1,952 research outputs found
The resolved fraction of the Cosmic X-ray Background
We present the X-ray source number counts in two energy bands (0.5-2 and 2-10
keV) from a very large source sample: we combine data of six different surveys,
both shallow wide field and deep pencil beam, performed with three different
satellites (ROSAT, Chandra and XMM-Newton). The sample covers with good
statistics the largest possible flux range so far: [2.4*10^-17 - 10^-11] cgs in
the soft band and [2.1*10^-16 - 8*10^{-12}]cgs in the hard band. Integrating
the flux distributions over this range and taking into account the (small)
contribution of the brightest sources we derive the flux density generated by
discrete sources in both bands. After a critical review of the literature
values of the total Cosmic X--Ray Background (CXB) we conclude that, with the
present data, the 94.3%, and 88.8% of the soft and hard CXB can be ascribed to
discrete source emission. If we extrapolate the analytical form of the Log
N--Log S distribution beyond the flux limit of our catalog in the soft band we
find that the flux from discrete sources at ~3*10^-18 cgs is consistent with
the entire CXB, whereas in the hard band it accounts for only 93% of the total
CXB at most, hinting for a faint and obscured population to arise at even
fainter fluxes.Comment: Accepted for publication in Ap
Chandra detection of the radio and optical double hot spot of 3C 351
In this letter we report a Chandra X-ray detection of the double northern hot
spot of the radio quasar 3C 351. The hot spot has also been observed in the
optical with the Hubble Space Telescope (R-band) and with the 3.5m. Telescopio
Nazionale Galileo (B-band). The radio-to-optical and X-ray spectra are
interpreted as the results of the synchrotron and synchrotron-self-Compton
(SSC) mechanisms, respectively, with hot-spot magnetic field strengths ~3 times
smaller than the equipartition values. In the framework of shock acceleration
theory, we show that the requirement for such a relatively small field strength
is in agreement with the fitted synchrotron spectral models and with the sizes
of the hot spots. Finally, we show that the combination of a lower magnetic
field strength with the high frequencies of the synchrotron cut-off in the
fitted synchrotron spectra provides strong evidence for electron acceleration
in the hot spots.Comment: 16 pag. + 2 .PS figures (fig.2 color), ApJ Letter in pres
The deepest X-ray look at the Universe
The origin of the X-ray background, in particular at hard (2-10 keV)
energies, has been a debated issue for more than 30 years. The Chandra deep
fields provide the deepest look at the X-ray sky and are the best dataset to
study the X-ray background. We searched the Chandra Deep Field South for X-ray
sources with the aid of a dedicated wavelet-based algorithm. We are able to
reconstruct the Log N-Log S source distribution in the soft (0.5-2 keV) and
hard (2-10 keV) bands down to limiting fluxes of 2x10^{-17} erg s^{-1} cm^{-2}
and 2x10^{-16} erg s^{-1} cm^{-2}, respectively. These are a factor ~5 deeper
than previous investigations. We find that the soft relation continues along
the extrapolation from higher fluxes, almost completely accounting for the soft
X-ray background. On the contrary, the hard distribution shows a flattening
below ~2x10^{-14} erg s^{-1} cm^{-2}. Nevertheless, we can account for >68% of
the hard X-ray background, with the main uncertainty being the sky flux itself.Comment: Accepted for publication on ApJL. Two figures, requires emulateapj5
(included
Investigación arqueométrica de los ladrillos de las antiguas murallas defensivas de la ciudad de Pavía (norte de Italia)
A study was conducted on bricks sampled from the defense walls around the historic town of Pavia (northern Italy) erected during Roman (uncertain) and “Spanish”(sixteenth-seventeenth centuries) times. An analysis of colour, macro- and micro-chemical composition,mineralogical clusters and structural-textural features showed that similar raw materials were used in the manufacture of these bricks, although certain variations were identified: particle size is finer in Roman bricks, while the “Spanish” version contains ground carbonate and “chamotte” additives. The “Spanish” bricks,fired at lower temperatures, are more porous. The wide range of firing temperatures used to make “Spanish” bricks was very likely related to the intended use. The sporadic