412 research outputs found
The Supernova Remnant G296.7-0.9 in X-rays
Aims: We present a detailed study of the supernova remnant (SNR) G296.7-0.9
in the 0.2-12 keV X-ray band.
Methods: Using data from XMM-Newton we performed a spectro-imaging analysis
of G296.7-0.9 in order to deduce the basic parameters of the remnant and to
search for evidence of a young neutron star associated with it.
Results: In X-rays the remnant is characterized by a bright arc located in
the south-west direction. Its X-ray spectrum can best be described by an
absorbed non-equilibrium collisional plasma model with a hydrogen density of
N_H=1.24_{-0.05}^{+0.07} x 10^{22} cm^{-2} and a plasma temperature of
6.2^{+0.9}_{-0.8} million Kelvin. The analysis revealed a remnant age of 5800
to 7600 years and a distance of 9.8_{-0.7}^{+1.1} kpc. The latter suggests a
spatial connection with a close-by HII region. We did not find evidence for a
young neutron star associated with the remnant.Comment: accepted by A&A, 5 pages, 2 figure
Succinct Indexable Dictionaries with Applications to Encoding -ary Trees, Prefix Sums and Multisets
We consider the {\it indexable dictionary} problem, which consists of storing
a set for some integer , while supporting the
operations of \Rank(x), which returns the number of elements in that are
less than if , and -1 otherwise; and \Select(i) which returns
the -th smallest element in . We give a data structure that supports both
operations in O(1) time on the RAM model and requires bits to store a set of size , where {\cal B}(n,m) = \ceil{\lg
{m \choose n}} is the minimum number of bits required to store any -element
subset from a universe of size . Previous dictionaries taking this space
only supported (yes/no) membership queries in O(1) time. In the cell probe
model we can remove the additive term in the space bound,
answering a question raised by Fich and Miltersen, and Pagh.
We present extensions and applications of our indexable dictionary data
structure, including:
An information-theoretically optimal representation of a -ary cardinal
tree that supports standard operations in constant time,
A representation of a multiset of size from in bits that supports (appropriate generalizations of) \Rank
and \Select operations in constant time, and
A representation of a sequence of non-negative integers summing up to
in bits that supports prefix sum queries in constant
time.Comment: Final version of SODA 2002 paper; supersedes Leicester Tech report
2002/1
The Dispersion Velocity of Galactic Dark Matter Particles
The self-consistent spatial distribution of particles of Galactic dark matter
is derived including their own gravitational potential, as also that of the
visible matter of the Galaxy. In order to reproduce the observed rotation curve
of the Galaxy the value of the dispersion velocity of the dark matter
particles, \rmsveldm, should be \sim 600\kmps or larger.Comment: RevTex, 4 pages, 1 ps figure, accepted for publication in Physical
Review Letter
A New Technique for Detecting Supersymmetric Dark Matter
We estimate the event rate for excitation of atomic transition by
photino-like dark matter. For excitations of several eV, this event rate can
exceed naive cross-section by many orders of magnitude. Although the event rate
for these atomic excitation is smaller than that of nuclear recoil off of
non-zero spin nuclei, the photons emitted by the deexcitation are easier to
detect than low-energy nuclear recoils. For many elements, there are several
low-lying states with comparable excitation rates, thus, spectral ratios could
be used to distinguish signal from background.Comment: 6 pages plain te
Far infrared mapping of three Galactic star forming regions : W3(OH), S 209 & S 187
Three Galactic star forming regions associated with W3(OH), S209 and S187
have been simultaneously mapped in two trans-IRAS far infrared (FIR) bands
centered at ~ 140 and 200 micron using the TIFR 100 cm balloon borne FIR
telescope. These maps show extended FIR emission with structures. The HIRES
processed IRAS maps of these regions at 12, 25, 60 & 100 micron have also been
presented for comparison. Point-like sources have been extracted from the
longest waveband TIFR maps and searched for associations in the other five
bands. The diffuse emission from these regions have been quantified, which
turns out to be a significant fraction of the total emission. The spatial
distribution of cold dust (T < 30 K) for two of these sources (W3(OH) & S209),
has been determined reliably from the maps in TIFR bands. The dust temperature
and optical depth maps show complex morphology. In general the dust around S209
has been found to be warmer than that in W3(OH) region.Comment: Accepted for publication in Journal of Astrophysics and Astronomy (20
pages including 8 figures & 3 tables
Exploring the supernova remnant G308.4-1.4
Aims: We present a detailed X-ray and radio wavelength study of G308.4-1.4, a
candidate supernova remnant (SNR) in the ROSAT All Sky Survey and the MOST
supernova remnant catalogue, in order to identify it as a SNR.
Methods: The SNR candidate and its central sources were studied using
observations from the Chandra X-ray Observatory, SWIFT, the Australian
Telescope Compact Array (ATCA) at 1.4 and 2.5 GHz and WISE infrared observation
at 24 m.
