X-ray Observatory (x-ray + observatory)

Distribution by Scientific Domains

Kinds of X-ray Observatory

  • chandra x-ray observatory

  • Selected Abstracts

    A Chandra observation of the disturbed cluster core of Abell 2204

    J. S. Sanders
    ABSTRACT We present results from an observation of the luminous cluster of galaxies Abell 2204 using the Chandra X-ray Observatory. We show the core of the cluster has a complex morphological structure, made up of a high-density core (ne, 0.2 cm,3) with flat surface brightness, a surrounding central plateau, a tail-like feature, wrapping around to the east, and an unusual radio source. A temperature map and deprojected profile shows that the temperature rises steeply outside these regions, until around ,100 kpc where it drops, then rises again. Abundance maps and profiles show that there is a corresponding increase in abundance at the same radius as where the temperature drops. In addition, there are two cold fronts at radii of ,28 and 54.5 kpc. The disturbed morphology indicates that the cluster core may have undergone a merger. However, despite this disruption, the mean radiative cooling time in the centre is short (,230 Myr) and the morphology is regular on large scales. [source]

    X-ray emission from GPS and CSS sources

    A. Siemiginowska
    Abstract Many X-ray observations of GigaHertz Peaked Spectrum and Compact Steep Spectrum sources have been made with Chandra X-ray Observatory and XMM-Newton Observatory over the last few years. The X-ray spectra contribute the important information to the total energy distribution of the compact radio sources. In addition the spatial resolution of Chandra allows for studies of the X-ray morphology of these sources on arcsec scales and provide a direct view of their environments. This paper gives a review of the current status of the X-ray observations and their contribution to our understanding of the nature of these compact radio sources. It also describes primary physical processes that lead to the observed X-ray emission and summarize X-ray emission properties expected from interactions between an expanding radio source and the intergalactic environment ( 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

    Chandra ACIS Imaging Spectroscopy of Sgr A East

    Y. Maeda
    Abstract We report on the X-ray emission from the shell-like, non-thermal radio source Sgr A East located in the inner few parsecs of the Galaxy based on observations made with the ACIS detector on board the Chandra X-ray Observatory. The X-ray emission from Sgr A East is concentrated within the central ,2 pc of the larger radio shell. The spectrum shows strong K, lines from highly ionized ions of S, Ar, Ca, and Fe. A simple isothermal plasma model gives electron temperature ,2 keV, absorption column ,1 1023 H cm,2, luminosity ,8 1034 ergs s,1 in the 2,10 keV band, and gas mass ,2, M, with a filling factor ,. The plasma appears to be rich in heavy elements, over-abundant by roughly a factor of four with respect to solar abundances. Accompanied with filamentary or blob-like structures, the plasma shows a spatial gradient of elemental abundance: the spatial distribution of iron is more compact than that of the lighter elements. These Chandra results strongly support the long-standing hypothesis that Sgr A East is a supernova remnant (SNR). Since Sgr A East surrounds Sgr A* in projection, it is possible that the dust ridge compressed by the forward shock of Sgr A East hit Sgr A* in the past, and the passage of the ridge may have supplied material to accrete onto the black hole in the past, and may have removed material from the black hole vicinity, leading to its present quiescent state. [source]

    Limits on the Short Term Variability of Sagittarius A* in the Near-Infrared

    S. D. Hornstein
    Abstract The detection of X-ray flares by the Chandra X-ray Observatory and XMM-Newton has raised the possibility of enhanced emission over a broad range of wavelengths from Sagittarius A*, the suspected 2.6 106 M, black hole at the Galactic center, during a flaring event. We have, therefore, reconstructed 3,4 hr data sets from 2 ,m speckle and adaptive optics images (,core = 50,100 mas) obtained with the W. M. Keck 10 m telescopes between 1995 and 2002. The results for 25 of these observations were reported by Hornstein et al. (2002) and an additional 11 observations are presented here. In the 36 separate observations, no evidence of any significant excess emission associated with Sgr A* was detected. The lowest of our detection limits gives an observed limit for the quiescent state of Sgr A* of 0.09 0.005 mJy, or, equivalently, a dereddened value of 2.0 0.1 mJy. Under the assumption that there are random 3 hr flares producing both enhanced X-ray and near-infrared emission, our highest limit constrains the variable state of Sgr A* to ,0.8 mJy (observed) or 19 mJy (dereddened). These results suggest that the early model favored by Markoff et al. (2002), in which the flare is produced through local heating of relativistic particles surrounding Sgr A* (e.g., a sudden magnetic reconnection event), is unlikely because it predicts peak 2 ,m emission of ,300 mJy, well above our detection limit. [source]

    The hard X-ray spectrum of the Seyfert galaxy IRAS 18325,5926: reflection from an ionized disc and variable iron K emission