presence of maghemite is discussed in the context of the atmosphere prevailing in the kilns. The “Spanish” bricks are lighter in colour as a result of their carbonate content and lower firing temperature. These characteristics, which affect the weather resistance of the different types of brick, should be taken into account in restoration work.Se investigan ladrillos recogidos en las murallas defensivas de la histórica ciudad de Pavía (norte de Italia), que fueron construidas en tiempos romanos (no establecidos)y “españoles” (siglos XVI y XVII).En base al color, composición química tanto total como puntual, asociaciones mineralógicas y características texturales,se concluye que se utilizó una materia prima similar en ambas épocas, con algunas particularidades: granulometría más fina en los romanos, adición de carbonato molido y chamota en los “españoles”. Por su parte, la porosidad es mayor en los ladrillos “españoles”. El amplio rango de temperaturas de cocción observado para estos últimos debe estar relacionado con los distintos usos para los cuales fueron destinados. La presencia esporádica de maghemita se discute, además, en función del tipo de atmósfera imperante en el horno de cocción. El color de los ladrillos “españoles” es más claro, como corresponde a su mayor contenido en carbonatos y menor temperatura de cocción. Estas características ejercen una notable influencia en la resistencia a la meteorización de los distintos tipos de ladrillos y deben, ser tenidas en cuenta ala hora de elaborar posibles planes de restauración
Spotlight on Cardiovascular Scoring Systems in Covid-19: Severity Correlations in Real-world Setting
Objectives and Methods: the current understanding of the interplay between cardiovascular (CV) risk and Covid-19 is grossly inadequate. CV risk-prediction models are used to identify and treat high risk populations and to communicate risk effectively. These tools are unexplored in Covid-19. The main objective is to evaluate the association between CV scoring systems and chest X ray (CXR) examination (in terms of severity of lung involvement) in 50 Italian Covid-19 patients. Results only the Framingham Risk Score (FRS) was applicable to all patients. The Atherosclerotic Cardiovascular Disease Score (ASCVD) was applicable to half. 62% of patients were classified as high risk according to FRS and 41% according to ASCVD. Patients who died had all a higher FRS compared to survivors. They were all hypertensive. FRS≥30 patients had a 9.7 higher probability of dying compared to patients with a lower FRS. We found a strong correlation between CXR severity and FRS and ASCVD (P < 0.001). High CV risk patients had consolidations more frequently. CXR severity was significantly associated with hypertension and diabetes. 71% of hypertensive patients’ CXR and 88% of diabetic patients’ CXR had consolidations. Patients with diabetes or hypertension had 8 times greater risk of having consolidations. Conclusions: High CV risk correlates with more severe CXR pattern and death. Diabetes and hypertension are associated with more severe CXR. FRS offers more predictive utility and fits best to our cohort. These findings may have implications for clinical practice and for the identification of high-risk groups to be targeted for the vaccine precedence
The First INTEGRAL AGN Catalog
We present the first INTEGRAL AGN catalog, based on observations performed
from launch of the mission in October 2002 until January 2004. The catalog
includes 42 AGN, of which 10 are Seyfert 1, 17 are Seyfert 2, and 9 are
intermediate Seyfert 1.5. The fraction of blazars is rather small with 5
detected objects, and only one galaxy cluster and no star-burst galaxies have
been detected so far. A complete subset consists of 32 AGN with a significance
limit of 7 sigma in the INTEGRAL/ISGRI 20-40 keV data. Although the sample is
not flux limited, the distribution of sources shows a ratio of obscured to
unobscured AGN of 1.5 - 2.0, consistent with luminosity dependent unified
models for AGN. Only four Compton-thick AGN are found in the sample. Based on
the INTEGRAL data presented here, the Seyfert 2 spectra are slightly harder
(Gamma = 1.95 +- 0.01) than Seyfert 1.5 (Gamma = 2.10 +- 0.02) and Seyfert 1
(Gamma = 2.11 +- 0.05).Comment: 17 pages, 12 figures, accepted for publication in Ap
Suzaku Observations of the Circinus galaxy
We report Suzaku observations of the active, Compton-thick Circinus galaxy.
