1,194 research outputs found
Cross-calibration of Suzaku XIS and XMM-Newton EPIC using clusters of galaxies
We extend a previous cross-calibration study by the International
Astronomical Consortium for High Energy Calibration (IACHEC) on
XMM-Newton/EPIC, Chandra/ACIS and BeppoSAX/MECS X-ray instruments with clusters
of galaxies to Suzaku/XIS instruments. Our aim is to study the accuracy of the
energy-dependent effective area calibration of the XIS instruments by
comparison of spectroscopic temperatures, fluxes and fit residuals obtained
with Suzaku/XIS and XMM-Newton/EPIC-pn for the same cluster. The temperatures
measured in the hard 2.0-7.0 keV energy band with all instruments are
consistent within 5 %. However, temperatures obtained with the XIS instruments
in the soft 0.5-2.0 keV band disagree by 9-29 %. We investigated residuals in
the XIS soft band, which showed that if XIS0 effective area shape is accurately
calibrated, the effective areas of XIS1 and XIS3 are overestimated below 1.0
keV (or vice versa). Adjustments to the modelling of the column density of the
XIS contaminant in the 3-6 arcmin extraction region while forcing consistent
emission models in each instrument for a given cluster significantly improved
the fits. The oxygen column density in XIS1 and XIS3 contaminant must be
increased by 1-2E17 cm^-2 in comparison to the values implemented in the
current calibration, while the column density of the XIS0 contaminant given by
the analysis is consistent with the public calibration. XIS soft band
temperatures obtained with the modification to the column density of the
contaminant agree better with temperatures obtained with the EPIC-pn instrument
of XMM-Newton, than with those derived using the Chandra-ACIS instrument.
However, comparison of hard band fluxes obtained using Suzaku-XIS to fluxes
obtained using the Chandra-ACIS and EPIC-pn instruments proved inconclusive.Comment: 24 pages, 27 figures, accepted for publication in Astronomy &
Astrophysic
Suzaku observations of X-ray excess emission in the cluster of galaxies A3112
We analysed the Suzaku XIS1 data of the A3112 cluster of galaxies in order to
examine the X-ray excess emission in this cluster reported earlier with the
XMM-Newton and Chandra satellites. The best-fit temperature of the intracluster
gas depends strongly on the choice of the energy band used for the spectral
analysis. This proves the existence of excess emission component in addition to
the single-temperature MEKAL in A3112. We showed that this effect is not an
artifact due to uncertainties of the background modeling, instrument
calibration or the amount of Galactic absorption. Neither does the PSF scatter
of the emission from the cool core nor the projection of the cool gas in the
cluster outskirts produce the effect. Finally we modeled the excess emission
either by using an additional MEKAL or powerlaw component. Due to the small
differencies between thermal and non-thermal model we can not rule out the
non-thermal origin of the excess emission based on the goodness of the fit.
Assuming that it has a thermal origin, we further examined the Differential
Emission Measure (DEM) models. We utilised two different DEM models, a Gaussian
differential emission measure distribution (GDEM) and WDEM model, where the
emission measure of a number of thermal components is distributed as a
truncated power law. The best-fit XIS1 MEKAL temperature for the 0.4-7.0 keV
band is 4.7+-0.1 keV, consistent with that obtained using GDEM and WDEM models.Comment: 8 pages, 10 figures, accepted to A&
Determination of the Hubble Constant Using a Two-Parameter Luminosity Correction for Type Ia Supernovae
In this paper, we make a comprehensive determination of the Hubble constant
by using two parameters - the B-V color and the rate of decline - to simultaneously standardize the luminosities of all nearby
Cepheid-calibrated type Ia supernovae (SNe Ia) and those of a larger, more
distant sample of 29 SNe Ia. Each group is treated in as similar a manner as
possible in order to avoid systematic effects. A simultaneous
minimization yields a standardized absolute luminosity of the
Cepheid-calibrated supernovae as well as the Hubble constant obtained from the
more distant sample. We find and a standardized
absolute magnitude of -19.46. The sensitivity of to a metallicity
dependence of the Cepheid-determined distances is investigated. The total
uncertainty , dominated by uncertainties in the primary Cepheid
distance indicator, is estimated to be 5 km/s Mpc^{-1}.Comment: To appear in Ap
The Baryonic and Dark Matter Distributions in Abell 401
We combine spatially resolved ASCA temperature data with ROSAT imaging data
to constrain the total mass distribution in the cluster A401, assuming that the
cluster is in hydrostatic equilibrium. We obtain a total mass within the X-ray
core (290/h_50 kpc) of 1.2[+0.1,-0.5] 10^14 /h_50 Msun at the 90% confidence
level, 1.3 times larger than the isothermal estimate. The total mass within
r_500 (1.7/h_50 Mpc) is M_500 = 0.9[+0.3,-0.2] 10^15/ h_50 Msun at 90%
confidence, in agreement with the optical virial mass estimate, and 1.2 times
smaller than the isothermal estimate. Our M_500 value is 1.7 times smaller than
that estimated using the mass-temperature scaling law predicted by simulations.
