1,384 research outputs found
Spectral variability in Cygnus X-3
We model the broad-band X-ray spectrum of Cyg X-3 in all states displayed by
this source as observed by the Rossi X-ray Timing Explorer. From our models, we
derive for the first time unabsorbed spectral shapes and luminosities for the
full range of spectral states. We interpret the unabsorbed spectra in terms of
Comptonization by a hybrid electron distribution and strong Compton reflection.
We study the spectral evolution and compare with other black hole as well as
neutron star sources. We show that a neutron star accretor is not consistent
with the spectral evolution as a function of Ledd and especially not with the
transition to a hard state. Our results point to the compact object in Cyg X-3
being a massive, ~30 Msun black hole.Comment: 14 pages, 9 figures, accepted for publication in MNRA
An adaptive-binning method for generating constant-uncertainty/constant-significance light curves with Fermi-LAT data
We present a method enabling the creation of
constant-uncertainty/constant-significance light curves with the data of the
Fermi-Large Area Telescope (LAT). The adaptive-binning method enables more
information to be encapsulated within the light curve than with the
fixed-binning method. Although primarily developed for blazar studies, it can
be applied to any sources. This method allows the starting and ending times of
each interval to be calculated in a simple and quick way during a first step.
The reported mean flux and spectral index (assuming the spectrum is a power-law
distribution) in the interval are calculated via the standard LAT analysis
during a second step. The absence of major caveats associated with this method
has been established by means of Monte-Carlo simulations. We present the
performance of this method in determining duty cycles as well as power-density
spectra relative to the traditional fixed-binning method.Comment: 17 pages, 13 figures, 5 tables. Submitted to A&
Adherence in Rheumatoid Arthritis patients assessed with a validated Italian version of the 5-item compliance questionnaire for rheumatology
OBJECTIVES: The 5-item Compliance Questionnaire for Rheumatology (CQR5) proved reliability and validity in respect of identification of patients likely to be high adherers (HAs) to anti-rheumatic treatment, or low adherers (LAs), i.e. taking<80% of their medications correctly. The objective of the study was to validate an Italian version of CQR5 (I-CQR5) in rheumatoid arthritis (RA) patients and to investigate factors associated with high adherence. METHODS: RA patients, undergoing treatment with ≥1 self-administered conventional synthetic disease-modifying anti-rheumatic drug (csDMARD) or biological DMARD (bDMARD), were enrolled. The cross-cultural adaptation and validation of I-CQR5 followed standardised guidelines. I-CQR5 was completed by patients on one occasion. Data were subjected to factor analysis and Partial Credit model Parametrisation (PCM) to assess construct validity of I-CQR5. Analysis of factors associated with high adherence included demographic, social, clinical and treatment information. Factors achieving a p<0.10 in univariate analysis were included in multivariable analysis. RESULTS: Among 604 RA patients, 274 patients were included in the validation and 328 in the analysis of factors associated with adherence. Factor analysis and PCM confirmed the construct validity and consistency of I-CQR5. HAs were found to be 109 (35.2%) of the patients. bDMARD treatment and employment were found to be independently associated with high adherence: OR 2.88 (1.36-6.1), p=0.006 and OR 2.36 (1.21-4.62), p=0.012, respectively. CONCLUSIONS: Only one-third of RA patients were HAs according to I-CQR5. bDMARDs and employment status increased by almost 3-fold the likelihood of being highly adherent to the anti-rheumatic treatment.Peer reviewe
Hard X-ray colours of Neutron Star and Black Hole Low Mass X-ray Binaries with INTEGRAL
The X-ray spectra of Low Mass X-ray Binaries (LMXB) can change on short
time-scales, making it difficult to follow their spectral characteristics in
detail through model fitting. Colour-colour (C-C) diagrams are therefore often
used as alternative, model independent, tools to study the spectral variability
of these sources. The INTEGRAL mission, with its high sensitivity, large field
of view and good angular resolution, is well suited to study the hard X-ray
properties of LMXBs. In particular the ISGRI imager on board of INTEGRAL allows
the regular monitoring of the sources in the less frequently studied domain
above 20 keV. In this proceeding, C-C diagrams have been made with data from
the INTEGRAL public archive; a search is made for systematic differences in the
C-C diagrams between black hole candidates (BH) and neutron stars (NS) in LMXBs
using a moments analysis method.Comment: Paper from poster presentation at COSPAR meeting, Beijing, 2006. in
press: Advances in Space Research, Editor: Wynn H
Let Me Introduce You to a New PEER: The Postsecondary Education, Employment, and Research Project at USU
The broad-band X-ray spectrum of the dipping Low Mass X-ray Binary EXO0748--676
We present results of a 0.1-100 keV BeppoSAX observation of the dipping LMXRB
EXO 0748-676 performed in 2000 November. During the observation the source
exhibited X-ray eclipses, type I X-ray bursts and dipping activity over a wide
range of orbital phases. The 0.1-100keV "dip-free"(ie. dipping and eclipsing
intervals excluded) spectrum is complex,especially at low-energies where a soft
excess is present. Two very different spectral models give satisfactory fits.
