680 research outputs found
The 2XMMi/SDSS Galaxy Cluster Survey. III. Clusters associated with spectroscopically targeted luminous red galaxies in SDSS-DR10
We present a sample of 383 X-ray selected galaxy groups and clusters with
spectroscopic redshift measurements (up to z ~ 0.79) from the 2XMMi/SDSS Galaxy
Cluster Survey. The X-ray cluster candidates were selected as serendipitously
detected sources from the 2XMMi-DR3 catalogue that were located in the
footprint of the Sloan Digital Sky Survey (SDSS-DR7). The cluster galaxies with
available spectroscopic redshifts were selected from the SDSS-DR10. We
developed an algorithm for identifying the cluster candidates that are
associated with spectroscopically targeted luminous red galaxies and for
constraining the cluster spectroscopic redshift. A cross-correlation of the
constructed cluster sample with published optically selected cluster catalogues
yielded 264 systems with available redshifts. The present redshift measurements
are consistent with the published values. The current cluster sample extends
the optically confirmed cluster sample from our cluster survey by 67 objects.
Moreover, it provides spectroscopic confirmation for 78 clusters among our
published cluster sample, which previously had only photometric redshifts. Of
the new cluster sample that comprises 67 systems, 55 objects are newly X-ray
discovered clusters and 52 systems are sources newly discovered as galaxy
clusters in optical and X-ray wavelengths. Based on the measured redshifts and
the fluxes given in the 2XMMi-DR3 catalogue, we estimated the X-ray
luminosities and masses of the cluster sample.Comment: A&A in press, 12 pages, 15 figures, 1 table,
http://www.aanda.org/index.php?option=com_article&access=doi&doi=10.1051/0004-6361/20132297
The 2XMMi/SDSS Galaxy Cluster Survey. II. The optically confirmed cluster sample and the L_X-T relation
We compile a sample of X-ray-selected galaxy groups and clusters from the
XMM-Newton serendipitous source catalogue (2XMMi-DR3) with optical confirmation
and redshift measurement from the Sloan Digital Sky Survey (SDSS). The X-ray
cluster candidates were selected from the 2XMMi-DR3 catalogue in the footprint
of the SDSS-DR7. We developed a finding algorithm to search for overdensities
of galaxies at the positions of the X-ray cluster candidates in the photometric
redshift space and to measure the redshifts of the clusters from the SDSS data.
The detection algorithm provides the photometric redshift of 530 galaxy
clusters. Of these, 310 clusters have a spectroscopic redshift for at least one
member galaxy. About 75 percent of the optically confirmed cluster sample are
newly discovered X-ray clusters. Moreover, 301 systems are known as optically
selected clusters in the literature while the remainder are new discoveries in
X-ray and optical bands. The optically confirmed cluster sample spans a wide
redshift range 0.03-0.70 (median z=0.32). In this paper, we present the
catalogue of X-ray-selected galaxy groups and clusters from the 2XMMi/SDSS
galaxy cluster survey. The catalogue has two subsamples: (i) a cluster sample
comprising 345 objects with their X-ray spectroscopic temperature and flux from
the spectral fitting, and (ii) a cluster sample consisting of 185 systems with
their X-ray flux from the 2XMMi-DR3 catalogue, because their X-ray data are
insufficient for spectral fitting. The updated L_X-T relation of the current
sample with X-ray spectroscopic parameters is presented. We see no evidence for
evolution in the slope and intrinsic scatter of the L_X-T relation with
redshift when excluding the low-luminosity groups.Comment: A&A in press, 18 pages, 25 figures, 3 tables (revised version after
language editing
XMM-Newton and optical observations of the eclipsing polar CSS081231:071126+440405
Aims: We aim to study the temporal and spectral behaviour of the eclipsing
polar CSS081231:071126+440405 from the infrared to the X-ray regime.
Methods: We obtained phase-resolved XMM-Newton X-ray observations on two
occasions in 2012 and 2013 in different states of accretion. In 2013 the
XMM-Newton X-ray and UV data were complemented by optical photometric and
spectroscopic observations.
