence fits. However, similar spike-wave discharges were always found also in the hippocampus and, less frequently, in the amygdala and in thalamic nuclei. Repetitive or single spikes were also detected in these same central structures. Clonic movements and single jerks were recorded from all the rats, either concomitantly with or independently of the spike-wave complexes and spikes. We conclude that rats made epileptic with pilocarpine develop absence seizures also occurring during paradoxical sleep, showing the characteristic spike-wave bursts in neocortical areas and also in the hippocampus. This is in contrast to the well-accepted statement that one of the main characteristics of absence-like fits in the rat is that spike-wave discharges are never recorded from the hippocampal fields.Universidade de São Paulo Faculdade de Medicina Laboratório de Neurocirurgia FuncionalUniversidade Federal de São Paulo (UNIFESP) Escola Paulista de Medicina Laboratório de Neurologia ExperimentalUNIFESP, EPM, Laboratório de Neurologia ExperimentalSciEL
Rickettsia typhi and Haemophagocytic Syndrome
Appropriate therapy (dexamethasone, cyclosporin,
and etoposide) could save the patient in those cases in which the
pathogen-direct therapy has not been sufficient by itself to control
the disease
Discovery of a soft X-ray 8 mHz QPO from the accreting millisecond pulsar IGR J00291+5934
In this paper, we report on the analysis of the peculiar X-ray variability
displayed by the accreting millisecond X-ray pulsar IGR J00291+5934 in a 80
ks-long joint NuSTAR and XMM-Newton observation performed during the source
outburst in 2015. The light curve of the source was characterized by a
flaring-like behavior, with typical rise and decay time scales of ~120 s. The
flares are accompanied by a remarkable spectral variability, with the X-ray
emission being generally softer at the peak of the flares. A strong quasi
periodic oscillation (QPO) is detected at ~8 mHz in the power spectrum of the
source and clearly associated with the flaring-like behavior. This feature has
the strongest power at soft X-rays (<3 keV). We carried out a dedicated
hardness-ratio resolved spectral analysis and a QPO phase-resolved spectral
analysis, together with an in-depth study of the source timing properties, to
investigate the origin of this behavior. We suggest that the unusual
variability of IGR J00291+5934 observed by XMM-Newton and NuSTAR could be
produced by an heartbeat-like mechanism, similar to that operating in
black-hole X-ray binaries. The possibility that this variability, and the
associated QPO, are triggered by phases of quasi-stable nuclear burning, as
suggested in the literature for a number of other neutron star binaries
displaying a similar behavior, cannot be solidly tested in the case of IGR
J00291+5934 due to the paucity of type-I X-ray bursts observed from this
source.Comment: Submitted to MNRAS on 23 Sept 2016. Modified according to the
referee's suggestions. Comments are welcomed. One reference updated in this
versio
Post-neurosurgical multidrug-resistant Acinetobacter baumannii meningitis successfully treated with intrathecal colistin. A new case and a systematic review of the literature
Introduction: Post-neurosurgical nosocomial meningitis has become an important subgroup of bacterial
meningitis in the hospital setting. The increase in meningitis caused by multidrug-resistant (MDR)
Acinetobacter baumannii has resulted in a significant reduction in available treatment options.
Case report and literature review: We report the case of a 36-year-old man with a complex craniofacial
trauma, who developed a nosocomial meningitis due to MDR A. baumannii that was cured by intrathecal
colistin. The case is contextualized among all the published cases of Acinetobacter meningitis treated
with topical colistin found through a MEDLINE search of the literature. To date, including the present
case, eight reported cases of Acinetobacter meningitis have been treated with colistin administered by an
intrathecal route and 24 by an intraventricular route. The daily dose of colistin used ranged from 1.6 mg
every 24 h to 20 mg every 24 h in adult patients. Themedian time necessary to obtain cerebrospinal fluid
sterilization was 4.1 days, and treatment was always successful even if in two cases Acinetobacter
meningitis relapsed. Toxicity probably or possibly related to the topical administration of colistin was
noted in five out of the 32 patients.
