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ROSAT Observations (rosat + observation)

Distribution by Scientific Domains
Physics and Astronomy100%

Selected Abstracts

The warm absorber of the type 1 Seyfert galaxy H1419+480

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 3 2003
X. Barcons
ABSTRACT The bright type 1 Seyfert galaxy H1419+480 (z, 0.072), whose X-ray colours from earlier HEAO-1 and ROSAT missions suggested a complex X-ray spectrum, has been observed with XMM,Newton. The EPIC spectrum above 2 keV is well fitted by a power law with photon index ,= 1.84 ± 0.01 and an Fe K, line of equivalent width ,250 eV. At softer energies, a decrement with respect to this model extending from 0.5 to 1 keV is clearly detected. After trying a number of models, we find that the best fit corresponds to O vii absorption at the emission redshift, plus a 2, detection of O viii absorption. A photoionized gas model fit yields log ,, 1.15,1.30 (, in erg cm s,1) with NH, 5 × 1021 cm,2 for solar abundances. We find that the ionized absorber was weaker or absent in an earlier ROSAT observation. An International Ultraviolet Explorer spectrum of this source obtained two decades before shows a variable (within a year) C iv absorber outflowing with a velocity ,1800 km s,1. We show that both X-ray and ultraviolet absorptions are consistent with arising in the same gas, with varying ionization. [source]

A systematic study of low-mass X-ray binaries in the M31 globular cluster system

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2010
Mark B. Peacock
ABSTRACT We investigate low-mass X-ray binaries (LMXBs) in the M31 globular cluster (GC) system using data from the 2XMMi catalogue. These X-ray data are based on all publicly available XMM,Newton observations of the galaxy. This new survey provides the most complete and homogeneous X-ray survey of M31's GCs to date, covering >80 per cent of the confirmed old clusters in the galaxy. We associate 41 X-ray sources with confirmed old clusters in the recent M31 cluster catalogue of Peacock et al. Comparing these data with previous surveys of M31, it is found that three of these clusters are newly identified, including a bright transient source in the cluster B128. Four additional clusters, that are not detected in these 2XMMi data, have previously been associated with X-ray sources from Chandra or ROSAT observations. Including these clusters, we identify 45 clusters in M31 which are associated with X-ray emission. By considering the latest optical GC catalogues, we identify that three of the previously proposed X-ray clusters are likely to be background galaxies and two have stellar profiles. We consider the properties of LMXB hosting clusters and confirm significant trends between the presence of an LMXB and the metallicity, luminosity and stellar collision rate of a cluster. We consider the relationship between the luminosity and stellar collision rate of a cluster and note that LMXB hosting clusters have higher than average stellar collision rates for their mass. Our findings strongly suggest that the stellar collision rate is the dominant parameter related to the presence of LMXBs. This is consistent with the formation of LMXBs in GCs through dynamical interactions. [source]

The environments of FRII radio sources

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2000
M. J. Hardcastle
Using ROSAT observations, we estimate gas pressures in the X-ray-emitting medium surrounding 63 FRII radio galaxies and quasars. We compare these pressures with the internal pressures of the radio-emitting plasma estimated by assuming minimum energy or equipartition. In the majority of cases (including 12/13 sources with modelled, spatially resolved X-ray emission) radio sources appear to be underpressured with respect to the external medium, suggesting that simple minimum-energy arguments underestimate the internal energy density of the sources. We discuss possible departures from the minimum-energy condition and the consequences of our result for models of the dynamics of radio galaxies, in particular self-similar models. [source]

X-ray emission from optical novae in M 31,

ASTRONOMISCHE NACHRICHTEN, Issue 2 2010
W. Pietsch
Abstract The first supersoft source (SSS) identification with an optical nova in M 31 was based on ROSAT observations. Twenty additional X-ray counterparts (mostly identified as SSS by their hardness ratios) were detected using archival ROSAT, XMM-Newton and Chandra observations obtained before July 2002. Based on these results optical novae seem to constitute the major class of SSS in M 31. An analysis of archival Chandra HRC-I and ACIS-I observations obtained from July 2004 to February 2005 demonstrated that M 31 nova SSS states lasted from months to about 10 years. Several novae showed short X-ray outbursts starting within 50 d after the optical outburst and lasting only two to three months. The fraction of novae detected in soft X-rays within a year after the optical outburst was more than 30%. Ongoing optical nova monitoring programs, optical spectral follow-up and an up-to-date nova catalogue are essential for the X-ray work. Re-analysis of archival nova data to improve positions and find additional nova candidates are urgently needed for secure recurrent nova identifications. Dedicated XMM-Newton/Chandra monitoring programs for X-ray emission from optical novae covering the centre area of M 31 continue to provide interesting new results (e.g. coherent 1105 s pulsations in the SSS counterpart of nova M31N 2007-12b). The SSS light curves of novae allow us , together with optical information , to estimate the mass of the white dwarf, of the ejecta and the burned mass in the outburst. Observations of the central area of M 31 allow us , in contrast to observations in the Galaxy , to monitor many novae simultaneously and proved to be prone to find many interesting SSS and nova types (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]