949 research outputs found
Diffuse Non-thermal X-ray Emission: Evidence for Cosmic-ray Acceleration at the Shock Front in IC1262
We report the first localization of diffuse, non-thermal, X-ray emission from
a nearby galaxy cluster. Using Chandra data, we have isolated a diffuse
non-thermal X-ray component with a photon index, Gamma_ X = 2.21 +0.14 -0.15
and a flux of 9.5 +1.1 -2.5 x 10^-5 photons cm^-2 s^-1 keV^-1 at 1 keV, that
extends from ~1'.5 to ~2'.5 to the south of the X-ray flux peak. Comparison to
simulations implies that the diffuse non-thermal emission is produced by
primary electrons, accelerated at shocks to relativistic velocities. Using
these results and the flux and hardness maps produced with data from the
Chandra Advanced CCD Imaging Spectrometer, we conclude that a smaller subclump
coming from the north merged with IC1262. The offset of the cD galaxy from the
X-ray peak and large peculiar velocity indicate that the subclump's impact
parameter was to the west and on the near side of IC1262.Comment: 5 pages, 4 figures, 2 tables. Accepted by ApJ
Studying the Nature of Dark Energy with Galaxy Clusters
We report on the status of our effort to constrain the nature of dark energy
through the evolution of the cluster mass function. Chandra temperature
profiles for 31 clusters from a local cluster sample are shown. The X-ray
appearance of the proto supermassive binary black hole at the center of the
cluster Abell 400 is described. Preliminary weak lensing results obtained with
Megacam@MMT for a redshift z=0.5 cluster from a distant cluster sample are
given.Comment: 5 pages, to appear in: Aschenbach, B., Burwitz, V., Hasinger, G.,
Leibundgut, B. (eds.), Relativistic Astrophysics and Cosmology - Einstein's
Legacy. ESO Astrophysics Symposia, Springer Verlag, Berlin, German
Orbital Targeting Using Reduced Eccentric Anomaly Low-Thrust Coefficients
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/90625/1/AIAA-51336-469.pd
Equivalent Average Trajectory Dynamics Using the Reduced Low-Thrust Coefficients
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/83639/1/AIAA-2010-7829-955.pd
A Soft X-ray Component in the Abell 754 Cluster
We have analyzed the Chandra, BeppoSax, and ROSAT observations of Abell 754
and report evidence of a soft, diffuse X-ray component. The emission is peaked
in the cluster center and is detected out to 8' from the X-ray center. Fitting
a thermal model to the combined BeppoSax and PSPC spectra show excess emission
below 1 keV in the PSPC and above 100 keV in the BeppoSax PDS. The source 26W20
is in the field of view of the PDS. The addition of a powerlaw with the
spectral parameters measured by Silverman et al. (1998) for 26W20 successfully
models the hard component in the PDS. The remaining excess soft emission can be
modeled by either a low temperature, 0.75 - 1.03 keV component, or by a
powerlaw with a steep spectral index, 2.3. Addition of a second thermal
component model provides a much better fit to the data than does the addition
of a non-thermal component. The Chandra temperature map does not show any
region cooler than 6.9 keV within the region where the cool component was
detected. Simulations of the emission from embedded groups were performed and
compared with the Chandra temperature map which show groups are a plausible
source of ~1 keV emission. The cool component is centrally peaked in the
cluster and the gas density and temperature are relatively high arguing against
the WHIM as the source of the X-ray emission. X-ray emission from elliptical
galaxies is not high enough to provide the total cool component luminosity,
7.0x10^43 ergs s^-1. The peak of the cool component is located between the low
frequency radio halos arguing against a non-thermal interpretation for the
emission. We conclude that emission from embedded groups is the most likely
origin of the cool component in Abell 754.Comment: Submitted to Ap
Seeking the Local Convergence Depth. V. Tully-Fisher Peculiar Velocities for 52 Abell Clusters
We have obtained I band Tully-Fisher (TF) measurements for 522 late-type
galaxies in the fields of 52 rich Abell clusters distributed throughout the sky
between 50 and 200\h Mpc. Here we estimate corrections to the data for various
forms of observational bias, most notably Malmquist and cluster population
incompleteness bias. The bias-corrected data are applied to the construction of
an I band TF template, resulting in a relation with a dispersion of 0.38
magnitudes and a kinematical zero-point accurate to 0.02 magnitudes. This
represents the most accurate TF template relation currently available.
