353 research outputs found
Ni abundance in the core of the Perseus Cluster: an answer to the significance of resonant scattering
Using an XMM-Newton observation of the Perseus cluster we show that the
excess in the flux of the 7-8 keV line complex previously detected by ASCA and
BeppoSAX is due to an overabundance of Nickel rather than to an anomalously
high Fe He/Fe He ratio. This observational fact leads to the
main result that resonant scattering, which was assumed to be responsible for
the supposed anomalous Fe He/Fe He ratio, is no longer required.
The absence of resonant scattering points towards the presence of significant
gas motions (either turbulent or laminar) in the core of the Perseus cluster.Comment: 29 pages, 10 bw figures, accepted for publication in the
Astrophysical Journa
An HST/COS Observation of Broad Ly Emission and Associated Absorption Lines of the BL Lacertae Object H 2356-309
Weak spectral features in BL Lacertae objects (BL Lac) often provide a unique
opportunity to probe the inner region of this rare type of active galactic
nucleus. We present a Hubble Space Telescope/Cosmic Origins Spectrograph
observation of the BL Lac H 2356-309. A weak Ly emission line was
detected. This is the fourth detection of a weak Ly emission feature in
the ultraviolet (UV) band in the so-called "high energy peaked BL Lacs", after
Stocke et al. Assuming the line-emitting gas is located in the broad line
region (BLR) and the ionizing source is the off-axis jet emission, we constrain
the Lorentz factor () of the relativistic jet to be with a
maximum viewing angle of 3.6. The derived is somewhat larger
than previous measurements of , implying a covering
factor of 3% of the line-emitting gas. Alternatively, the BLR clouds
could be optically thin, in which case we constrain the BLR warm gas to be
. We also detected two HI and one OVI absorption
lines that are within of the BL Lac object.
The OVI and one of the HI absorbers likely coexist due to their nearly
identical velocities. We discuss several ionization models and find a
photoionization model where the ionizing photon source is the BL Lac object can
fit the observed ion column densities with reasonable physical parameters. This
absorber can either be located in the interstellar medium of the host galaxy,
or in the BLR.Comment: 7 pages, 2 figures, accepted for publication in Ap
An XMM-Newton study of the 401 Hz accreting pulsar SAX J1808.4-3658 in quiescence
SAX J1808.4-3658 is a unique source being the first Low Mass X-ray Binary
showing coherent pulsations at a spin period comparable to that of millisecond
radio pulsars. Here we present an XMM-Newton observation of SAX J1808.4-3658 in
quiescence, the first which assessed its quiescent luminosity and spectrum with
good signal to noise. XMM-Newton did not reveal other sources in the vicinity
of SAX J1808.4-3658 likely indicating that the source was also detected by
previous BeppoSAX and ASCA observations, even if with large positional and flux
uncertainties. We derive a 0.5-10 keV unabsorbed luminosity of L_X=5x10^{31}
erg/s, a relatively low value compared with other neutron star soft X-ray
transient sources. At variance with other soft X-ray transients, the quiescent
spectrum of SAX J1808.4-3658 was dominated by a hard (Gamma~1.5) power law with
only a minor contribution (<10%) from a soft black body component. If the power
law originates in the shock between the wind of a turned-on radio pulsar and
matter outflowing from the companion, then a spin-down to X-ray luminosity
conversion efficiency of eta~10^{-3} is derived; this is in line with the value
estimated from the eclipsing radio pulsar PSR J1740-5340. Within the deep
crustal heating model, the faintness of the blackbody-like component indicates
that SAX J1808.4-3658 likely hosts a massive neutronstar (M>1.7 solar masses).Comment: Paper accepted for publication in ApJ
Fossil group origins - VI. Global X-ray scaling relations of fossil galaxy clusters
We present the first pointed X-ray observations of 10 candidate fossil galaxy
groups and clusters. With these Suzaku observations, we determine global
temperatures and bolometric X-ray luminosities of the intracluster medium (ICM)
out to for six systems in our sample. The remaining four systems show
signs of significant contamination from non-ICM sources. For the six objects
with successfully determined properties, we measure global
temperatures in the range ,
bolometric X-ray luminosities of , and estimate masses,
as derived from , of .
