220 research outputs found
Is a Classical Language Adequate in Assessing the Detectability of the Redshifted 21cm Signal from the Early Universe?
The classical radiometer equation is commonly used to calculate the
detectability of the 21cm emission by diffuse cosmic hydrogen at high
redshifts. However, the classical description is only valid in the regime where
the occupation number of the photons in phase space is much larger than unity
and they collectively behave as a classical electromagnetic field. At redshifts
z<20, the spin temperature of the intergalactic gas is dictated by the
radiation from galaxies and the brightness temperature of the emitting gas is
in the range of mK, independently from the existence of the cosmic microwave
background. In regions where the observed brightness temperature of the 21cm
signal is smaller than the observed photon energy, of 68/(1+z) mK, the
occupation number of the signal photons is smaller than unity. Neverethless,
the radiometer equation can still be used in this regime because the weak
signal is accompanied by a flood of foreground photons with a high occupation
number (involving the synchrotron Galactic emission and the cosmic microwave
background). As the signal photons are not individually distinguishable, the
combined signal+foreground population of photons has a high occupation number,
thus justifying the use of the radiometer equation.Comment: 4 pages, Accepted for publication in JCA
A systematic approach to the Planck LFI end-to-end test and its application to the DPC Level 1 pipeline
The Level 1 of the Planck LFI Data Processing Centre (DPC) is devoted to the
handling of the scientific and housekeeping telemetry. It is a critical
component of the Planck ground segment which has to strictly commit to the
project schedule to be ready for the launch and flight operations. In order to
guarantee the quality necessary to achieve the objectives of the Planck
mission, the design and development of the Level 1 software has followed the
ESA Software Engineering Standards. A fundamental step in the software life
cycle is the Verification and Validation of the software. The purpose of this
work is to show an example of procedures, test development and analysis
successfully applied to a key software project of an ESA mission. We present
the end-to-end validation tests performed on the Level 1 of the LFI-DPC, by
detailing the methods used and the results obtained. Different approaches have
been used to test the scientific and housekeeping data processing. Scientific
data processing has been tested by injecting signals with known properties
directly into the acquisition electronics, in order to generate a test dataset
of real telemetry data and reproduce as much as possible nominal conditions.
For the HK telemetry processing, validation software have been developed to
inject known parameter values into a set of real housekeeping packets and
perform a comparison with the corresponding timelines generated by the Level 1.
With the proposed validation and verification procedure, where the on-board and
ground processing are viewed as a single pipeline, we demonstrated that the
scientific and housekeeping processing of the Planck-LFI raw data is correct
and meets the project requirements.Comment: 20 pages, 7 figures; this paper is part of the Prelaunch status LFI
papers published on JINST:
http://www.iop.org/EJ/journal/-page=extra.proc5/jins
On the Soft Excess in the X-ray Spectrum of Cir X-1: Revisitation of the Distance to Cir X-1
We report on a 300 ks BeppoSAX (0.12-200 keV) observation of Circinus X-1
(Cir X-1) at phases between 0.62 and 0.84 and on a 90 ks BeppoSAX observation
of Cir X--1 at phases 0.11-0.16. Using the canonical model adopted until now to
fit the energy spectrum of this source large residuals appear below 1 keV.
These are well fitted using an equivalent hydrogen column of cm, adding absorption edges of O VII, O VIII and Ne IX in the
spectra extracted from the observation at phases 0.62-0.84 and adding
absorption edges of O VII, O VIII, Mg XI and Mg XII and absorption lines of O
VIII and Mg XII in the spectra extracted from the observation at phases
0.11-0.16. During the observation at phases 0.62--0.84 the electron density
associated to the ionized matter is cm remaining quit
constant going away from the compact object. During the observation at phases
0.11-0.16 the electron density profile varies along the distance going from
cm at cm to cm at cm. The equivalent hydrogen column towards
Cir X-1 is thre times lower than the value obtained from previous models. This
low value would imply that Cir X-1 is at a distance of 4.1 kpc.Comment: 30 pages, 11 figures, accepted by Ap
Fundamental Properties and Distances of LMC Eclipsing Binaries: III. EROS 1044
We present results from a detailed analysis of a third eclipsing binary (EB)
system in the Large Magellanic Cloud, EROS 1044 (~B2 IV-V + ~B2 III-IV). Our
study combines the "classical" EB study of light and radial velocity curves
with detailed modeling of the observed spectral energy distribution, and yields
an essentially complete picture of the stellar properties of the system and a
determination of its distance. The observational data exploited include optical
photometry, space-based UV spectroscopy, and UV/optical spectrophotometry. The
advantages of our technique include numerous consistency checks and, in the
case of the distance determinations, the absence of zero point uncertainties
and adjustable parameters. We find the EROS 1044 system to consist of a pair of
normal, mildly-evolved ~21000 K stars, whose derived properties are consistent
with stellar evolution calculations. The distance to the system is 47.5+/-1.8
kpc. We discuss the implications of our results for three EB systems (HV 2274,
HV 982, and EROS 1044) on the general distance to the Large Magellanic Cloud.Comment: 18 pages, 8 figures, accepted for publication in Ap
Trends in incidence, mortality and survival in women with breast cancer from 1985 to 2012 in Granada, Spain: a population-based study
The incidence of breast cancer has increased since the 1970s. Despite favorable trends in prognosis,
the role of changes in clinical practice and the introduction of screening remain controversial. We examined breast
cancer trends to shed light on their determinants Overall, age-adjusted (European Standard Population) incidence rates increased from 48.0 cases × 100,000
women in 1985–1989 to 83.4 in 2008–2012, with an annual percentage change (APC) of 2.5% (95%CI, 2.1–2.9) for
1985–2012. The greatest increase was in women younger than 40 years (APC 3.5, 95%CI, 2.4–4.8). For 2000–2012
the incidence trend increased only for stage I tumors (APC 3.8, 95%CI, 1.9–5.8). Overall age-adjusted breast cancer
mortality decreased (APC − 1, 95%CI, − 1.4 – − 0.5), as did mortality in the 50–69 year age group (APC − 1.3, 95%CI,
− 2.2 – − 0.4). Age-standardized net survival increased from 67.5% at 5 years in 1985–1989 to 83.7% in 2010–2012.