    K. Iwasawa
    ABSTRACT We report our analysis of the X-ray spectra of the Seyfert galaxy IRAS 18325,5926 (= Fairall 49) obtained from various X-ray observatories prior to XMM,Newton, including new results from two RXTE and one BeppoSAX observations. A relatively steep continuum slope (,, 2.2) in the 2,15 keV band is confirmed. The continuum spectrum observed with the BeppoSAX PDS shows a possible roll-over at energies above 30 keV, indicating a Comptonizing corona cooler than in other Seyfert nuclei. The X-ray spectrum above 2 keV is best explained with a model including reflection from a highly ionized disc with significant relativistic blurring. The iron K, emission feature is then mainly due to Fe xxv. The seven recent observations show that the iron K emission flux appears to follow the continuum between the observations separated by a few months to years, although some exceptions suggest that the linestrength may be determined in a more complex way. [source]

    The weak outnumbering the mighty: normal galaxies in deep Chandra surveys

    A. E. Hornschemeier
    Abstract Chandra is detecting a significant population of normal and starburst galaxies in extremely deep X-ray exposures. For example, approximately 15% of the sources arising in the 2 Ms Chandra Deep Field-North survey are fairly normal galaxies, where "normal" means "Milky Way-type" X-ray emission rather than simply exhibiting an "optically normal" spectrum. Many of these galaxies are being detected at large look-back times (z , 0.1,0.5), allowing the study of the evolution of X-ray binary populations over significant cosmological timescales. We are also detecting individual off-nuclear ultraluminous X-ray sources (e.g., X-ray binaries), providing the first direct constraints on the prevalence of lower-mass black holes at significantly earlier times. The X-ray emission from such "normal" galaxies may also be a useful star-formation rate indicator, based on radio/X-ray cross-identifications. We describe the contribution of normal galaxies to the populations which make up the X-ray background and present their directly measured X-ray number counts. We find that normal and starburst galaxies should dominate the 0.5,2 keV number counts at X-ray fluxes fainter than , 7 10,18 erg cm,2 s,1 (thus they will outnumber the "mighty" AGN). Finally, we look to the future, suggesting that it is important that the population of X-ray faint normal and starburst galaxies be well constrained in order to design the next generation of X-ray observatories. [source]

    Minor planets and major X-ray finds

    ASTRONOMY & GEOPHYSICS, Issue 6 2001
    Peter Bond
    Yohkoh and Ulysses keep a watching brief on the Sun and the solar wind, comets and minor planets appear in close-up, auroral symmetry is confirmed and, elsewhere, X-ray observatories continue to uncover the workings of the high-energy universe. Peter Bond reports. [source]

    Mixed fortunes for X-ray observatories

    ASTRONOMY & GEOPHYSICS, Issue 2 2000
    Article first published online: 24 DEC 200
    A new name for XMM, a boost for Hubble and the happy demise of a mirror ball satellite are among the space activities reported by Peter Bond. Peter Bond is the RAS PR Officeer (Space Science). [source]

    Establishing the nature of companion candidates to X-ray-emitting late B-type stars,

    S. Hubrig
    ABSTRACT The most favoured interpretation for the detection of X-ray emission from late B-type stars is that these stars have a yet undiscovered late-type companion (or an unbound nearby late-type star) that produces the X-rays. Several faint infrared objects at (sub)arcsecond separation from B-type stars have been uncovered in our earlier adaptive optics imaging observations, and some of them have been followed up with the high spatial resolution of the Chandra X-ray observatory, pinpointing the X-ray emitter. However, firm conclusions on their nature require a search for spectroscopic signatures of youth. Here we report on our recent ISAAC observations carried out in low-resolution spectroscopic mode. Equivalent widths have been used to obtain information on spectral types of the companions. All eight X-ray-emitting systems with late B-type primaries studied contain dwarf-like companions with spectral types later than A7. The only system in the sample where the companion turns out to be of early spectral type is not an X-ray source. These results are consistent with the assumption that the observed X-ray emission from late B-type stars is produced by an active pre-main-sequence companion star. [source]

    Chandra monitoring observations of the ultraluminous X-ray source NGC 5204 X-1

    T. P. Roberts
    ABSTRACT We report the results of a two-month campaign conducted with the Chandra X-ray observatory to monitor the ultraluminous X-ray source (ULX) NGC 5204 X-1. This was composed of a 50-ks observation, followed by ten 5-ks follow-ups spaced initially at ,3, then at ,10-d intervals. The ULX flux is seen to vary by factors ,5 on time-scales of a few days, but no strong variability is seen on time-scales shorter than an hour. There is no evidence for a periodic signal in the X-ray data. An examination of the X-ray colour variations over the period of the campaign shows the ULX emission consistently becomes spectrally harder as its flux increases. The X-ray spectrum from the 50-ks observation can be fitted by a number of disparate spectral models, all of which describe a smooth continuum with, unusually for a ULX, a broad emission feature evident at 0.96 keV. The spectral variations, both within the 50-ks observation and over the course of the whole campaign, can then be explained solely by variations in the continuum component. In the context of an optically thick corona model (as found in other recent results for ULXs) the spectral variations can be explained by the heating of the corona as the luminosity of the ULX increases, consistent with the behaviour of at least one Galactic black hole system in the strongly Comptonized very high state. We find no new evidence supporting the presence of an intermediate-mass black hole in this ULX. [source]