Fossil cluster scaling relations are constructed for a sample that combines our
Suzaku observed fossils with fossils in the literature. Using measurements of
global X-ray luminosity, temperature, optical luminosity, and velocity
dispersion, scaling relations for the fossil sample are then compared with a
control sample of non-fossil systems. We find the fits of our fossil cluster
scaling relations are consistent with the relations for normal groups and
clusters, indicating fossil clusters have global ICM X-ray properties similar
to those of comparable mass non-fossil systems.Comment: 17 pages, 7 figures, 8 tables. Accepted for publication in MNRA
Dark matter-baryons separation at the lowest mass scale: the Bullet Group
We report on the X-ray observation of a strong lensing selected group, SL2S
J08544-0121, with a total mass of
which revealed a separation of kpc between the X-ray emitting
collisional gas and the collisionless galaxies and dark matter (DM), traced by
strong lensing. This source allows to put an order of magnitude estimate to the
upper limit to the interaction cross section of DM of 10 cm g. It is
the lowest mass object found to date showing a DM-baryons separation and it
reveals that the detection of bullet-like objects is not rare and confined to
mergers of massive objects opening the possibility of a statistical detection
of DM-baryons separation with future surveys.Comment: 5 pages, 3 figures. Accepted for publication in MNRAS Letters. Typos
correcte
Irregular sloshing cold fronts in the nearby merging groups NGC 7618 and UGC 12491: evidence for Kelvin-Helmholtz instabilities
We present results from two \sim30 ks Chandra observations of the hot
atmospheres of the merging galaxy groups centered around NGC 7618 and UGC
12491. Our images show the presence of arc-like sloshing cold fronts wrapped
around each group center and \sim100 kpc long spiral tails in both groups. Most
interestingly, the cold fronts are highly distorted in both groups, exhibiting
'wings' along the fronts. These features resemble the structures predicted from
non-viscous hydrodynamic simulations of gas sloshing, where Kelvin-Helmholtz
instabilities (KHIs) distort the cold fronts. This is in contrast to the
structure seen in many other sloshing and merger cold fronts, which are smooth
and featureless at the current observational resolution. Both magnetic fields
and viscosity have been invoked to explain the absence of KHIs in these smooth
cold fronts, but the NGC 7618/UGC 12491 pair are two in a growing number of
both sloshing and merger cold fronts that appear distorted. Magnetic fields
and/or viscosity may be able to suppress the growth of KHIs at the cold fronts
in some clusters and groups, but clearly not in all. We propose that the
presence or absence of KHI-distortions in cold fronts can be used as a measure
of the effective viscosity and/or magnetic field strengths in the ICM.Comment: ApJ, accepted. Uses emulateapj styl
Mapping small-scale temperature and abundance structures in the core of the Perseus cluster
We report further results from a 191 ks Chandra observation of the core of
the Perseus cluster, Abell 426. The emission-weighted temperature and abundance
structure is mapped detail. There are temperature variations down to ~1 kpc in
the brightest regions. Globally, the strongest X-ray surface brightness
features appear to be caused by temperature changes. Density and temperature
changes conspire to give approximate azimuthal balance in pressure showing that
the gas is in hydrostatic equilibrium. Si, S, Ar, Ca, Fe and Ni abundance
profiles rise inward from about 100 kpc, peaking at about 30-40 kpc. Most of
these abundances drop inwards of the peak, but Ne shows a central peak, all of
which may be explained by resonance scattering. There is no evidence for a
widespread additional cooler temperature component in the cluster with a
temperature greater than a factor of two from the local temperature. There is
however evidence for a widespread hard component which may be nonthermal. The
temperature and abundance of gas in the cluster is observed to be correlated in
a manner similar to that found between clusters.Comment: ~20 pages, colour, accepted by MNRAS. Updates include a more
extensive discussion of the hard component, reference corrections, and a few
other minor changes. A version with good figure quality is at
http://www-xray.ast.cam.ac.uk/papers/perdetail
Studying the WHIM Content of the Galaxy Large-Scale Structures along the Line of Sight to H 2356-309
We make use of a 500ks Chandra HRC-S/LETG spectrum of the blazar H2356-309,
combined with a lower S/N spectrum of the same target, to search for the
presence of warm-hot absorbing gas associated with two Large-Scale Structures
(LSSs) crossed by this sightline at z=0.062 (the Pisces-Cetus Supercluster,
PCS) and at z=0.128 ("Farther Sculptor Wall", FSW). No statistically
significant (>=3sigma) individual absorption is detected from any of the strong
He- or H-like transitions of C, O and Ne at the redshifts of the structures.
