87 research outputs found
Nonthermal hard X-ray excess in the Coma cluster: resolving the discrepancy between the results of different PDS data analyses
The detection of a nonthermal excess in the Coma cluster spectrum by two
BeppoSAX observations analyzed with the XAS package (Fusco-Femiano et al.) has
been disavowed by an analysis (Rossetti & Molendi) performed with a different
software package (SAXDAS) for the extraction of the spectrum. To resolve this
discrepancy we reanalyze the PDS data considering the same software used by
Rossetti & Molendi. A correct selection of the data and the exclusion of
contaminating sources in the background determination show that also the SAXDAS
analysis reports a nonthermal excess with respect to the thermal emission at
about the same confidence level of that obtained with the XAS package
(~4.8sigma). Besides, we report the lack of the systematic errors investigated
by Rossetti & Molendi and Nevalainen et al. taking into account the whole
sample of the PDS observations off the Galactic plane, as already shown in our
data analysis of Abell 2256 (Fusco-Femiano, Landi & Orlandini). All this
eliminates any ambiguity and confirms the presence of a hard tail in the
spectrum of the Coma cluster.Comment: 12 pages, 2 figures. Accepted for publication in ApJ Letter
Broad band time-resolved E_{p,i}--L_{iso} correlation in GRBs
We report results of a systematic study of the broad band (2--2000 keV) time
resolved prompt emission spectra of a sample of gamma-ray bursts (GRBs)
detected with both Wide Field Cameras on board the \sax\ satellite and the
\batse\ experiment on board CGRO. In this first paper, we study the
time-resolved dependence of the intrinsic peak energy of the
spectrum on the corresponding isotropic bolometric luminosity .
The -- relation or the equivalent relation between
and the bolometric released energy , derived using the time
averaged spectra of long GRBs with known redshift, is well established, but its
physical origin is still a subject of discussion. In addition, some authors
maintain that these relations are the result of instrumental selection effects.
We find that not only a relation between the measured peak energy and the
corresponding energy flux, but also a strong versus
correlation are found within each burst and merging together the time resolved
data points from different GRBs. We do not expect significant instrumental
selection effects that can affect the obtained results, apart from the fact
that the GRBs in our sample are sufficiently bright to perform a time-resolved
spectroscopy and that they have known redshift. If the fundamental physical
process that gives rise to the GRB phenomenon does not depend on its
brightness, we conclude that the found versus
correlation within each GRB is intrinsic to the emission process, and that the
correlations discovered by Amati et al. and Yonetoku et al. are likely not the
result of selection effects. We also discuss the properties of the correlations
found.Comment: 27 pages,4 tables, 7 figure, accepted for publication in The
Astrophysical Journa
Flat-spectrum radio sources as likely counterparts of unidentified INTEGRAL sources (Research Note)
Many sources in the fourth INTEGRAL/IBIS catalogue are still unidentified,
since they lack an optical counterpart. An important tool that can help in
identifying/classifying these sources is the cross-correlation with radio
catalogues, which are very sensitive and positionally accurate. Moreover, the
radio properties of a source, such as the spectrum or morphology, could provide
further insight into its nature. Flat-spectrum radio sources at high Galactic
latitudes are likely to be AGN, possibly associated to a blazar or to the
compact core of a radio galaxy. Here we present a small sample of 6 sources
extracted from the fourth INTEGRAL/IBIS catalogue that are still
unidentified/unclassified, but which are very likely associated with a bright,