Results: We conclude that G308.4-1.4 is indeed a supernova remnant by means
of its morphology matching at X-ray, radio and infrared wavelength, its
spectral energy distribution in the X-ray band and its emission characteristics
in the radio band. G308.4-1.4 is a shell-type SNR. X-ray, radio and infrared
emission is seen only in the eastern part of the remnant. The X-ray emission
can best be described by an absorbed non-equilibrium collisional plasma with a
hydrogen density of cm, a
plasma temperature of million Kelvin and an under-abundance
of Iron, Neon and Magnesium, as well as an overabundance in Sulfur with respect
to the solar values. The SNR has a spectral index in the radio band of
. A detailed analysis revealed that the remnant is at a
distance of 6 to 12 kpc and the progenitor star exploded to 7500
years ago. Two faint X-ray point sources located near to the remnant's
geometrical center are detected. Both sources have no counterpart at other
wavelengths, leaving them as candidates for the compact remnant of the
supernova explosion.Comment: 12 pages, 11 figures, accepted by A&A, revised draf
N-body simulations of the Magellanic Stream
A suite of high-resolution N-body simulations of the Magellanic Clouds --
Milky Way system are presented and compared directly with newly available data
from the HI Parkes All-Sky Survey (HIPASS). We show that the interaction
between Small and Large Magellanic Clouds results in both a spatial and
kinematical bifurcation of both the Stream and the Leading Arm. The spatial
bifurcation of the Stream is readily apparent in the HIPASS data, and the
kinematical bifurcation is also tentatively identified. This bifurcation
provides strong support for the tidal disruption origin for the Magellanic
Stream. A fiducial model for the Magellanic Clouds is presented upon completion
of an extensive parameter survey of the potential orbital configurations of the
Magellanic Clouds and the viable initial boundary conditions for the disc of
the Small Magellanic Cloud. The impact of the choice of these critical
parameters upon the final configurations of the Stream and Leading Arm is
detailed.Comment: Accepted by MNRAS, 07 Jun 2006. 14 pages, 14 figures, 3 tables. LaTeX
(mn2e.sty). File with decent resolution images (strongly recommended)
available at http://astronomy.swin.edu.au/~tconnors/publications/ .
References added; distance and HI-LOres difference figures added; clearer
figures; discussion added to, but conclusions unchange
A Sino-German 6\ cm polarization survey of the Galactic plane VI. Discovery of supernova remnants G178.2-4.2 and G25.1-2.3
Supernova remnants (SNRs) were often discovered in radio surveys of the
Galactic plane. Because of the surface-brightness limit of previous surveys,
more faint or confused SNRs await discovery. The Sino-German 6\ cm
Galactic plane survey is a sensitive survey with the potential to detect new
low surface-brightness SNRs. We want to identify new SNRs from the 6\
cm survey map of the Galactic plane. We searched for new shell-like objects in
the 6\ cm survey maps, and studied their radio emission, polarization,
and spectra using the 6\ cm maps together with the 11\ cm and
21\ cm Effelsberg observations. Extended polarized objects with
non-thermal spectra were identified as SNRs. We have discovered two new, large,
faint SNRs, G178.2-4.2 and G25.1-2.3, both of which show shell structure.
G178.2-4.2 has a size of 72 arcmin x 62 arcmin with strongly polarized emission
being detected along its northern shell. The spectrum of G178.2-4.2 is
non-thermal, with an integrated spectral index of . Its
surface brightness is , which makes G178.2-4.2 the second faintest known Galactic SNR.
G25.1-2.3 is revealed by its strong southern shell which has a size of 80
arcmin x 30\arcmin. It has a non-thermal radio spectrum with a spectral index
of . Two new large shell-type SNRs have been detected at
6\ cm in an area of 2200 deg^2 along the the Galactic plane. This
demonstrates that more large and faint SNRs exist, but are very difficult to
detect.Comment: 8 pages, 8 figures, accepted by Astronomy and Astrophysics. For the
version with high resolution figures, please go to
http://zmtt.bao.ac.cn/6cm/papers/2newSNR.pd
Evidence for Dark Matter Annihilation from Galactic Gamma Rays?
The diffuse galactic EGRET gamma ray data show a clear excess for energies
above 1 GeV in comparison with the expectations from conventional galactic
models. The excess is seen with the same spectrum in all sky directions, as
expected for Dark Matter (DM) annihilation. This hypothesis is investigated in
detail. The energy spectrum of the excess is used to limit the WIMP mass to the
50-100 GeV range, while the skymaps are used to determine the halo structure,
which is consistent with a triaxial isothermal halo with additional enhancement
of Dark Matter in the disc. The latter is strongly correlated with the ring of
stars around our galaxy at a distance of 14 kpc, thought to originate from the
tidal disruption of a dwarf galaxy. It is shown that this ring of DM with a
mass of causes the mysterious change of slope
in the rotation curve at and the large local surface density of the
disc. The total mass of the halo is determined to be .
A cuspy profile is definitely excluded to describe the gamma ray data. These
signals of Dark Matter Annihilation are compatible with Supersymmetry for boost
factors of 20 upwards and have a statistical significance of more than
in comparison with the conventional galactic model. The latter
combined with all features mentioned above provides an intriguing hint that the
EGRET excess is indeed indirect evidence for Dark Matter Annihilation.Comment: To be published in Proc. of DM 2004, Feb. 2004, Los Angeles; updated
references and somewhat improved fits in new versio
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