Search results for "X-Rays"
showing 10 items of 445 documents
Spectral Analysis of LMC-X2 with XMM/Newton
2008
We present the results of the analisys of an archival observation of LMC X-2 performed with XMM/Newton. The spectra of this source has never been analyzed with a high precision instrument before. The spectrum of the source can be fitted with a blackbody with a temperature 1.5 keV plus a disk blackbody at 0.8 keV. We argue that the emission of this source can be straightforwardly interpreted as a sum of the emission from a boundary layer between the NS and the disc and a blackbody component coming from the disc itself. The detection of the O VIII emission line (and the lack of detection of lines in the iron region) can be due to the fact that the source lies in the Large Magellanic Cloud.
Effects of radiation in accretion regions of classical T Tauri stars
2019
Context. Models and observations indicate that the impact of matter accreting onto the surface of young stars produces regions at the base of accretion columns where optically thin and thick plasma components coexist. Thus, an accurate description of these impacts is necessary to account for the effects of absorption and emission of radiation. Aims. We study the effects of radiation emerging from shock-heated plasma in impact regions on the structure of the pre-shock down-falling material. We investigate whether a significant absorption of radiation occurs and if it leads to a pre-shock heating of the accreting gas. Methods. We developed a radiation hydrodynamics model describing an accreti…
X-ray bursts and burst oscillations from the slowly spinning X-ray pulsar IGR J17480-2446 (Terzan 5)
2011
The newly discovered 11-Hz accreting pulsar, IGR J17480-2446, located in the globular cluster Terzan 5, has shown several bursts with a recurrence time as short as a few minutes. The source shows the shortest recurrence time ever observed from a neutron star. Here we present a study of the morphological, spectral and temporal properties of 107 bursts observed by the Rossi X-ray Timing Explorer. The recurrence time and the fluence of the bursts clearly anticorrelate with the increase in the persistent X-ray flux. The ratio between the energy generated by the accretion of mass and that liberated during bursts indicates that helium is ignited in a hydrogen-rich layer. Therefore, we conclude th…
Size of coronal structures in active stellar coronae from the detection of x-ray resonant scattering
2005
We have analyzed high-resolution X-ray spectra of a large sample of active stars observed with the High Energy Transmission Grating Spectrometer on Chandra in order to investigate the properties of optical thickness of the coronal plasma. The analysis of Lyman series lines arising from hydrogen-like oxygen and neon ions shows in the coronae of the active RS CVn-type binaries II Peg and IM Peg significant decrements in the Ly alpha/Ly beta ratios as compared with theoretical predictions and with the same ratios observed in similar active binaries. We interpret these depletions in terms of resonance scattering of line photons out of the line-of-sight. These observations present the first stro…
High Resolution X-ray Spectroscopy of Pre-Main-Sequence Stars: TWA 5 and PZ Tel
2004
We report on the analysis of high resolution X-ray spectra of two pre-main-sequence stars: TWA 5 (observed with XMM-Newton) and PZ Telescopii (observed with Chandra/HETGS). TWA 5 is a classical T Tauri star in the TW Hydrae association while PZ Tel is a rapidly rotating weak-lined T Tauri star in the beta-Pictoris moving group. For both stars we have reconstructed the emission measure distribution and derived the coronal abundances to check for possible patterns of the abundances related to the first ionization potential of the various elements. We have also derived estimates of the plasma density from the analysis of the He-like triplets. We compare the characteristics of our targets with …
Characterization of the ESR response of alanine dosimeters to low-energy (1-40 keV) X-rays
2016
The aminoacid L-a-alanine has attracted considerable interest for use in radiation ESR dosimetry and has been formally accepted as a secondary standard for high-dose (kGy) and transfer dosimetry . The accuracy of the method is quite high, largely due to the low dependence of the alanine response on various irradiation parameters (photon energies above 100 keV, dose rate, temperature, etc.). Furthermore, this system presents alinear response to dose, fairly high sensitivity, tissue equivalence, absence of fading, small dimensions, ruggedn ess, and non-destructive readout. In this work, we examined the energy dependence of alanine ESR dosimeters in the low energy X-photon energy range between…
DOES STILL EXIST A CORRELATION BETWEEN X-RAYS OCCUPATIONAL EXPOSURE AND BENIGN NODULAR THYROID DISEASE?
2019
Objective: The prevalence of benign nodular thyroid disease in the general population is high, as shown by various studies, and the diagnosis is eased by the improved diagnostic capacity of the instruments used. The aim of the present study is the evaluation of occupational exposure to ionizing radiation as a possible significant risk factor in the determinism of this pathology. Method: A cross-sectional observational study in “A category” X-ray exposed workers (doctors, nurses, technicians) of the University Hospital of Palermo, compared with a sample of the general population, was carried out from June 2016 to June 2017. We evaluated data obtained from the Personal Health Records, includi…
Collisionless shock heating of heavy ions in SN 1987A
2019
Astrophysical shocks at all scales, from those in the heliosphere up to the cosmological shock waves, are typically "collisionless", because the thickness of their jump region is much shorter than the collisional mean free path. Across these jumps, electrons, protons, and ions are expected to be heated at different temperatures. Supernova remnants (SNRs) are ideal targets to study collisionless processes because of their bright post-shock emission and fast shocks. Although optical observations of Balmer-dominated shocks in young SNRs showed that the post-shock proton temperature is higher than the electron temperature, the actual dependence of the post-shock temperature on the particle mass…
XMM-Newton large programme on SN1006 - II. Thermal emission
2016
Based on the XMM-Newton large program on SN1006 and our newly developed spatially resolved spectroscopy tools (Paper~I), we study the thermal emission from ISM and ejecta of SN1006 by analyzing the spectra extracted from 583 tessellated regions dominated by thermal emission. With some key improvements in spectral analysis as compared to Paper~I, we obtain much better spectral fitting results with less residuals. The spatial distributions of the thermal and ionization states of the ISM and ejecta show different features, which are consistent with a scenario that the ISM (ejecta) is heated and ionized by the forward (reverse) shock propagating outward (inward). Different elements have differe…
AE Aurigae: First detection of non-thermal X-ray emission from a bow shock produced by a runaway star
2012
Runaway stars produce shocks when passing through interstellar medium at supersonic velocities. Bow shocks have been detected in the mid-infrared for several high-mass runaway stars and in radio waves for one star. Theoretical models predict the production of high-energy photons by non-thermal radiative processes in a number sufficiently large to be detected in X-rays. To date, no stellar bow shock has been detected at such energies. We present the first detection of X-ray emission from a bow shock produced by a runaway star. The star is AE Aur, which was likely expelled from its birthplace due to the encounter of two massive binary systems and now is passing through the dense nebula IC 405…