Conclusions: Topical colistin can be an effective and safe treatment for MDR Acinetobacter meningitis
Rickettsiosis with Pleural Effusion: A Systematic Review with a Focus on Rickettsiosis in Italy
Background: Motivated by a case finding of Mediterranean spotted fever (MSF) associated with atypical pneumonia and pleural effusion in which Rickettsia conorii subsp. israelensis was identified by molecular methods in the pleural fluid, we wanted to summarize the clinical presentations of rickettsiosis in Italy by systematic research and to make a systematic review of all the global cases of rickettsiosis associated with pleural effusion. Methods: For the literature search, the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) methodology was followed. We chose to select only the studies published in last 25 years and confirmed both with serological and molecular assays. Results: Human cases of rickettsiosis in Italy were reported in 48 papers describing 2831 patients with very different clinical presentations; the majority was MSF accounted to R. conorii and was reported in Sicily. Pleural effusion associated with infection with microorganisms belonging to Rickettsiales was described in 487 patients. It was rarely associated with microorganisms different from O. tsutsugamushi; also rarely, cases of scrub typhus were reported outside Southeast Asia and in the largest majority, the diagnosis was achieved with serology. Conclusions: MSF, especially when caused by R. conorii subsp. israelensis, may be a severe disease. A high index of suspicion is required to promptly start life-saving therapy. Pleural effusion and interstitial pneumonia may be part of the clinical picture of severe rickettsial disease and should not lead the physician away from this diagnosis
Spectral and timing properties of IGR J00291+5934 during its 2015 outburst
We report on the spectral and timing properties of the accreting millisecond
X-ray pulsar IGR J00291+5934 observed by XMM-Newton and NuSTAR during its 2015
outburst. The source is in a hard state dominated at high energies by a
comptonization of soft photons ( keV) by an electron population with
kT keV, and at lower energies by a blackbody component with
kT keV. A moderately broad, neutral Fe emission line and four narrow
absorption lines are also found. By investigating the pulse phase evolution, we
derived the best-fitting orbital solution for the 2015 outburst. Comparing the
updated ephemeris with those of the previous outbursts, we set a
confidence level interval s/s s/s on the orbital period derivative. Moreover, we
investigated the pulse profile dependence on energy finding a peculiar
behaviour of the pulse fractional amplitude and lags as a function of energy.
We performed a phase-resolved spectroscopy showing that the blackbody component
tracks remarkably well the pulse-profile, indicating that this component
resides at the neutron star surface (hot-spot).Comment: 9 pages, 7 figures. Accepted for publication in MNRA
A possible cyclotron resonance scattering feature near 0.7 keV in X1822-371
We analyse all available X-ray observations of X1822-371 made with
XMM-Newton, Chandra, Suzaku and INTEGRAL satellites. The observations were not
simultaneous. The Suzaku and INTEGRAL broad band energy coverage allows us to
constrain the spectral shape of the continuum emission well. We use the model
already proposed for this source, consisting of a Comptonised component
absorbed by interstellar matter and partially absorbed by local neutral matter,
and we added a Gaussian feature in absorption at keV. This addition
significantly improves the fit and flattens the residuals between 0.6 and 0.8
keV. We interpret the Gaussian feature in absorption as a cyclotron resonant
scattering feature (CRSF) produced close to the neutron star surface and derive
the magnetic field strength at the surface of the neutron star, G for a radius of 10 km. We derive the pulse period in the
EPIC-pn data to be 0.5928850(6) s and estimate that the spin period derivative
of X1822-371 is s/s using all available
pulse period measurements. Assuming that the intrinsic luminosity of
X1822-371is at the Eddington limit and using the values of spin period and spin
