268 research outputs found
The RHESSI Microflare Height Distribution
We present the first in-depth statistical survey of flare source heights
observed by RHESSI. Flares were found using a flare-finding algorithm designed
to search the 6-10 keV count-rate when RHESSI's full sensitivity was available
in order to find the smallest events (Christe et al., 2008). Between March 2002
and March 2007, a total of 25,006 events were found. Source locations were
determined in the 4-10 keV, 10-15 keV, and 15-30 keV energy ranges for each
event. In order to extract the height distribution from the observed projected
source positions, a forward-fit model was developed with an assumed source
height distribution where height is measured from the photosphere. We find that
the best flare height distribution is given by g(h) \propto exp(-h/{\lambda})
where {\lambda} = 6.1\pm0.3 Mm is the scale height. A power-law height
distribution with a negative power-law index, {\gamma} = 3.1 \pm 0.1 is also
consistent with the data. Interpreted as thermal loop top sources, these
heights are compared to loops generated by a potential field model (PFSS). The
measured flare heights distribution are found to be much steeper than the
potential field loop height distribution which may be a signature of the flare
energization process
Astrophysical Observations with the HEROES Balloon-borne Payload
The High Energy Replicated Optics to Explore the Sun (HEROES) payload flew on a balloon from Ft. Sumner, NM, September 21-22, 2013. HEROES is sensitive from about 20-75 keV and comprises 8 optics modules, each consisting of 13-14 nickel replicated optics shells and 8 Xenon-filled positionsensitive proportional counter detectors. HEROES is unique in that it is the first hard X-ray telescope that will observe the Sun and astrophysical targets in the same balloon flight. Our astrophysics targets include the Crab nebula and pulsar and the black hole binary GRS 1915+105. In this presentation, I will describe the HEROES mission, the data analysis pipeline and calibrations, and preliminary astrophysics results
The State of Self-Organized Criticality of the Sun During the Last 3 Solar Cycles. I. Observations
We analyze the occurrence frequency distributions of peak fluxes , total
fluxes , and durations of solar flares over the last three solar cycles
(during 1980--2010) from hard X-ray data of HXRBS/SMM, BATSE/CGRO, and RHESSI.
From the synthesized data we find powerlaw slopes with mean values of
for the peak flux, for the total
flux, and for flare durations. We find a systematic
anti-correlation of the powerlaw slope of peak fluxes as a function of the
solar cycle, varying with an approximate sinusoidal variation
, with a
mean of , a variation of , a solar cycle
period yrs, and a cycle minimum time . The
powerlaw slope is flattest during the maximum of a solar cycle, which indicates
a higher magnetic complexity of the solar corona that leads to an
overproportional rate of powerful flares.Comment: subm. to Solar Physic
A single hollow beam optical trap for cold atoms
We present an optical trap for atoms that we have developed for precision
spectroscopy measurements. Cold atoms are captured in a dark region of space
inside a blue-detuned hollow laser beam formed by an axicon. We analyze the
light potential in a ray optics picture and experimentally demonstrate trapping
of laser-cooled metastable xenon atoms.Comment: 12 pages, 8 figure
G(2) quivers
We present, in explicit matrix representation and a modernity befitting the community, the classification of the finite discrete subgroups of G2 and compute the McKay quivers arising therefrom. Of physical interest are the classes of Script N = 1 gauge theories descending from M-theory and of mathematical interest are possible steps toward a systematic study of crepant resolutions to smooth G2 manifolds as well as generalised McKay Correspondences. This writing is a companion monograph to hep-th/9811183 and hep-th/9905212, wherein the analogues for Calabi-Yau three- and four-folds were considered
The HEROES Balloon-Borne Hard X-Ray Telescope
The High Energy Replicated Optics to Explore the Sun (HEROES) payload flew on a balloon from Ft. Sumner, NM, September 21-22, 2013. HEROES is sensitive from about 20-75 keV and comprises 8 optics modules (HPD approximately 33" as flown), each consisting of 13-14 nickel replicated optics shells and 8 matching Xenon-filled position-sensitive proportional counter detectors (dE/E=0.05 @ 60 keV). Our targets included the Sun, the Crab Nebula and pulsar and the black hole binary GRS 1915+105. HEROES was pointed using a day/night star camera system for astrophysical observations and a newly developed Solar Aspect System for solar observations (with a shutter protecting the star camera.) We have successfully detected the Crab Nebula. Analyses for GRS 1915+105 and the Sun are ongoing. In this presentation, I will describe the HEROES mission, the data analysis pipeline and calibrations, preliminary results, and plans for follow-on missions
SuperHERO: The Next Generation Hard X-ray HEROES Telescope
SuperHERO is a new high-sensitivity Long Duration Balloon (LDB)-capable, hard-x-ray (20-75 keV) telescope for making novel astrophysics and heliophysics observations. The proposed SuperHERO payload will be developed jointly by the Astrophysics Office at NASA Marshall Space Flight Center, the Solar Physics Laboratory and Wallops Flight Facility at NASA Goddard Space Flight Center. SuperHERO is a follow-on payload to the High Energy Replicated Optics to Explore the Sun (HEROES) balloon-borne telescope that recently launched from Fort Sumner, NM in September of 2013. The HEROES core instrument is a hard x-ray telescope consisting of x-ray 109 optics configured into 8 modules. Each module is aligned to a matching gas-filled detector at a focal length of 6 m. SuperHERO will make significant improvements to the HEROES payload, including: new solid-state multi-pixel CdTe detectors, additional optics, the Wallops Arc-Second Pointer, alignment monitoring systems and lighter gondola
Thin Animals
Lattice animals provide a discretized model for the theta transition
displayed by branched polymers in solvent. Exact graph enumeration studies have
given some indications that the phase diagram of such lattice animals may
contain two collapsed phases as well as an extended phase. This has not been
confirmed by studies using other means. We use the exact correspondence between
the q --> 1 limit of an extended Potts model and lattice animals to investigate
the phase diagram of lattice animals on phi-cubed random graphs of arbitrary
topology (``thin'' random graphs). We find that only a two phase structure
exists -- there is no sign of a second collapsed phase.
The random graph model is solved in the thermodynamic limit by saddle point
methods. We observe that the ratio of these saddle point equations give
precisely the fixed points of the recursion relations that appear in the
solution of the model on the Bethe lattice by Henkel and Seno. This explains
the equality of non-universal quantities such as the critical lines for the
Bethe lattice and random graph ensembles.Comment: Latex, 10 pages plus 6 ps/eps figure
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