X-ray Telescopes (x-ray + telescope)

Distribution by Scientific Domains

Selected Abstracts

Probing the nature of IGR J16493,4348: spectral and temporal analysis of the 1,100 keV emission

A. B. Hill
ABSTRACT IGR J16493,4348 was one of the first new sources to be detected by the INTErnational Gamma-Ray Astrophysics Laboratory (INTEGRAL) ,-ray telescope in the 18,100 keV energy band. Based on spatial coincidence, the source was originally associated with the free radio pulsar PSR J1649,4349. Presented here are the results of 2.8 Ms of observations made by the INTEGRAL mission and a 5.6-ks observation with the Swift/X-ray Telescope (XRT). Spectral analysis indicates that the source is best modelled by an absorbed power law with a high energy cut-off at Ecut, 15 keV and a hydrogen absorbing column of NH= 5.4+1.3,1 1022 cm,2. Analysis of the light curves indicates that the source is a weak, persistent ,-ray emitter showing indications of variability in the 2,9 and 22,100 keV bands. The average source flux is ,1.1 10,10 erg cm,2 s,1 in the 1,100 keV energy band. No coherent timing signal is identified at any time-scale in the INTEGRAL or Swift data. The refined source location and positional uncertainty of IGR J16493,4348 places PSR J1649,4349 outside the 90 per cent error circle. We conclude that IGR J16493,4348 is not associated with PSR J1649,4349. Combining the INTEGRAL observations with Swift/XRT data and information gathered by RXTE and Chandra, we suggest that IGR J16493,4348 is an X-ray binary, and that the source characteristics favour a high-mass X-ray binary although a low-mass X-ray binary nature cannot be ruled out. [source]

Review of Hinode results

Y. Suematsu
Abstract Hinode is an observatory-style satellite, carrying three advanced instruments being designed and built to work together to explore the physical coupling between the photosphere and the upper layers for understanding the mechanism of dynam- ics and heating. The three instruments aboard are the Solar Optical Telescope (SOT), which can provide high-precision photometric and polarimetric data of the lower atmosphere in the visible light (388,668 nm) with a spatial resolution of 0.2,0.3 arcseconds, the X-Ray Telescope (XRT) which takes a wide field of full sun coverage X-ray images being capable of diagnosing the physical condition of coronal plasmas, and the EUV Imaging Spectrometer (EIS) which observes the upper transition region and coronal emission lines in the wavelength ranges of 17,21 nm and 25,29 nm. Since first-light observations in the end of October 2006, Hinode has been continuously providing unprecedented high-quality solar data. We will present some new findings of the sun with Hinode, focusing on those from SOT ( 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Productivity and impact of astronomical facilities: A recent sample

V. Trimble
Abstract The papers published in 11 key astronomical journals in 2008, and a year of citations to those from the first half of the year, have been associated with the telescopes, satellites, and so forth where the data were gathered using a form of fractional counting. Some numbers are also given by journal, by subfield, and by wavelength band. The largest numbers of papers, and generally also quite highly cited ones, in their respective wavelength bands come from the Very Large Array, the Hubble Space Telescope, the Sloan Digital Sky Survey, the Spitzer Space Telescope, and the Chandra X-ray Telescope. Optical astronomy is still the largest sector; and papers about cosmology and exoplanets are cited more often than papers about binary stars and planetary nebulae. The authors conclude that it is of equal importance to recognize (a) that a very large number of papers also come from less famous facilities, (b) that a very large fraction of papers (and their authors) are concerned with the less highly-cited topics, (c) that many facilities are quite slow in achieving their eventual level of influence, and (d) that one really needs at least three years of citation data, not just one or two, to provide a fair picture of what is going on ( 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Hard X-ray emission of the Earth's atmosphere: Monte Carlo simulations

S. Sazonov
ABSTRACT We perform Monte Carlo simulations of cosmic ray-induced hard X-ray radiation from the Earth's atmosphere. We find that the shape of the spectrum emergent from the atmosphere in the energy range 25,300 keV is mainly determined by Compton scatterings and photoabsorption, and is almost insensitive to the incident cosmic ray spectrum. We provide a fitting formula for the hard X-ray surface brightness of the atmosphere as would be measured by a satellite-borne instrument, as a function of energy, solar modulation level, geomagnetic cut-off rigidity and zenith angle. A recent measurement by the INTEGRAL observatory of the atmospheric hard X-ray flux during the occultation of the cosmic X-ray background by the Earth agrees with our prediction within 10 per cent. This suggests that Earth observations could be used for in-orbit calibration of future hard X-ray telescopes. We also demonstrate that the hard X-ray spectra generated by cosmic rays in the crusts of the Moon, Mars and Mercury should be significantly different from that emitted by the Earth's atmosphere. [source]

The ROSAT Brightest Cluster Sample , IV.

The extended sample
We present a low-flux extension of the X-ray-selected ROSAT Brightest Cluster Sample (BCS) published in Paper I of this series. Like the original BCS and employing an identical selection procedure, the BCS extension is compiled from ROSAT All-Sky Survey (RASS) data in the northern hemisphere (,,0) and at high Galactic latitudes (|b|,20). It comprises 99 X-ray-selected clusters of galaxies with measured redshifts z,0.3 (as well as eight more at z>0.3) and total fluxes between 2.810,12 and 4.410,12 erg cm,2 s,1 in the 0.1,2.4 keV band (the latter value being the flux limit of the original BCS). The extension can be combined with the main sample published in 1998 to form the homogeneously selected extended BCS (eBCS), the largest and statistically best understood cluster sample to emerge from the RASS to date. The nominal completeness of the combined sample (defined with respect to a power-law fit to the bright end of the BCS log N,log S distribution) is relatively low at 75 per cent (compared with 90 per cent for the high-flux sample of Paper I). However, just as for the original BCS, this incompleteness can be accurately quantified, and thus statistically corrected for, as a function of X-ray luminosity and redshift. In addition to its importance for improved statistical studies of the properties of clusters in the local Universe, the low-flux extension of the BCS is also intended to serve as a finding list for X-ray-bright clusters in the northern hemisphere which we hope will prove useful in the preparation of cluster observations with the next generation of X-ray telescopes such as Chandra and XMM-Newton. An electronic version of the eBCS can be obtained from the following URL: http://www.ifa.hawaii.edu/~ebeling/clusters/BCS.html. [source]

HI , the window to the early universe in X-rays

J. Kerp
Abstract A detailed understanding of the soft X-ray background (SXRB) is of high importance for the next generation of X-ray telescopes, which will focus on early universe objects. Because of their high redshift the characteristic X-ray emission of the early universe objects will be observable in the soft X-ray energy domain below E = 1 keV. In this energy regime the photoelectric absorption of the galactic interstellar medium attenuates the X-ray emission most strongly. The confusion with the spatially highly variable galactic soft X-ray emission might be an additional severe problem to disentangle the emission of the early universe object and the SXRB. We present the cross correlation of the Leiden/Dwingeloo HI 21-cm line survey with the ROSAT all-sky survey. The analyses disclose the existence of a single temperature plasma within the Milky Way halo. The strength of the photoelectric absorption is quantitatively traced by the distribution of the HI emission across the whole sky. Both findings in combination open the window to the highly redshift early universe objects. [source]