Results: CSS081231 displays two-pole accretion in the high state. The
magnetic fields of the two poles are 36 and 69 MG, indicating a non-dipolar
field geometry. The X-ray spectrum of the main accreting pole with the lower
field comprises a hot thermal component from the cooling accretion plasma,
of a few tens of keV, and a much less luminous blackbody-like
component from the accretion area with 50-100\,eV. The
high-field pole which was located opposite to the mass-donating star accretes
at a low rate and has a plasma temperature of about 4\,keV. At both occasions
the X-ray eclipse midpoint precedes the optical eclipse midpoint by 3.2
seconds. The center of the X-ray bright phase shows accretion-rate dependent
longitudinal motion of ~20 degrees.
Conclusions: CSS081231 is a bright polar that escaped detection in the RASS
survey because it was in a low accretion state. Even in the high state it lacks
the prominent soft component previously thought ubiquitous in polars. Such an
excess may still be present in the unobserved extreme ultraviolet. All polars
discovered in the XMM-Newton era lack the prominent soft component. The
intrinsic spectral energy distribution of polars still awaits characterisation
by future X-ray surveys such as eROSITA. The trajectory taken by material to
reach the second pole is still uncertain.Comment: 12 pages, 14 figure
A long-term optical and X-ray ephemeris of the polar EK Ursae Majoris
We searched for long-term period changes in the polar EK UMa using new
optical data and archival X-ray/EUV data. An optical ephemeris was derived from
data taken remotely with the MONET/N telescope and compared with the X-ray
ephemeris based on Einstein, Rosat, and EUVE data. A three-parameter fit to the
combined data sets yields the epoch, the period, and the phase offset between
the optical minima and the X-ray absorption dips. An added quadratic term is
insignificant and sets a limit to the period change. The derived linear
ephemeris is valid over 30 years and the common optical and X-ray period is
P=0.0795440225(24) days. There is no evidence of long-term O-C variations or a
period change over the past 17 years Delta P = -0.14+-0.50 ms. We suggest that
the observed period is the orbital period and that the system is tightly
synchronized. The limit on Delta P and the phase constancy of the bright part
of the light curve indicate that O-C variations of the type seen in the polars
DP Leo and HU Aqr or the pre-CV NN Ser do not seem to occur in EK UMa. The
X-ray dips lag the optical minima by 9.5+-0.7 deg in azimuth, providing some
insight into the accretion geometry.Comment: 4 pages, 2 Postscript figures, accepted for publication in Astronomy
& Astrophysic
The serendipituous discovery of a short-period eclipsing polar in 2XMMp
We report the serendipituous discovery of the new eclipsing polar 2XMMp
J131223.4+173659. Its striking X-ray light curve attracted immediate interest
when we were visually inspecting the source products of the 2XMMp catalogue.
This light curve revealed its likely nature as a magnetic cataclysmic variable
of AM Herculis (or polar) type with an orbital period of ~92 min, which was
confirmed by follow-up optical spectroscopy and photometry. 2XMMp
J131223.4+173659 probably has a one-pole accretion geometry. It joins the group
of now nine objects that show no evidence of a soft component in their X-ray
spectra despite being in a high accretion state, thus escaping ROSAT/EUVE
detection. We discuss the likely accretion scenario, the system parameters, and
the spectral energy distribution.Comment: Accepted for publication in A&
Probing the accretion processes in soft X-ray selected polars
High-energy data of accreting white dwarfs give access to the regime of the
primary accretion-induced energy release and the different proposed accretion
scenarios. We perform XMM-Newton observations of polars selected due to their
ROSAT hardness ratios close to -1.0 and model the emission processes in
accretion column and accretion region. Our models consider the
multi-temperature structure of the emission regions and are mainly determined
by mass-flow density, magnetic field strength, and white-dwarf mass. To
describe the full spectral energy distribution from infrared to X-rays in a
physically consistent way, we include the stellar contributions and establish
composite models, which will also be of relevance for future X-ray missions. We
confirm the X-ray soft nature of three polars.Comment: Accepted for publication in Acta Polytechnica, Proceedings of "The
Golden Age of Cataclysmic Variables and Related Objects II
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