flat-spectrum radio object. To confirm the association and to study the source
X-ray spectral parameters, we performed X-ray follow-up observations with
Swift/XRT. We report the results obtained from this search and discuss the
nature of each source. 5 of the 6 radio associations are also detected in
X-rays; in 3 cases they are the only counterpart found. IGR J06073--0024 is a
flat-spectrum radio quasar at z=1.08, IGR J14488--4008 is a newly discovered
radio galaxy, while IGR J18129--0649 is an AGN of a still unknown type. The
nature of IGR J07225--3810 and IGR J19386--4653 is less well defined, since in
both cases we find another X-ray source in the INTEGRAL error circle;
nevertheless, the flat-spectrum radio source, likely to be a radio loud AGN,
remains a viable and more convincing association in both cases. Only for IGR
J11544--7618 could we not find any convincing counterpart since the radio
association is not an X-ray emitter.Comment: 7 pages, 7 figures, accepted for publication on Astronomy and
Astrophysic
Nonthermal hard X-ray excess in the cluster Abell 2256 from two epoch observations
After confirmation of the presence of a nonthermal hard X-ray excess with
respect to the thermal emission in the Coma cluster from two independent
observations, obtained using the Phoswich Detection System onboard BeppoSAX, we
present in this Letter also for Abell 2256 the results of two observations
performed with a time interval of about 2.5 yr. In both spectra a nonthermal
excess is present at a confidence level of ~3.3sigma and ~3.7sigma,
respectively. The combined spectrum obtained by adding up the two spectra
allows to measure an excess at the level of ~4.8sigma in the 20-80 keV energy
range. The nonthermal X-ray flux is in agreement with the published value of
the first observation (Fusco-Femiano et al. 2000) and with that measured by a
Rossi X-Ray Timing Explorer observation (Rephaeli & Gruber 2003).Comment: 12 pages, 3 figures, 1 table - ApJL, in pres
The cosmic X-ray background and the population of the most heavily obscured AGNs
We report on an accurate measurement of the CXB in the 15-50 keV range
performed with the Phoswich Detection System (PDS) instrument aboard the
BeppoSAX satellite. We establish that the most likely CXB intensity level at
its emission peak (26-28 keV) is ~40 keV/cm2/s/sr, a value consistent with that
derived from the best available CXB measurement obtained over 25 years ago with
the first High Energy Astronomical Observatory satellite mission (HEAO-1;
Gruber et al. 1999), whose intensity, lying well below the extrapolation of
some lower energy measurements performed with focusing telescopes, was
questioned in the recent years. We find that 90% of the acceptable solutions of
our best fit model to the PDS data give a 20-50 keV CXB flux lower than 6.5E-08
erg/cm2/s/sr, which is 12% higher than that quoted by Gruber et al. (1999) when
we use our best calibration scale. This scale gives a 20-50 keV flux of the
Crab Nebula of 9.22E-09 erg/cm2/s, which is in excellent agreement with the
most recent Crab Nebula measurements and 6% smaller than that assumed by Gruber
et al. (1999). In combination with the CXB synthesis models we infer that about
25% of the intensity at ~30 keV arises from extremely obscured, Compton thick
AGNs (absorbing column density N_H > 1.0E+24 H/cm2), while a much larger
population would be implied by the highest intensity estimates. We also infer a
mass density of supermassive BHs of ~3.0E+05 Msol/Mpc3. The summed contribution
of resolved sources (Moretti et al. 2003) in the 2-10 keV band exceeds our best
fit CXB intensity extrapolated to lower energies, but it is within our upper
limit, so that any significant contribution to the CXB from sources other than
AGNs, such as star forming galaxies and diffuse Warm-Hot Intergalactic Medium
(WHIM), is expected to be mainly confined below a few keV.Comment: Accepted for publication in ApJ Main: 30 pages, 3 Tables, 8 Figures.