Individual cluster TF relations are referred to the average template relation
to compute cluster peculiar motions. The line-of-sight dispersion in the
peculiar motions is 341+/-93 km/s, in general agreement with that found for the
cluster sample of Giovanelli and coworkers.Comment: 31 pages, 14 figures, uses AAS LaTeX; to appear in the Astronomical
Journa
A BeppoSAX Observation of the IC1262 Galaxy Cluster
We present an analysis of BeppoSAX observations of the IC1262 galaxy cluster
and report the first temperature and abundance measurements, along with
preliminary indications of diffuse, nonthermal emission. By fitting a 6' (~360
h_50^-1 kpc) region with a single Mewe-Kaastra-Liedahl model with photoelectric
absorption, we find a temperature of 2.1 - 2.3 keV, and abundance of 0.45 -
0.77 (both 90% confidence). We find the addition of a power-law component
provides a statistically significant improvement (F-test = 90%) to the fit. The
addition of a second thermal component also improves the fit but we argue that
it is physically implausible. The power-law component has a photon index
(Gamma_X) of 0.4 - 2.8 and a nonthermal flux of (4.1 - 56.7) x 10-5 photons
cm^-2 s^-1 over the 1.5 - 10.5 keV range in the Medium Energy Concentrator
spectrometer detector. An unidentified X-ray source found in the ROSAT High
Resolution Imager observation (~0'.9 from the center of the cluster) is a
possible explanation for the nonthermal flux; however, additional evidence of
diffuse, nonthermal emission comes from the NRAO VLA Sky Survey and the
Westerbork Northern Sky Survey radio measurements, in which excess diffuse,
radio flux is observed after point-source subtraction. The radio excess can be
fitted to a simple power law with a spectral index of ~1.8, which is consistent
with the nonthermal X-ray emission spectral index. The steep spectrum is
typical of diffuse emission and the size of the radio source implies that it is
larger than the cD galaxy and not due to a discreet source
Fatty acid 16:4(n-3) stimulates a GPR120-induced signaling cascade in splenic macrophages to promote chemotherapy resistance
Although chemotherapy is designed to eradicate tumor cells, it also has significant effects on normal tissues. The platinum-induced fatty acid 16:4(n-3) (hexadeca-4,7,10,13-tetraenoic acid) induces systemic resistance to a broad range of DNA-damaging chemotherapeutics. We show that 16:4(n-3) exerts its effect by activating splenic F4/80+/CD11blow macrophages, which results in production of chemoprotective lysophosphatidylcholines (LPCs). Pharmacologic studies, together with analysis of expression patterns, identified GPR120 on F4/80+/CD11blow macrophages as the relevant receptor for 16:4(n-3). Studies that used splenocytes from GPR120-deficient mice have confirmed this conclusion. Activation of the 16:4(n-3)-GPR120 axis led to enhanced cPLA2 activity in these splenic macrophages and secretion of the resistance-inducing lipid mediator, lysophosphatidylcholine(24:1). These studies identify a novel and unexpected function for GPR120 and suggest that antagonists of this receptor might be effective agents to limit development of chemotherapy resistance.—Houthuijzen, J. M., Oosterom, I., Hudson, B. D., Hirasawa, A., Daenen, L. G. M., McLean, C. M., Hansen, S. V. F., van Jaarsveld, M. T. M., Peeper, D. S., Jafari Sadatmand, S., Roodhart, J. M. L., van de Lest, C. H. A., Ulven, T., Ishihara, K., Milligan, G., Voest, E. E. Fatty acid 16:4(n-3) stimulates a GPR120-induced signaling cascade in splenic macrophages to promote chemotherapy resistance
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