All age groups younger than 70 years showed a similar evolution. Five-year net survival rates were 96.6% for
patients with tumors diagnosed in stage I, 88.2% for stage II, 62.5% for stage III and 23.3% for stage IV. Breast cancer incidence is increasing – a reflection of the evolution of risk factors and increasing
diagnostic pressure. After screening was introduced, the incidence of stage I tumors increased, with no decrease in
the incidence of more advanced stages. Reductions were seen for overall mortality and mortality in the 50–69 year
age group, but no changes were found after screening implementation. Survival trends have evolved favorably
except for the 70–84 year age group and for metastatic tumors.This study was supported by a grant from the Acción Estratégica en Salud
plan for the High Resolution Project on Prognosis and Care of Cancer
Patients (No. AC14/00036) awarded by the Spanish Ministry of Economy and
Competitiveness and co-funded by the European Regional Development
Fund (ERDF)
Radio emission from Supernova Remnants
The explosion of a supernova releases almost instantaneously about 10^51 ergs
of mechanic energy, changing irreversibly the physical and chemical properties
of large regions in the galaxies. The stellar ejecta, the nebula resulting from
the powerful shock waves, and sometimes a compact stellar remnant, constitute a
supernova remnant (SNR). They can radiate their energy across the whole
electromagnetic spectrum, but the great majority are radio sources. Almost 70
years after the first detection of radio emission coming from a SNR, great
progress has been achieved in the comprehension of their physical
characteristics and evolution. We review the present knowledge of different
aspects of radio remnants, focusing on sources of the Milky Way and the
Magellanic Clouds, where the SNRs can be spatially resolved. We present a brief
overview of theoretical background, analyze morphology and polarization
properties, and review and critical discuss different methods applied to
determine the radio spectrum and distances. The consequences of the interaction
between the SNR shocks and the surrounding medium are examined, including the
question of whether SNRs can trigger the formation of new stars. Cases of
multispectral comparison are presented. A section is devoted to reviewing
recent results of radio SNRs in the Magellanic Clouds, with particular emphasis
on the radio properties of SN 1987A, an ideal laboratory to investigate
dynamical evolution of an SNR in near real time. The review concludes with a
summary of issues on radio SNRs that deserve further study, and analyzing the
prospects for future research with the latest generation radio telescopes.Comment: Revised version. 48 pages, 15 figure
The Large Observatory for x-ray timing
The Large Observatory For x-ray Timing (LOFT) was studied within ESA M3 Cosmic Vision framework and participated in the final down-selection for a launch slot in 2022-2024. Thanks to the unprecedented combination of effective area and spectral resolution of its main instrument, LOFT will study the behaviour of matter under extreme conditions, such as the strong gravitational field in the innermost regions of accretion flows close to black holes and neutron stars, and the supra-nuclear densities in the interior of neutron stars. The science payload is based on a Large Area Detector (LAD, 10 m2 effective area, 2-30 keV, 240 eV spectral resolution, 1° collimated field of view) and a WideField Monitor (WFM, 2-50 keV, 4 steradian field of view, 1 arcmin source location accuracy, 300 eV spectral resolution). The WFM is equipped with an on-board system for bright events (e.g. GRB) localization. The trigger time and position of these events are broadcast to the ground within 30 s from discovery. In this paper we present the status of the mission at the end of its Phase A study
The LOFT mission concept: a status update
The Large Observatory For x-ray Timing (LOFT) is a mission concept which was proposed to ESA as M3 and M4 candidate in the framework of the Cosmic Vision 2015-2025 program. Thanks to the unprecedented combination of effective area and spectral resolution of its main instrument and the uniquely large field of view of its wide field monitor, LOFT will be able to study the behaviour of matter in extreme conditions such as the strong gravitational field in the innermost regions close to black holes and neutron stars and the supra-nuclear densities in the interiors of neutron stars. The science payload is based on a Large Area Detector (LAD, >8m2 effective area, 2-30 keV, 240 eV spectral resolution, 1 degree collimated field of view) and a Wide Field Monitor (WFM, 2-50 keV, 4 steradian field of view, 1 arcmin source location accuracy, 300 eV spectral resolution). The WFM is equipped with an on-board system for bright events (e.g., GRB) localization. The trigger time and position of these events are broadcast to the ground within 30 s from discovery. In this paper we present the current technical and programmatic status of the mission
- …