Many revisions due to the change of the Journa
Baseline Plasma Gas6 Protein Elevation Predicts Adverse Outcomes in Hospitalized COVID-19 Patients
: Reliable biomarkers allowing early patients' stratification for the risk of adverse outcomes in COVID-19 are lacking. Gas6, together with its tyrosine kinase receptors named TAM, is involved in the regulation of immune homeostasis, fibrosis, and thrombosis. Our aim was to evaluate whether Gas6, sAxl, and sMerTK could represent early predictors of disease evolution either towards a negative (death or need of ICU admission) or a positive (discharge and/or clinical resolution within the first 14 days of hospitalization) outcome. To this purpose, between January and May 2021 (corresponding to third pandemic wave in Italy), 139 consecutive SARS-CoV-2 positive patients were enrolled in a prospective observational study. Plasma levels of these molecules were measured by ELISA at the time of hospitalization and after 7 and 14 days. We observed that higher plasma Gas6 concentrations at hospital admission were associated with a worsening in clinical conditions while lower sMerTK concentrations at baseline and after 7 days of hospitalization were associated with a more favorable outcome. At multivariate analysis, after correction for demographic and COVID-19 severity variables (NEWS2 and PiO2/FiO2), only Gas6 measured at baseline predicted an adverse prognosis with an odds ratio of 1.03 (C.I. 1.01-10.5). At ROC curve analysis, baseline Gas6 levels higher than 58.0 ng/ml predicted a severe disease evolution with 53.3% sensitivity and 77.6% specificity (area under the curve 0.653, p = 0.01, likelihood ratio of 2.38, IQR: 1.46-3.87). Taken together, these results support the hypothesis that a dysregulation in the Gas6/TAM axis could play a relevant role in modulating the course of COVID-19 and suggest that plasma Gas6 may represent a promising prognostic laboratory parameter for this condition
Measuring the cosmological parameters with the Ep,i-Eiso correlation of Gamma-Ray Bursts
We have used the Ep,i-Eiso correlation of GRBs to measure the cosmological
parameter Omega_M. By adopting a maximum likelihood approach which allows us to
correctly quantify the extrinsic (i.e. non--Poissonian) scatter of the
correlation, we constrain (for a flat universe) Omega_M to 0.04-0.40 (68%
confidence level), with a best fit value of Omega_M ~ 0.15, and exclude Omega_M
= 1 at 99.9% confidence level. If we release the assumption of a flat universe,
we still find evidence for a low value of Omega_M (0.04-0.50 at 68% confidence
level) and a weak dependence of the dispersion of the Ep,i-Eiso correlation on
Omega_Lambda (with an upper limit of Omega_Lambda ~ 1.15 at 90% confidence
level). Our approach makes no assumptions on the Ep,i-Eiso correlation and it
does not use other calibrators to set the "zero' point of the relation,
therefore our treatment of the data is not affected by circularity and the
results are independent of those derived via type Ia SNe (or other cosmological
probes). Unlike other multi-parameters correlations, our analysis grounds on
only two parameters, then including a larger number (a factor ~3) of GRBs and
being less affected by systematics. Simulations based on realistic
extrapolations of ongoing (and future) GRB experiments (e.g., Swift,
Konus-Wind, GLAST) show that: i) the uncertainties on cosmological parameters
can be significantly decreased; ii) future data will allow us to get clues on
the "dark energy" evolution.Comment: 9 pages, 12 figures, revised version, accepted for publication in
MNRA
Baseline Plasma Osteopontin Protein Elevation Predicts Adverse Outcomes in Hospitalized COVID-19 Patients
More than three years have passed since the first case, and COVID-19 is still a health concern, with several open issues such as the lack of reliable predictors of a patient's outcome. Osteopontin (OPN) is involved in inflammatory response to infection and in thrombosis driven by chronic inflammation, thus being a potential biomarker for COVID-19. The aim of the study was to evaluate OPN for predicting negative (death or need of ICU admission) or positive (discharge and/or clinical resolution within the first 14 days of hospitalization) outcome. We enrolled 133 hospitalized, moderate-to-severe COVID-19 patients in a prospective observational study between January and May 2021. Circulating OPN levels were measured by ELISA at admission and at day 7. The results showed a significant correlation between higher plasma concentrations of OPN at hospital admission and a worsening clinical condition. At multivariate analysis, after correction for demographic (age and gender) and variables of disease severity (NEWS2 and PiO2/FiO2), OPN measured at baseline predicted an adverse prognosis with an odds ratio of 1.01 (C.I. 1.0-1.01). At ROC curve analysis, baseline OPN levels higher than 437 ng/mL predicted a severe disease evolution with 53% sensitivity and 83% specificity (area under the curve 0.649, p = 0.011, likelihood ratio of 1.76, (95% confidence interval (CI): 1.35-2.28)). Our data show that OPN levels determined at the admission to hospital wards might represent a promising biomarker for early stratification of patients' COVID-19 severity. Taken together, these results highlight the involvement of OPN in COVID-19 evolution, especially in dysregulated immune response conditions, and the possible use of OPN measurements as a prognostic tool in COVID-19
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