The best fit dark matter density profile scales as r^{-3.1} at large radii,
which is consistent with the Navarro, Frenk & White (NFW) ``universal profile''
as well as the King profile of the galaxy density in A401. From the imaging
data, the gas density profile is shallower than the dark matter profile,
scaling as r^{-2.1} at large radii, leading to a monotonically increasing gas
mass fraction with radius. Within r_500 the gas mass fraction reaches a value
of f_gas = 0.21[+0.06,-0.05] h_50^{-3/2} (90% confidence errors). Assuming that
f_gas (plus an estimate of the stellar mass) is the universal value of the
baryon fraction, we estimate the 90% confidence upper limit of the cosmological
matter density to be Omega_m < 0.31.Comment: 17 pages, 6 figures, accepted by Ap
XMM-Newton and Chandra Cross Calibration Using HIFLUGCS Galaxy Clusters: Systematic Temperature Differences and Cosmological Impact
Cosmological constraints from clusters rely on accurate gravitational mass
estimates, which strongly depend on cluster gas temperature measurements.
Therefore, systematic calibration differences may result in biased,
instrument-dependent cosmological constraints. This is of special interest in
the light of the tension between the Planck results of the primary temperature
anisotropies of the CMB and Sunyaev-Zel'dovich plus X-ray cluster counts
analyses. We quantify in detail the systematics and uncertainties of the
cross-calibration of the effective area between five X-ray instruments,
EPIC-MOS1/MOS2/PN onboard XMM-Newton and ACIS-I/S onboard Chandra, and the
influence on temperature measurements. Furthermore, we assess the impact of the
cross calibration uncertainties on cosmology. Using the HIFLUGCS sample,
consisting of the 64 X-ray brightest galaxy clusters, we constrain the ICM
temperatures through spectral fitting in the same, mostly isothermal, regions
and compare them. Our work is an extension to a previous one using X-ray
clusters by the IACHEC. Performing spectral fitting in the full energy band we
find that best-fit temperatures determined with XMM-Newton/EPIC are
significantly lower than Chandra/ACIS temperatures. We demonstrate that effects
like multitemperature structure and different relative sensitivities of the
instruments at certain energy bands cannot explain the observed differences. We
conclude that using XMM-Newton/EPIC, instead of Chandra/ACIS to derive full
energy band temperature profiles for cluster mass determination results in an
8% shift towards lower OmegaM values and <1% shift towards higher sigma8 values
in a cosmological analysis of a complete sample of galaxy clusters. Such a
shift is insufficient to significantly alleviate the tension between Planck CMB
anisotropies and SZ plus XMM-Newton cosmological constraints.Comment: Accepted by A&A; Python-Script for modification of XMM-Newton/EPIC
and Chandra/ACIS effective areas according to the stacked residual ratios:
https://wikis.mit.edu/confluence/display/iachec/Data
X-ray total mass estimate for the nearby relaxed cluster A3571
We constrain the total mass distribution in the cluster A3571, combining
spatially resolved ASCA temperature data with ROSAT imaging data with the
assumption that the cluster is in hydrostatic equilibrium. The total mass
within r_500 (1.7/h_50 Mpc) is M_500 = 7.8[+1.4,-2.2] 10^14/ h_50 Msun at 90%
confidence, 1.1 times smaller than the isothermal estimate. The Navarro, Frenk
& White ``universal profile'' is a good description of the dark matter density
distribution in A3571. The gas density profile is shallower than the dark
matter profile, scaling as r^{-2.1} at large radii, leading to a monotonically
increasing gas mass fraction with radius. Within r_500 the gas mass fraction
reaches a value of f_gas = 0.19[+0.06,-0.03] h_50^{-3/2} (90% confidence
errors). Assuming that this value of f_gas is a lower limit for the the
universal value of the baryon fraction, we estimate the 90% confidence upper
limit of the cosmological matter density to be Omega_m < 0.4.Comment: 10 pages, 4 figures, accepted by Ap
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