2,087 research outputs found
RXTE Hard X-ray Observation of A754: Constraining the Hottest Temperature Component and the Intracluster Magnetic Field
Abell 754, a cluster undergoing merging, was observed in hard X-rays with the
Rossi X-ray Timing Explorer (RXTE) in order to constrain its hottest
temperature component and search for evidence of nonthermal emission.
Simultaneous modeling of RXTE data and those taken with previous missions
yields an average intracluster temperature of keV in the 1-50 keV
energy band. A multi-temperature component model derived from numerical
simulations of the evolution of a cluster undergoing a merger produces similar
quality of fit, indicating that the emission measure from the very hot gas
component is sufficiently small that it renders the two models
indistinguishable. No significant nonthermal emission was detected. However,
our observations set an upper limit of
(90% confidence limit) to the nonthermal emission flux at 20 keV. Combining
this result with the radio synchrotron emission flux we find a lower limit of
0.2 G for the intracluster magnetic field. We discuss the implications of
our results for the theories of magnetic field amplifications in cluster
mergers.Comment: Accepted for Publication in the Astrophysical Journal, 22 pages, 5
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Small scale structure and mixing at the edge of the Antarctic vortex
Small scale correlations and patterns in the chemical tracers measured from the NASA ER-2 aircraft in the 1987 AAOE campaign can be used to investigate the structure of the edge of the polar vortex and the chemically perturbed region within it. Examples of several types of transport processes can be found in the data. Since ClO and O3 have similar vertical gradients and opposite horizontal gradients near the chemically perturbed region, the correlation between ClO and O3 can be used to study the extent of horizontal transport at the edge of the chemically perturbed region. Horizontal transport dominates the correlation for a latitude band up to 4 degrees on each side of the boundary. This implies a transition zone containing a substantial fraction of the mass of the total polar vortex. Similar horizontal transport can be seen in other tracers as well. It has not been possible to distinguish reversible transport from irreversible mixing. One manifestation of the horizontal transport is that the edge of the chemically perturbed region is often layered rather than a vertical curtain. This can be seen from the frequent reversed vertical gradients of NO2, caused by air with high NO2 overlapping layers with lower mixing ratios. Water and NO2 are positively correlated within the chemically perturbed region. This is the opposite sign to the correlation in the unperturbed stratosphere. The extent of the positive correlation is too great to be attributed solely to horizontal mixing. Instead, it is hypothesized that dehydration and descent are closely connected on a small scale, possibly due to radiative cooling of the clouds that also cause ice to fall to lower altitudes
Correlation of N2O and ozone in the Southern Polar vortex during the airborne Antarctic ozone experiment
In situ N20 mixing ratios, measured by an airborne laser spectrometer (ATLAS), have been used along with in situ ozone measurements to determine the correlation of N2O and ozone in the Antarctic stratosphere during the late austral winter. During the 1987 Airborne Antarctic Ozone Experiment (AAOE), N2O data were collected by a laser absorption spectrometer on board the ER-2 on five ferry flights between Ames Research Center (37 deg N) and Punta Arenas, Chile (53 deg S), and on twelve flights over Antarctica (53 S to 72 S). Of all the trace gas species measured by instruments on board the ER-2, only one showed a relationship to the N2O/O3 correlations in the vortex. With few exceptions, positive N20/O3 correlations coincided with total water mixing ratios of greater than 2.9 ppmv, and total water mixing ratios of less than 2.9 ppmv corresponded to negative correlations. The lower water mixing ratios, or dehydrated regions, are colocated with the negative correlations within the vortex, while the wetter regions always occur near the vortex edge
X-ray Evidence for Spectroscopic Diversity of Type Ia Supernovae: XMM observation of the elemental abundance pattern in M87
We present the results of a detailed element abundance study of hot gas in
M87, observed by XMM-Newton. We choose two radial bins, 1'-3' and 8'-16'
(8'-14' for EMOS; hereafter the central and the outer zones), where the
temperature is almost constant, to carry out the detailed abundance
measurements of O, Ne, Mg, Si, S, Ar, Ca, Fe and Ni using EPIC-PN (EPN) and
-MOS (EMOS) data. First, we find that the element abundance pattern in the
central compared to the outer zone in M87 is characterized by SN Ia enrichment
of a high (roughly solar) ratio of Si-group elements (Si, S, Ar, Ca) to Fe,
implying that Si burning in SN Ia is highly incomplete. In nucleosynthesis
modeling this is associated with either a lower density of the
deflagration-detonation transition and/or lower C/O and/or lower central
ignition density and observationally detected as optically subluminous SNe Ia
in early-type galaxies. Second, we find that SN Ia enrichment has a
systematically lower ratio of the Si-group elements to Fe by 0.2 dex in the
outer zone associated with the ICM of the Virgo cluster. We find that such a
ratio and even lower values by another 0.1 dex are a characteristic of the ICM
in many clusters using observed Si:S:Fe ratios as found with ASCA. Third, the
Ni/Fe ratio in the central zone of M87 is 1.5+/-0.3 solar (meteoritic), while
values around 3 times solar are reported for other clusters. In modeling of SN
Ia, this implies a reduced influence of fast deflagration SN Ia models in the
chemical enrichment of M87's ISM. Thus, to describe the SN Ia metal enrichment
in clusters, both deflagration as well as delayed detonation scenarios are
required, supporting a similar conclusion, derived from optical studies on SNe
Ia. Abridged.Comment: 11 pages, A&A, in pres
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