3,205 research outputs found
The XMM/2dF survey III: Comparison between optical and X-ray cluster detection methods
We directly compare X-ray and optical techniques of cluster detection by
combining SDSS photometric data with a wide-field ( deg)
XMM-{\em Newton} survey in the North Galactic Pole region. The optical cluster
detection procedure is based on merging two independent selection methods - a
smoothing+percolation technique, and a Matched Filter Algorithm. The X-ray
cluster detection is based on a wavelet-based algorithm, incorporated in the
SAS v.5.2 package. The final optical sample counts 9 candidate clusters with
richness of more than 20 galaxies, corresponding roughly to APM richness class.
Three, of our optically detected clusters are also detected in our X-ray
survey. The most probable cause of the small number of optical cluster
candidates detected in our X-ray survey is that they are relatively poor
clusters, fainter than the X-ray flux limit (for extended sources) of our
survey .Comment: 9 pages, 5 figures, MNRAS accepte
The Phoenix Deep Survey: X-ray properties of faint radio sources
In this paper we use a 50ks XMM-Newton pointing overlapping with the Phoenix
Deep Survey, a homogeneous radio survey reaching muJy sensitivities, to explore
the X-ray properties and the evolution of star-forming galaxies. UV, optical
and NIR photometry is available and is used to estimate photometric redshifts
and spectral types for radio sources brighter than R=21.5mag (total of 82).
Sources with R<21.5mag and spiral galaxy SEDs (34) are grouped into two
redshift bins with a median of z=0.240 and 0.455 respectively. Stacking
analysis for both the 0.5-2 and 2-8keV bands is performed on these subsamples.
A high confidence level signal (>3.5sigma) is detected in the 0.5-2keV band
corresponding to a mean flux of ~3e-16cgs for both subsamples. This flux
translates to mean luminosities of ~5e40 and 1.5e41cgs for the z=0.240 and
0.455 subsamples respectively. Only a marginally significant signal (2.6sigma)
is detected in the 2-8keV band for the z=0.455 subsample. We argue that the
stacked signal above is dominated by star-formation. The mean L_X/L_B ratio and
the mean L_X of the two subsamples are found to be higher than optically
selected spirals and similar to starbursts. We also find that the mean L_X and
L_1.4 of the faint radio sources studied here are consistent with the L_X-L_1.4
correlation of local star-forming galaxies. Moreover, the X-ray emissivity of
sub-mJy sources to z~0.3 is found to be elevated compared to local HII
galaxies. The observed increase is consistent with L_X evolution of the form
(1+z)^3. Assuming that our sample is indeed dominated by starbursts this is
direct evidence for evolution of such systems at X-ray wavelengths. Using an
empirical L_X to SFR conversion we estimate a global SFR density at z~0.3 of
\~0.029M_o/yr/Mpc in agreement with previous studies.Comment: 12 pages, 6 figures, accepted for publication in MNRA
Stellar magnetism, winds and their effects on planetary environments
Here, I review some recent works on magnetism of cool, main-sequence stars,
their winds and potential impact on surrounding exoplanets. The winds of these
stars are very tenuous and persist during their lifetime. Although carrying
just a small fraction of the stellar mass, these magnetic winds carry away
angular momentum, thus regulating the rotation of the star. Since cool stars
are likely to be surrounded by planets, understanding the host star winds and
magnetism is a key step towards characterisation of exoplanetary environments.
As rotation and activity are intimately related, the spin down of stars leads
to a decrease in stellar activity with age. As a consequence, as stars age, a
decrease in high-energy (X-ray, extreme ultraviolet) irradiation is observed,
which can a ect the evaporation of exoplanetary atmospheres and, thus, also
altering exoplanetary evolution.Comment: 6 pages, 5 figures. To appear in the proceedings of "The 19th
Cambridge Workshop on Cool Stars, Stellar Systems, and the Sun" (ed. G. A.
Feiden), Uppsala, Sweden, 06-10 June 2016. This article is based on my
invited plenary tal
The Stellar Activity - Rotation Relationship
Using a new catalog of 824 solar and late-type stars with X-ray luminosities
and rotation periods we have studied the relationship between rotation and
stellar activity. From an unbiased subset of this sample the power law slope of
the unsaturated regime, , is fit as
. This is inconsistent with the canonical slope
to a confidence of 5 and argues for an interface-type dynamo.
Super-saturation is observed for the fastest rotators in our sample and its
parametric dependencies are explored. Significant correlations are found with
both the corotation radius and the excess polar updraft, the latter theory
being supported by other observations. We also present a new X-ray population
synthesis model of the mature stellar component of our Galaxy and use it to
reproduce deep observations of a high Galactic latitude field. The model,
XStar, can be used to test models of stellar spin-down and dynamo decay, as
well as for estimating stellar X-ray contamination rates for non-stellar
studies.Comment: 4 pages, 4 figures. To appear in the proceedings of Cool Stars 17:
17th Cambridge Workshop on Cool Stars, Stellar Systems, and the Sun, AN 334,
1-2, Eds Klaus Strassmeier and Mercedes Lopez-Morale
{\it Suzaku} observation of Galactic supernova remnant CTB 37A (G348.5+0.1)
We present here the results of the observation of CTB 37A obtained with the
X-ray Imaging Spectrometer onboard the {\it Suzaku} satellite. The X-ray
spectrum of CTB 37A is well fitted by two components, a single-temperature
ionization equilibrium component (VMEKAL) with solar abundances, an electron
temperature of keV, absorbing column density of and a power-law component with photon
index of . The X-ray spectrum of CTB 37A is characterized by
clearly detected K-shell emission lines of Mg, Si, S, and Ar. The plasma with
solar abundances supports the idea that the X-ray emission originates from the
shocked interstellar material. The ambient gas density, and age of the remnant
are estimated to be and
yr, respectively. The center-filling X-ray emission
surrounded by a shell-like radio structure and other X-ray properties indicate
that this remnant would be a new member of mixed-morphology supernova remnant
class
A Tidal Disruption Flare in Abell 1689 from an Archival X-ray Survey of Galaxy Clusters
Theory suggests that a star making a close passage by a supermassive black
hole at the center of a galaxy can under most circumstances be expected to emit
a giant flare of radiation as it is disrupted and a portion of the resulting
stream of shock-heated stellar debris falls back onto the black hole itself. We
examine the first results of an ongoing archival survey of galaxy clusters
using Chandra and XMM-selected data, and report a likely tidal disruption flare
from SDSS J131122.15-012345.6 in Abell 1689. The flare is observed to vary by a
factor of >30 over at least 2 years, to have maximum L_X(0.3-3.0 keV)> 5 x
10^{42} erg s^{-1} and to emit as a blackbody with kT~0.12 keV. From the galaxy
population as determined by existing studies of the cluster, we estimate a
tidal disruption rate of 1.2 x 10^{-4} galaxy^{-1} year^{-1} if we assume a
contribution to the observable rate from galaxies whose range of luminosities
corresponds to a central black hole mass (M_bh) between 10^6 and 10^8 M_sun.Comment: 24 pages, including 6 figures and 2 tables Accepted for publication
in the Astrophysical Journa
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