An XMM and Chandra view of massive clusters of galaxies to z=1

The X-ray properties of a sample of high redshift (z>0.6), massive clusters observed with XMM-Newton and Chandra are described, including two exceptional systems. One, at z=0.89, has an X-ray temperature of T=11.5 (+1.1, -0.9) keV (the highest temperature of any cluster known at z>0.6), an estimated mass of (1.4+/-0.2)x10^15 solar masses and appears relaxed. The other, at z=0.83, has at least three sub-clumps, probably in the process of merging, and may also show signs of faint filamentary structure at large radii,observed in X-rays. In general there is a mix of X-ray morphologies, from those clusters which appear relaxed and containing little substructure to some highly non-virialized and probably merging systems. The X-ray gas metallicities and gas mass fractions of the relaxed systems are similar to those of low redshift clusters of the same temperature, suggesting that the gas was in place, and containing its metals, by z=0.8. The evolution of the mass-temperature relation may be consistent with no evolution or with the ``late formation'' assumption. The effect of point source contamination in the ROSAT survey from which these clusters were selected is estimated, and the implications for the ROSAT X-ray luminosity function discussed.Comment: 9 pages, in Carnegie Observatories Astrophysics Series, Vol. 3: Clusters of Galaxies: Probes of Cosmological Structure and Galaxy Evolution, ed. J. S. Mulchaey, A. Dressler, and A. Oemler. See http://www.ociw.edu/ociw/symposia/series/symposium3/proceedings.html for a full-resolution versio

The X-ray spectrum of the Seyfert I galaxy Markarian 766: Dusty warm absorber or relativistic emission lines?

Competing models for broad spectral features in the soft X-ray spectrum of the Seyfert I galaxy Mrk 766 are tested against data from a 130 ks XMM-Newton observation. A model including relativistically broadened Lyalpha emission lines of O VIII N VII and C VI is a better fit to 0.3-2 keV XMM RGS data than a dusty warm absorber. Moreover, the measured depth of neutral iron absorption lines in the spectrum is inconsistent with the magnitude of the iron edge required to produce the continuum break at 17-18 Angstrom in the dusty warm absorber model. The relativistic emission line model can reproduce the broadband (0.1-12 keV) XMM EPIC data with the addition of a fourth line to represent emission from ionized iron at 6.7 keV and an excess due to reflection at energies above the iron line. The pro le of the 6.7 keV iron line is consistent with that measured for the low-energy lines. There is evidence in the RGS data, at the 3sigma level, of spectral features that vary with source flux. The covering fraction of warm absorber gas is estimated to be 12%. Iron in the warm absorber is found to be overabundant with respect to CNO, compared to solar values

Past, Present, and Future X-Ray and Gamma-Ray Missions

X- and -ray astronomy began in the early sixties of the last century with balloons flights, sounding rocket experiment and satellites. Long before space satellite detected X- and -rays emitted by cosmic sources, scientists had known that the Universe should be producing these photons. In this chapter we provided an overview of past and present missions that has made the X- and -ray astronomy an integral part of astronomical research, and prospects of future developments

Simultaneous IR and optical light curves of 2A0311−227

Original article can be found at: http://www.nature.com/nature/index.html Copyright Nature Publishing Group. DOI: 10.1038/301223a0 [Full text of this article is not available in the UHRA]The complex wavelength dependence shown by the light curves of the AM Herculis type binaries such as 2A0311−227 (EFERI) and AM Her itself has led to suggestions that accretion occurs onto both magnetic poles of the white dwarf. The field strengths of the two poles being sufficiently different that one pole dominates at optical wavelengths, while the other produces most of the emission in the IR. Other authors have argued for a single pole model explaining the wavelength dependence of the light curves in terms of the rapidly changing cyclotron opacity with wavelength. An observational method of distinguishing between these two models is provided by the rapid flickering, which is a characteristic property of the light curves at both optical and IR wavelengths. We report here that the optical and IR flickering of 2A0311−227 are highly correlated indicating that in this object the dominant source of cyclotron radiation at both wavelengths is the same accretion column.Peer reviewe

IR photometry and polarimetry of 2A0311−227

Original article can be found at: http://www.nature.com/nature/index.html Copyright Nature Publishing Group. DOI: 10.1038/285306a0 [Full text of this article is not available in the UHRA]The X-ray source 2A0311 − 227 has recently been identified with a star whose spectrum and polarization properties show it to be an AM Herculis type binary. These binaries are thought to consist of a synchronously rotating magnetic white dwarf, with a surface field of 108G, accreting matter from a cooler companion star. The highly circularly polarized radiation emitted by these systems is thought to be due to cyclotron radiation originating in an accretion column at one or both poles of the white dwarf. We describe here IR light curves of 2A0311 − 227 at 1.25 and 2.2µm, together with circular polarimetry at 1.25µm. The light curves show a deep narrow minimum which does not have an optical counterpart, and the 1.25µm polarimetry shows circular polarization which is much lower than that in the optical.Peer reviewe