Observations were obtained with both the X-ray Imaging spectrometer (XIS) and
the Hard X-ray Detector (HXD). Below 10 keV, the nuclear spectrum is dominated
by radiation reflected from cold dense gas of high column density, while above
13 keV the radiation is directly transmitted nuclear emission seen through a
column density of $~ 4 x 10^{24} cm^-2. In the 0.2--10 keV band, the XIS
spectrum is contaminated at 5% level by the brightest off-nuclear source in
Circinus (CG X-1), but drops to 1% in the 5-10 keV and is negligible at higher
energies. We find no significant evidence for variability in the hard (>12 keV)
emission. The Circinus is marginally detected with the HXD/GSO in the 50--100
keV band at 2.5\sigma level. We model the 3-70 keV band XIS+PIN spectra with a
four components: the Compton transmitted nuclear emission, the reflected
nuclear emission, a soft power law (representing a combination of scattered
nuclear emission, extended emission and contamination by sources in the galaxy
below a few keV). The hard nuclear power-law is found to have a photon index
Gamma_h ~= 1.6, very similar to the soft power-law. The high energy cut-off is
E_C ~= 49 keV. These results agree with those from BeppoSax. An extrapolation
of this model up to the GSO band shows good agreement with the GSO spectrum and
supports our detection of the Circinus up to ~= 100keV.Comment: ApJ accepte
A large population of mid-infrared selected, obscured active galaxies in the Bootes field
We identify a population of 640 obscured and 839 unobscured AGNs at redshifts
0.7<z<~3 using multiwavelength observations of the 9 deg^2 NOAO Deep Wide-Field
Survey (NDWFS) region in Bootes. We select AGNs on the basis of Spitzer IRAC
colors obtained by the IRAC Shallow Survey. Redshifts are obtained from optical
spectroscopy or photometric redshift estimators. We classify the IR-selected
AGNs as IRAGN 1 (unobscured) and IRAGN 2 (obscured) using a simple criterion
based on the observed optical to mid-IR color, with a selection boundary of
R-[4.5]=6.1, where R and [4.5] are the Vega magnitudes in the R and IRAC 4.5
micron bands, respectively. We verify this selection using X-ray stacking
analyses with data from the Chandra XBootes survey, as well as optical
photometry from NDWFS and spectroscopy from MMT/AGES. We show that (1) these
sources are indeed AGNs, and (2) the optical/IR color selection separates
obscured sources (with average N_H~3x10^22 cm^-2 obtained from X-ray hardness
ratios, and optical colors and morphologies typical of galaxies) and unobscured
sources (with no X-ray absorption, and quasar colors and morphologies), with a
reliability of >~80%. The observed numbers of IRAGNs are comparable to
predictions from previous X-ray, optical, and IR luminosity functions, for the
given redshifts and IRAC flux limits. We observe a bimodal distribution in
R-[4.5] color, suggesting that luminous IR-selected AGNs have either low or
significant dust extinction, which may have implications for models of AGN
obscuration.Comment: 23 emulateapj pages, 24 figures, 4 tables, v2: minor changes match
version to appear in Ap
The Canada-UK Deep Submillimetre Survey: The Survey of the 14-hour field
We have used SCUBA to survey an area of 50 square arcmin, detecting 19
sources down to a 3sigma sensitivity limit of 3.5 mJy at 850 microns. We have
used Monte-Carlo simulations to assess the effect of source confusion and noise
on the SCUBA fluxes and positions, finding that the fluxes of sources in the
SCUBA surveys are significantly biased upwards and that the fraction of the 850
micron background that has been resolved by SCUBA has been overestimated. The
radio/submillmetre flux ratios imply that the dust in these galaxies is being
heated by young stars rather than AGN. We have used simple evolution models
based on our parallel SCUBA survey of the local universe to address the major
questions about the SCUBA sources: (1) what fraction of the star formation at
high redshift is hidden by dust? (2) Does the submillimetre luminosity density
reach a maximum at some redshift? (3) If the SCUBA sources are
proto-ellipticals, when exactly did ellipticals form? However, we show that the
observations are not yet good enough for definitive answers to these questions.
There are, for example, acceptable models in which 10 times as much
high-redshift star formation is hidden by dust as is seen at optical
wavelengths, but also acceptable ones in which the amount of hidden star
formation is less than that seen optically. There are acceptable models in
which very little star formation occurred before a redshift of three (as might
be expected in models of hierarchical galaxy formation), but also ones in which
30% of the stars have formed by this redshift. The key to answering these
questions are measurements of the dust temperatures and redshifts of the SCUBA
sources.Comment: 41 pages (latex), 17 postscript figures, to appear in the November
issue of the Astronomical Journa
- …