The first is the progressive covering model, consisting of separately absorbed
black body and cut-off power-law components.The second model is an absorbed
cut-off power-law together with a moderately ionized absorber with a sub-solar
abundance of Fe and a 2.13 keV absorption feature (tentatively identified with
Si xiii). This ionized absorber may be the same feature as seen by Chandra
during dips from EXO 0748-676.Comment: 7 pages, 5 figures, paper accepted for publication in Astronomy and
Astrophysic
Ionized Absorbers in AGN: the Role of Collisional Ionization and Time-Evolving Photoionization
In this paper we explore collisional ionization and time-evolving
photoionization in the, X-ray discovered, ionized absorbers in Seyfert
galaxies. These absorbers show temporal changes inconsistent with simple
equilibrium models. We develop a simple code to follow the temporal evolution
of non-equilibrium photoionized gas. As a result several effects appear that
are easily observable; and which, in fact, may explain otherwise paradoxical
behavior.
Specifically we find that: 1) In many important astrophysical conditions pure
collisional and photoionization equilibria can be distinguished with moderate
spectral resolution observations, due to a strong absorption structure between
1 and 3 keV. 2) In time-evolving non-equilibrium photoionization models the
response of the ionization state of the gas to sudden changes of the ionizing
continuum is smoothed and delayed at low gas densities, even when the
luminosity increases. 3) If the changes of the ionizing luminosity are not
instantaneous, and the electron density is low enough (the limit depends on the
average ionization state of the gas), the ionization state of the gas can
continue to increase while the source luminosity decreases, so a maximum in the
ionization state of a given element may occur during a minimum of the ionizing
intensity (the opposite of the prediction of equilibrium models). 4) Different
ions of different elements reach their equilibrium configuration on different
time-scales.
These properties are similar to those seen in several ionized absorbers in
AGN, properties which had hitherto been puzzling. We applied these models to a
high S/N ROSAT PSPC observation of the Seyfert 1 galaxy NGC 4051.Comment: 36 pages, 10 figures, accepted for publication on Apj, in pres
High Energy Break and Reflection Features in the Seyfert Galaxy MCG+8-11-11
We present the results from ASCA and OSSE simultaneous observations of the
Seyfert 1.5 galaxy MCG+8-11-11 performed in August-September 1995. The ASCA
observations indicate a modest flux increase (20%) in 3 days, possibly
correlated to a softening of the 0.6-9 keV spectrum. The spectrum is well
described by a hard power law (Gamma=1.64) absorbed by a column density
slightly larger than the Galactic value, with an iron line at 6.4 keV of EW=400
eV. The simultaneous OSSE data are characterized by a much softer power law
with photon index Gamma=3.0, strongly suggesting the presence of a spectral
break in the hard X/soft gamma-ray band. A joint fit to OSSE and ASCA data
clearly shows an exponential cut-off at about 300 keV, and strong reflection
component. MCG+8-11-11 features a spectral break in the underlying continuum
unambiguously. This, together with the inferred low compactness of this source,
favours thermal or quasi-thermal electron Comptonization in a structured Corona
as the leading process of high energy radiation production.Comment: 13 pages, + 4 figure.ps AAS LateX [11pt,aasms4]{article} To be
published in ApJ, Main Journa
A burst from the direction of UZ Fornacis with XMM-Newton
The XMM-Newton pointing towards the magnetic cataclysmic variable UZ For
finds the source to be a factor > 10^3 fainter than previous EXOSAT and ROSAT
observations. The source was not detected for the majority of a 22 ksec
exposure with the EPIC cameras, suggesting that the accretion rate either
decreased, or stopped altogether. However a 1.1 ksec burst was detected from UZ
For during the observation. Spectral fits favour optically thin, kT = 4.4 keV
thermal emission. Detection of the burst by the on-board Optical Monitor
indicates that this was most probably an accretion event. The 0.1-10 keV
luminosity of 2.1 x 10^30 erg/s is typical for accretion shock emission from
high state polars and would result from the potential energy release of ~ 10^16
g of gas. There is no significant soft excess due to reprocessing in the white
dwarf atmosphere.Comment: 7 pages, 2 postscript figures, ApJL, in pres
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