Search results for "X-Rays"
showing 10 items of 445 documents
HINODE /EIS SPECTROSCOPIC VALIDATION OF VERY HOT PLASMA IMAGED WITH THE SOLAR DYNAMICS OBSERVATORY IN NON-FLARING ACTIVE REGION CORES
2012
We use coronal imaging observations with SDO/AIA, and Hinode/EIS spectral data, to explore the potential of narrow band EUV imaging data for diagnosing the presence of hot (T >~5MK) coronal plasma in active regions. We analyze observations of two active regions (AR 11281, AR 11289) with simultaneous AIA imaging, and EIS spectral data, including the CaXVII line (at 192.8A) which is one of the few lines in the EIS spectral bands sensitive to hot coronal plasma even outside flares. After careful coalignment of the imaging and spectral data, we compare the morphology in a 3 color image combining the 171, 335, and 94A AIA spectral bands, with the image obtained for CaXVII emission from the an…
The density of coronal plasma in active stellar coronae
2004
We have analyzed high-resolution X-ray spectra of a sample of 22 active stars observed with the High Energy Transmission Grating Spectrometer on {\em Chandra} in order to investigate their coronal plasma density. Densities where investigated using the lines of the He-like ions O VII, Mg XI, and Si XIII. While Si XIII lines in all stars of the sample are compatible with the low-density limit, Mg XI lines betray the presence of high plasma densities ($> 10^{12}$ cm$^{-3}$) for most of the sources with higher X-ray luminosity ($> 10^{30}$ erg/s); stars with higher $L_X$ and $L_X/L_{bol}$ tend to have higher densities at high temperatures. Ratios of O VII lines yield much lower densities …
Closure relations during the plateau emission of Swift GRBs and the fundamental plane
2021
The Neil Gehrels Swift observatory observe Gamma-Ray bursts (GRBs) plateaus in X-rays. We test the reliability of the closure relations through the fireball model when dealing with the GRB plateau emission. We analyze 455 X-ray lightcurves (LCs) collected by \emph{Swift} from 2005 (January) until 2019 (August) for which the redshift is both known and unknown using the phenomenological Willingale 2007 model. Using these fits, we analyze the emission mechanisms and astrophysical environments of these GRBs through the closure relations within the time interval of the plateau emission. Finally, we test the 3D fundamental plane relation (Dainotti relation) which connects the prompt peak luminosi…
IGR J17451-3022: a dipping and eclipsing low mass X-ray binary
2016
In this paper, we report on the available X-ray data collected by INTEGRAL, Swift, and XMM-Newton during the first outburst of the INTEGRAL transient IGR J17451-3022, discovered in 2014 August. The monitoring observations provided by the JEM-X instruments on-board INTEGRAL and the Swift/XRT showed that the event lasted for about 9 months and that the emission of the source remained soft for the entire period. The source emission is dominated by a thermal component (kT~1.2 keV), most likely produced by an accretion disk. The XMM-Newton observation carried out during the outburst revealed the presence of multiple absorption features in the soft X-ray emission that could be associated to the p…
A relativistic iron emission line from the neutron star low-mass X-ray binary GX 3+1
2012
We present the results of a spectroscopic study of the Fe K{\alpha} emission of the persistent neutron-star atoll low-mass X-ray binary and type I X-ray burster GX 3+1 with the EPIC-PN on board XMM-Newton. The source shows a flux modulation over several years and we observed it during its fainter phase, which corresponds to an X-ray luminosity of Lx~10^37 ergs/s. When fitted with a two-component model, the X-ray spectrum shows broad residuals at \sim6-7 keV that can be ascribed to an iron K{\alpha} fluorescence line. In addition, lower energy features are observed at \sim3.3 keV, \sim3.9 keV and might originate from Ar XVIII and Ca XIX. The broad iron line feature is well fitted with a rela…
LeMMINGs - IV. The X-ray properties of a statistically complete sample of the nuclei in active and inactive galaxies from the Palomar sample
2022
All 280 of the statistically complete Palomar sample of nearby ( 20° have been observed at 1.5 GHz as part of the LeMMINGs e-MERLIN legacy survey. Here, we present Chandra X-ray observations of the nuclei of 213 of these galaxies, including a statistically complete sub-set of 113 galaxies in the declination range 40° <δ < 65°. We observed galaxies of all optical spectral types, including ‘active’ galaxies [e.g. low-ionization nuclear emission line regions (LINERs) and Seyferts] and ‘inactive’ galaxies like HII galaxies and absorption line galaxies (ALG). The X-ray flux limit of our survey is 1.65 × 10−14 erg s−1 cm−2 (0.3−10 keV). We detect X-ray emission coincident within 2 arcsec of the n…
X-ray Flares of EV Lac: Statistics, Spectra, Diagnostics
2010
We study the spectral and temporal behavior of X-ray flares from the active M-dwarf EV Lac in 200 ks of exposure with the Chandra/HETGS. We derive flare parameters by fitting an empirical function which characterizes the amplitude, shape, and scale. The flares range from very short (<1 ks) to long (10 ks) duration events with a range of shapes and amplitudes for all durations. We extract spectra for composite flares to study their mean evolution and to compare flares of different lengths. Evolution of spectral features in the density-temperature plane shows probable sustained heating. The short flares are significantly hotter than the longer flares. We determined an upper limit to the Fe…
A ionized reflecting skin above the accretion disk of GX 349+2
2009
The broad emission features in the Fe-Kalpha region of X-ray binary spectra represent an invaluable probe to constrain the geometry and the physics of these systems. Several Low Mass X-ray binary systems (LMXBs) containing a neutron star (NS) show broad emission features between 6 and 7 keV and most of them are nowi nterpreted as reflection features from the inner part of an accretion disk in analogy to those observed in the spectra of X-ray binary systems containing a Black Hole candidate. The NS LMXB GX 349+2 was observed by the XMM-Newton satellite which allows, thanks to its high effective area and good spectral resolution between 6 and 7 keV, a detailed spectroscopic study of the Fe-Ka…
The Chandra COSMOS Survey, I: Overview and Point Source Catalog
2009
The Chandra COSMOS Survey (C-COSMOS) is a large, 1.8 Ms, Chandra} program that has imaged the central 0.5 sq.deg of the COSMOS field (centered at 10h, +02deg) with an effective exposure of ~160ksec, and an outer 0.4sq.deg. area with an effective exposure of ~80ksec. The limiting source detection depths are 1.9e-16 erg cm(-2) s(-1) in the Soft (0.5-2 keV) band, 7.3e(-16) erg cm^-2 s^-1 in the Hard (2-10 keV) band, and 5.7e(-16) erg cm(-2) s(-1) in the Full (0.5-10 keV) band. Here we describe the strategy, design and execution of the C-COSMOS survey, and present the catalog of 1761 point sources detected at a probability of being spurious of <2e(-5) (1655 in the Full, 1340 in the Soft, and…
XMM-Newton evidence of shocked ISM in SN 1006: indications of hadronic acceleration
2012
Shock fronts in young supernova remnants are the best candidates for being sites of cosmic ray acceleration up to a few PeV, though conclusive experimental evidence is still lacking. Hadron acceleration is expected to increase the shock compression ratio, providing higher postshock densities, but X-ray emission from shocked ambient medium has not firmly been detected yet in remnants where particle acceleration is at work. We exploited the deep observations of the XMM-Newton Large Program on SN 1006 to verify this prediction. We performed spatially resolved spectral analysis of a set of regions covering the southeastern rim of SN 1006. We studied the spatial distribution of the thermodynamic…