However we are still able to constrain the physical and geometrical parameters
of the associated putative absorbing gas, by performing joint spectral fit of
marginal detections and upper limits of the strongest expected lines with our
self-consistent hybrid ionization WHIM spectral model. At the redshift of the
PCS we identify a warm phase with logT=5.35_-0.13^+0.07 K and log N_H
=19.1+/-0.2 cm^-2 possibly coexisting with a hotter and less significant phase
with logT=6.9^+0.1_-0.8 K and log N_H=20.1^+0.3_-1.7 cm^-2 (1sigma errors). For
the FSW we estimate logT=6.6_-0.2^+0.1 K and log N_H=19.8_-0.8^+0.4 cm^-2. Our
constraints allow us to estimate the cumulative number density per unit
redshifts of OVII WHIM absorbers. We also estimate the cosmological mass
density obtaining Omega_b(WHIM)=(0.021^+0.031_-0.018) (Z/Z_sun)^-1, consistent
with the mass density of the intergalactic 'missing baryons' for high
metallicities.Comment: 29 pages, 8 figures, 4 tables. Accepted for publication in Ap
The late Miocene-early Pliocene biogenic bloom: an integrated study in the Tasman sea
The Late Miocene-Early Pliocene Biogenic Bloom (âŒ9â3.5 Ma) was a paleoceanographic phenomenon defined by anomalously high accumulations of biological components at multiple open ocean sites, especially in certain regions of the Indian, and Pacific oceans. Its temporal and spatial extent with available information leaves fundamental questions about driving forces and responses unanswered. In this work, we focus on the middle part of the Biogenic Bloom (7.4â4.5 Ma) at International Ocean Discovery Program Site U1506 in the Tasman Sea, where we provide an integrated age model based on orbital tuning of the Natural Gamma Radiation, benthic foraminiferal oxygen isotopes, and calcareous nannofossil biostratigraphy. Benthic foraminiferal assemblages suggest changes in deep water oxygen concentration and seafloor nutrient supply during generally high export productivity conditions. From 7.4 to 6.7 Ma, seafloor conditions were characterized by episodic nutrient supply, perhaps related to seasonal phytoplankton blooms. From 6.7 to 4.5 Ma, the regime shifted to a more stable interval characterized by eutrophic and dysoxic conditions. Combined with seismic data, a regional change in paleoceanography is inferred at around 6.7 Ma, from stronger and well-oxygenated bottom currents to weaker, oxygen-depleted bottom currents. Our results support the hypothesis that the Biogenic Bloom was a complex, multiphase phenomenon driven by changes in ocean currents, rather than a single uniform period of sustained sea surface water productivity. Highly resolved studies are thus fundamental to its understanding and the disentanglement of local, regional, and global imprints
X-ray Spectroscopy of the Core of the Perseus Cluster with Suzaku: Elemental Abundances in the Intracluster Medium
The results from Suzaku observations of the central region of the Perseus
cluster are presented. Deep exposures with the X-ray Imaging Spectrometer
provide high quality X-ray spectra from the intracluster medium. X-ray lines
from helium-like Cr and Mn have been detected significantly for the first time
in clusters. In addition, elemental abundances of Ne, Mg, Si, S, Ar, Ca, Fe,
and Ni are accurately measured within 10' (or 220 kpc) from the cluster center.
The relative abundance ratios are found to be within a range of 0.8-1.5 times
the solar value. These abundance ratios are compared with previous
measurements, those in extremely metal-poor stars in the Galaxy, and
theoretical models.Comment: 10 pages, 3 figures, accepted for ApJ
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