562 research outputs found
Limits on Supersymmetric Dark Matter From EGRET Observations of the Galactic Center Region
In most supersymmetic models, neutralino dark matter particles are predicted
to accumulate in the Galactic center and annihilate generating, among other
products, gamma rays. The EGRET experiment has made observations in this
region, and is sensitive to gamma rays from 30 MeV to 30 GeV. We have
used an improved point source analysis including an energy dependent point
spread function and an unbinned maximum likelihood technique, which has allowed
us to significantly lower the limits on gamma ray flux from the Galactic
center. We find that the present EGRET data can limit many supersymmetric
models if the density of the Galactic dark matter halo is cuspy or spiked
toward the Galactic center. We also discuss the ability of GLAST to test these
models.Comment: 4 pages, 3 figure
The Gamma Ray Burst section of the White Paper on the Status and Future of Very High Energy Gamma Ray Astronomy: A Brief Preliminary Report
Original paper can be found at: http://proceedings.aip.org/proceedings/ Copyright American Institute of Physics DOI: 10.1063/1.2943545otherPeer reviewe
A Search for Ultra-High Energy Counterparts to Gamma-Ray Bursts
A small air shower array operating over many years has been used to search
for ultra-high energy (UHE) gamma radiation ( TeV) associated with
gamma-ray bursts (GRBs) detected by the BATSE instrument on the Compton
Gamma-Ray Observatory (CGRO). Upper limits for a one minute interval after each
burst are presented for seven GRBs located with zenith angles . A excess over background was observed between 10 and
20 minutes following the onset of a GRB on 11 May 1991. The confidence level
that this is due to a real effect and not a background fluctuation is 99.8\%.
If this effect is real then cosmological models are excluded for this burst
because of absorption of UHE gamma rays by the intergalactic radiation fields.Comment: 4 pages LaTeX with one postscript figure. This version does not use
kluwer.sty and will allow automatic postscript generatio
Gamma-Ray Bursts: Progress, Problems & Prospects
The cosmological gamma-ray burst (GRB) phenomenon is reviewed. The broad
observational facts and empirical phenomenological relations of the GRB prompt
emission and afterglow are outlined. A well-tested, successful fireball shock
model is introduced in a pedagogical manner. Several important uncertainties in
the current understanding of the phenomenon are reviewed, and prospects of how
future experiments and extensive observational and theoretical efforts may
address these problems are discussed.Comment: 86 pages, 17 figures, 566 references, an invited review for
International Journal of Modern Physics A, in pres
Section on Prospects for Dark Matter Detection of the White Paper on the Status and Future of Ground-Based TeV Gamma-Ray Astronomy
This is a report on the findings of the dark matter science working group for
the white paper on the status and future of TeV gamma-ray astronomy. The white
paper was commissioned by the American Physical Society, and the full white
paper can be found on astro-ph (arXiv:0810.0444). This detailed section
discusses the prospects for dark matter detection with future gamma-ray
experiments, and the complementarity of gamma-ray measurements with other
indirect, direct or accelerator-based searches. We conclude that any
comprehensive search for dark matter should include gamma-ray observations,
both to identify the dark matter particle (through the charac- teristics of the
gamma-ray spectrum) and to measure the distribution of dark matter in galactic
halos.Comment: Report from the Dark Matter Science Working group of the APS
commissioned White paper on ground-based TeV gamma ray astronomy (19 pages, 9
figures
TeV Gamma-Ray Sources from a Survey of the Galactic Plane with Milagro
A survey of Galactic gamma-ray sources at a median energy of ~20 TeV has been
performed using the Milagro Gamma Ray Observatory. Eight candidate sources of
TeV emission are detected with pre-trials significance in the
region of Galactic longitude and latitude
. Four of these sources, including the Crab nebula
and the recently published MGRO J2019+37, are observed with significances
after accounting for the trials involved in searching the 3800
square degree region. All four of these sources are also coincident with EGRET
sources. Two of the lower significance sources are coincident with EGRET
sources and one of these sources is Geminga. The other two candidates are in
the Cygnus region of the Galaxy. Several of the sources appear to be spatially
extended. The fluxes of the sources at 20 TeV range from ~25% of the Crab flux
to nearly as bright as the Crab.Comment: Submitted to Ap
Criticality and Superfluidity in liquid He-4 under Nonequilibrium Conditions
We review a striking array of recent experiments, and their theoretical
interpretations, on the superfluid transition in He in the presence of a
heat flux, . We define and evaluate a new set of critical point exponents.
The statics and dynamics of the superfluid-normal interface are discussed, with
special attention to the role of gravity. If is in the same direction as
gravity, a self-organized state can arise, in which the entire sample has a
uniform reduced temperature, on either the normal or superfluid side of the
transition. Finally, we review recent theory and experiment regarding the heat
capacity at constant . The excitement that surrounds this field arises from
the fact that advanced thermometry and the future availability of a
microgravity experimental platform aboard the International Space Station will
soon open to experimental exploration decades of reduced temperature that were
previously inaccessible.Comment: 16 pages, 9 figures, plus harvard.sty style file for references
Accepted for publication in Colloquia section of Reviews of Modern Physic
- …