6,482 research outputs found
A candidate gamma-ray pulsar in the supernova remnant CTA 1
We present a detailed analysis of the high energy gamma-ray source 2EG
J0008+7307. The source has a steady flux and a hard spectrum, softening above 2
GeV. The properties of the gamma-ray source are suggestive of emission from a
young pulsar in the spatially coincident CTA 1 supernova remnant, which has
recently been found to have a non-thermal X-ray plerion. Our 95% uncertainty
contour around the >1 GeV source position includes the point-like X-ray source
at the centre of the plerion. We propose that this object is a young pulsar and
is the most likely counterpart of 2EG J0008+7307.Comment: Accepted for publication in MNRAS. 6 pages including four PS figures.
Uses mn.te
Market Segmentation Practices of Retail Crop Input Firms
The farmers targeted by crop input retailers may be divided into distinct groups or segments, but retail crop input firms vary in their ability to implement strategies to serve individual segments. In this study, segmentation practices among cooperatives and independently owned crop input retailers were explored. Addressing gaps between Best’s seven-step market segmentation framework and retailer practices will help practitioners serve evolving farmer-customers.market segmentation, target marketing, crop inputs, distribution channel, retailer, Marketing, Q10, Q13,
OTV bearing deflection investigation
The primary goal of the Bearing Deflectometer Investigation was to gain experience in the use of fiber optic displacement probe technology for bearing health monitoring in a liquid hydrogen turbo pump. The work specified in this Task Order was conducted in conjunction with Air Force Rocket Propulsion Laboratory Contract F04611-86-C-0010. APD conducted the analysis and design coordination to provide a displacement probe design compatible with the XLR-134 liquid hydrogen turbo pump assembly (TPA). Specifications and requirements of the bearing deflectometer were established working with Mechanical Technology Instruments, Inc. (MTI). The TPA design accommodated positioning of the probe to measure outer race cyclic deflections of the pump inlet bearing. The fiber optic sensor was installed as required in the TPA and sensor output was recorded during the TPA testing. Data review indicated that no bearing deflection signature could be differentiated from the inherent system noise. Alternate sensor installations were not investigated, but might yield different results
Positional Coincidence between the High-latitude Steady Unidentified Gamma-ray Sources and Possibly Merging Clusters of Galaxies
We report an evidence for the first time that merging clusters of galaxies
are a promising candidate for the origin of high galactic-latitude, steady
unidentified EGRET gamma-ray sources. Instead of using past optical catalogs of
eye-selected clusters, we made a matched-filter survey of galaxy clusters over
4\arcdeg \times 4\arcdeg areas around seven steady unidentified EGRET sources
at |b|>45\arcdeg together with a 100 \sq \arcdeg area near the South
Galactic Pole as a control field. In total, 154 Abell-like cluster candidates
and 18 close pairs/groups of these clusters, expected to be possibly merging
clusters, were identified within estimated redshift . Five
among the seven EGRET sources have one or two cluster pairs/groups (CPGs)
within 1\arcdeg from them. We assess the statistical significance of this
result by several methods, and the confidence level of the real excess is
maximally 99.8% and 97.8% in a conservative method. In contrast, we found no
significant correlation with single clusters. In addition to the spatial
correlation, we also found that the richness of CPGs associated with EGRET
sources is considerably larger than those of CPGs in the control field. These
results imply that a part of the steady unidentified EGRET sources at
high-latitude are physically associated with close CPGs, not with single
clusters. We also discuss possible interpretations of these results. We argue
that, if these associations are real, they are difficult to explain by hadronic
processes, but best explained by the inverse-Compton scattering by high energy
electrons accelerated in shocks of cluster formation, as recently proposed.Comment: 9 pages, 2 PostScript figures, uses emulateapj5.sty, added new
analysis and discussion, ApJ accepte
BL Lac Contribution to the Extragalactic Gamma-Ray Background
Very high energy gamma-rays from blazars traversing cosmological distances
through the metagalactic radiation field can convert into electron-positron
pairs in photon-photon collisions. The converted gamma-rays initiate
electromagnetic cascades driven by inverse-Compton scattering off the microwave
background photons. Using a model for the time-dependent metagalactic radiation
field consistent with all currently available far-infrared-to-optical data, we
calculate the cascade contribution from faint, unresolved high- and low-peaked
blazars to the extragalactic gamma-ray background as measured by EGRET. For
low-peaked blazars, we adopt a spectral index consistent with the mean spectral
index of EGRET detected blazars, and the luminosity function determined by
Chiang and Mukherjee (1998). For high-peaked blazars, we adopt template spectra
matching prototype sources observed with air-Cherenkov telescopes up to 30 TeV,
and a luminosity function based on X-ray measurements. The low number of about
20 for nearby high-peaked blazars with a flux exceeding 10^-11 cm^-2 s^-1 above
300 GeV inferred from the luminosity function is consistent with the results
from air-Cherenkov telescope observations. Including the cascade emission from
higher redshifts, the total high-peaked blazar contribution to the observed
gamma-ray background at GeV energies can account up to about 30.Comment: 8 pages, 7 figures, accepted by A&A, final versio
Chasing the second gamma-ray bright isolated neutron star: 3EG J1835+5918/RX J1836.2+5925
The EGRET telescope aboard NASAs Compton GRO has repeatedly detected 3EG
J1835+5918, a bright and steady source of high-energy gamma-ray emission with
no identification suggested until recently. The long absence of any likely
counterpart for a bright gamma-ray source located 25 degrees off the Galactic
plane initiated several attempts of deep observations at other wavelengths. We
report on counterparts in X-rays on a basis of a 60 ksec ROSAT HRI image. In
order to conclude on the plausibility of the X-ray counterparts, we reanalyzed
data from EGRET at energies above 100 MeV and above 1 GeV, including data up to
CGRO observation cycle 7. The gamma-ray source location represents the latest
and probably the final positional assessment based on EGRET data. The X-ray
counterparts were studied during follow-up optical identification campaigns,
leaving only one object to be likely associated with the gamma-ray source 3EG
J1835+5918. This object, RX J1836.2+5925, has the characteristics of an
isolated neutron star and possibly of a radio-quiet pulsar.Comment: 5 pages, 3 figures. To appear in the Proceedings of the 270.
WE-Heraeus Seminar on Neutron Stars, Pulsars and Supernova Remnants, Jan.
21-25, 2002, Physikzentrum Bad Honnef, eds W. Becker, H. Lesch & J. Truemper.
Proceedings are available as MPE-Report 27
AVIRIS ground data-processing system
The Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) has been under development at JPL for the past four years. During this time, a dedicated ground data-processing system has been designed and implemented to store and process the large amounts of data expected. This paper reviews the objectives of this ground data-processing system and describes the hardware. An outline of the data flow through the system is given, and the software and incorporated algorithms developed specifically for the systematic processing of AVIRIS data are described
- …