period derivative of the source, we constrain the neutron star and companion
star masses. We find the neutron star and the companion star masses to be M and M, respectively, for a
neutron star radius of 10 km.In a self-consistent scenario in which X1822-371
is spinning-up and accretes at the Eddington limit, we estimate that the
magnetic field of the neutron star is G for a
neutron star radius of 10 km. If our interpretation is correct, the Gaussian
absorption feature near 0.7 keV is the very first detection of a CRSF below 1
keV in a LMXB. (abridged)Comment: 14 pages, 12 figures, accepted for publication in A&
An XMM-Newton and INTEGRAL view on the hard state of EXO 1745-248 during its 2015 outburst
CONTEXT - Transient low-mass X-ray binaries (LMXBs) often show outbursts
lasting typically a few-weeks and characterized by a high X-ray luminosity
( erg/sec), while for most of the time they are
found in X-ray quiescence ( erg/sec). EXO 1745-248
is one of them. AIMS - The broad-band coverage, and the sensitivity of
instrument on board of {\xmm} and {\igr}, offers the opportunity to
characterize the hard X-ray spectrum during {\exo} outburst. METHODS - In this
paper we report on quasi-simultaneous {\xmm} and {\igr} observations of the
X-ray transient {\exo} located in the globular cluster Terzan 5, performed ten
days after the beginning of the outburst (on 2015 March 16th) shown by the
source between March and June 2015. The source was caught in a hard state,
emitting a 0.8-100 keV luminosity of ~{\lumcgs}. RESULTS - The
spectral continuum was dominated by thermal Comptonization of seed photons with
temperature keV, by a cloud with moderate optical depth
and electron temperature keV. A weaker soft
thermal component at temperature --0.7 keV and compatible
with a fraction of the neutron star radius was also detected. A rich emission
line spectrum was observed by the EPIC-pn on-board {\xmm}; features at energies
compatible with K- transitions of ionized sulfur, argon, calcium and
iron were detected, with a broadness compatible with either thermal Compton
broadening or Doppler broadening in the inner parts of an accretion disk
truncated at gravitational radii from the neutron star. Strikingly, at
least one narrow emission line ascribed to neutral or mildly ionized iron is
needed to model the prominent emission complex detected between 5.5 and 7.5
keV. (Abridged)Comment: 14 pages, 6 figure, 2 tables. Accepted for publication on A&A
(21/03/2017
GRO J1744-28: an intermediate B-field pulsar in a low mass X-ray binary
The bursting pulsar, GRO J1744-28, went again in outburst after 18
years of quiescence in mid-January 2014. We studied the broad-band, persistent,
X-ray spectrum using X-ray data from a XMM-Newton observation, performed almost
at the peak of the outburst, and from a close INTEGRAL observation, performed 3
days later, thus covering the 1.3-70.0 keV band. The spectrum shows a complex
continuum shape that cannot be modelled with standard high-mass X-ray pulsar
models, nor by two-components models. We observe broadband and peaked residuals
from 4 to 15 keV, and we propose a self-consistent interpretation of these
residuals, assuming they are produced by cyclotron absorption features and by a
moderately smeared, highly ionized, reflection component. We identify the
cyclotron fundamental at 4.7 keV, with hints for two possible harmonics
at 10.4 keV and 15.8 keV. The position of the cyclotron fundamental allows an
estimate for the pulsar magnetic field of (5.27 0.06) 10
G, if the feature is produced at its surface. From the dynamical and
relativistic smearing of the disk reflected component, we obtain a lower limit
estimate for the truncated accretion disk inner radius, ( 100 R),
and for the inclination angle (18-48). We also detect the
presence of a softer thermal component, that we associate with the emission
from an accretion disk truncated at a distance from the pulsar of 50-115 R.
From these estimates, we derive the magneto-spheric radius for disk accretion
to be 0.2 times the classical Alfv\'en radius for radial accretion.Comment: Accepted for publication in MNRA
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