2,830 research outputs found
Non-linear shock acceleration and high energy gamma rays from clusters of galaxies
Merger and accretion shocks in clusters of galaxies can accelerate particles
via first order Fermi process. Since this mechanism is believed to be
intrinsically efficient, shocks are expected to be modified by the backreaction
of the accelerated particles. Such a modification might induce appreciable
effects on the non--thermal emission from clusters and a suppression of the
heating of the gas at strong shocks. Here we consider in particular the gamma
ray emission and we discuss the capability of Cherenkov telescopes such as HESS
to detect clusters at TeV energies.Comment: 6 pages, to appear in the proceedings of the Gamma 2004 Symposium on
High Energy Gamma Ray Astronomy, Heidelberg, July 2004 (AIP Proceedings
Series
Electron Energy Distributions at Relativistic Shock Sites: Observational Constraints from the Cygnus A Hotspots
We report new detections of the hotspots in Cygnus A at 4.5 and 8.0 microns
with the Spitzer Space Telescope. Together with detailed published radio
observations and synchrotron self-Compton modeling of previous X-ray
detections, we reconstruct the underlying electron energy spectra of the two
brightest hotspots (A and D). The low-energy portion of the electron
distributions have flat power-law slopes (s~1.5) up to the break energy which
corresponds almost exactly to the mass ratio between protons and electrons; we
argue that these features are most likely intrinsic rather than due to
absorption effects. Beyond the break, the electron spectra continue to higher
energies with very steep slopes s>3. Thus, there is no evidence for the
`canonical' s=2 slope expected in 1st order Fermi-type shocks within the whole
observable electron energy range. We discuss the significance of these
observations and the insight offered into high-energy particle acceleration
processes in mildly relativistic shocks.Comment: 5 pages, 3 figures, in Extragalactic Jets: Theory and Observation
from Radio to Gamma Ray, Eds. T. A. Rector and D. S. De Youn
Chain Match: An Algorithm for Finding a Perfect Matching of a Regular Bipartite Multigraph
We consider the problem of performing an edge coloring of a d-regular bipartite multigraph G = (V, E). While an edge coloring can be found by repeatedly performing Euler partitions on G, doing so requires that the degree of G be a power of 2. One way to allow the Euler partitioning method to continue in cases where d is not a power of 2 is to remove a perfect matching from the graph after any partition that results in a graph with an odd degree. If this perfect matching can be identified in O(E) time, we can maintain the best case runtime for this coloring of O(E lg d). This paper presents Chain Match, an algorithm that finds a perfect matching in a d-regular bipartite multigraph. While we have proven that Chain Match will always terminate with a perfect matching, we have not been able to implement it within our goal runtime of O(E)
Analyzing Big Cat Behaviors in an Artificial Environment
The purpose of this research is, to observe big cat behaviors at The Exotic Feline Rescue Center, and analyze these behaviors in comparison to known behaviors, to see the affects an artificial environment has on these cats. In this study the term artificial environment refers to anything outside of the natural habitat. The behaviors studied include: aggressive territory behaviors, feeding behaviors and communication behaviors. The behaviors were studied in Tigers, Lions, Cougars and Bobcats. These cats were studied during feeding, while on tours, and while doing normal walk-arounds.
The results of this study show cats in captivity do exhibit similar behaviors to those exhibited in the wild, though the behaviors may be displayed for different reasons. The cats at the Exotic Feline Rescue Center rely on the keepers for food and other necessities and receive plenty of attention from volunteers and visitors. Because of this, these cats are used to interacting with humans and may use many of their behaviors to get attention
Discovery of hard X-ray features around hotspots of Cygnus A
We present results of analysis of a Chandra observation of Cygnus A in which
the X-ray hotspots at the ends of the jets are mapped in detail. A hardness map
reveals previously unknown structure in the form of outer and inner hard arcs
around the hotspots, with hardness significantly enhanced compared with the
hotspot central regions. The outer hard arcs may constitute the first detection
of the bow shock; the inner hard arcs may reveal where the jets impact on the
hotspots. We argue that these features cannot result from electrons radiating
by the synchrotron self-Compton process. Instead we consider two possible
sources of the hard emission: the outer arcs may be due to thermal radiation of
hot intracluster gas compressed at the bow shock. Alternatively, both outer and
inner arcs may be due to synchrotron radiation of electrons accelerated in
turbulent regions highly perturbed by shocks and shear flows. Comparison of
measured hardness ratios with simulations of the hardness ratios resulting from
these processes show that it is more diffcult to explain the observations with
a thermal model. Although we cannot rule out a thermal model, we argue in
favour of the non-thermal explanation. The hard regions in the secondary
hotspots suggest that jet activity is still powering these hotspots.Comment: MNRAS in press; 5 pages, 3 figures (2 figures in colour in jpeg
format should be printed separately
Dynamics and High Energy Emission of the Flaring HST-1 Knot in the M 87 Jet
Stimulated by recent observations of a radio-to-X-ray synchrotron flare from
HST-1, the innermost knot of the M 87 jet, as well as by a detection of a very
high energy gamma-ray emission from M 87, we investigated the dynamics and
multiwavelength emission of the HST-1 region. We study thermal pressure of the
hot interstellar medium in M 87 and argue for a presence of a gaseous
condensation in its central parts. Interaction of the jet with such a feature
is likely to result in formation of a converging reconfinement shock in the
innermost parts of the M 87 jet. We show that for a realistic set of the
outflow parameters, a stationary and a flaring part of the HST-1 knot located
\~100 pc away from the active center can be associated with the decelerated
portion of the jet matter placed immediately downstream of the point where the
reconfinement shock reaches the jet axis. We discuss a possible scenario
explaining a broad-band brightening of the HST-1 region related to the variable
activity of the central core. We show that assuming a previous epoch of the
high central black hole activity resulting in ejection of excess particles and
photons down along the jet, one may first expect a high-energy flare of HST-1
due to inverse-Comptonisation of the nuclear radiation, followed after a few
years by an increase in the synchrotron continuum of this region. If this is
the case, then the recently observed increase in the knot luminosity in all
spectral bands could be regarded as an unusual echo of the outburst that had
happened previously in the active core of the M 87 radio galaxy.Comment: 30 pages, 7 figures included. Accepted for publication in MNRA
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