5,903 research outputs found
The Host Galaxy of GRB980703 at Radio Wavelengths - a Nuclear Starburst in a ULIRG
We present radio observations of GRB980703 at 1.43, 4.86, and 8.46 GHz for
the period of 350 to 1000 days after the burst. These radio data clearly
indicate that there is a persistent source at the position of GRB980703 with a
flux density of approximately 70 Jy at 1.43 GHz, and a spectral index,
, where . We show that emission
from the afterglow of GRB980703 is expected to be one to two orders of
magnitude fainter, and therefore cannot account for these observations. We
interpret this persistent emission as coming from the host galaxy --- the first
example of a gamma-ray burst (GRB) host detection at radio wavelengths. We show
that emission from an AGN is unlikely, and find that it can be explained as a
result of a star-formation rate (SFR) of massive stars (M>5M) of 90
M/yr, which gives a total SFR of M/yr. Using the
correlation between the radio and far-IR (FIR) luminosities of star-forming
galaxies, we find that the host of GRB980703 is at the faint end of the class
of Ultra Luminous Infrared Galaxies (ULIRGs), with L_{FIR}\sim few\times
10^{12} L. From the radio measurements of the offset between the burst
and the host, and the size of the host, we conclude that GRB980703 occurred
near the center of the galaxy in a region of maximum star formation. A
comparison of the properties of this galaxy with radio and optical surveys at a
similar redshift () reveals that the host of GRB980703 is an
average star-forming galaxy. This result has significant implications for the
potential use of a GRB-selected galaxy sample for the study of galaxies and the
IGM at high redshifts.Comment: Submitted to Ap
SEI power source alternatives for rovers and other multi-kWe distributed surface applications
To support the Space Exploration Initiative (SEI), a study was performed to investigate power system alternatives for the rover vehicles and servicers that were subsequently generated for each of these rovers and servicers, candidate power sources incorporating various power generation and energy storage technologies were identified. The technologies were those believed most appropriate to the SEI missions, and included solar, electrochemical, and isotope systems. The candidates were characterized with respect to system mass, deployed area, and volume. For each of the missions a preliminary selection was made. Results of this study depict the available power sources in light of mission requirements as they are currently defined
Comparison of dynamic isotope power systems for distributed planet surface applications
Dynamic isotope power system (DIPS) alternatives were investigated and characterized for the surface mission elements associated with a lunar base and subsequent manned Mars expedition. System designs based on two convertor types were studied. These systems were characterized parametrically and compared over the steady-state electrical output power range 0.2 to 20 kWe. Three methods of thermally integrating the heat source and the Stirling heater head were considered, depending on unit size. Figures of merit were derived from the characterizations and compared over the parametric range. Design impacts of mission environmental factors are discussed and quantitatively assessed
Food insecurity among people with severe mental disorder in a rural Ethiopian setting: a comparative, population-based study
Aim.
In low-income African countries, ensuring food security for all segments of the population is a high priority. Mental illness is associated consistently with poverty, but there is little evidence regarding the association with food insecurity. The aim of this study was to compare the levels of food insecurity in people with severe mental disorders (SMD) with the general population in a rural African setting with a high burden of food insecurity.
Method.
Households of 292 community-ascertained people with a specialist-confirmed diagnosis of SMD (including schizophrenia and bipolar disorder) were compared with 284 households without a person with SMD in a rural district in south Ethiopia. At the time of the study, no mental health services were available within the district. Food insecurity was measured using a validated version of the Household Food Insecurity Access Scale. Disability was measured using the World Health Organisation Disability Assessment Schedule 2.0.
Result.
Severe household food insecurity was reported by 32.5% of people with SMD and 15.9% of respondents from comparison households: adjusted odds ratio 2.82 (95% confidence interval 1.62 to 4.91). Higher annual income was associated independently with lower odds of severe food insecurity. When total disability scores were added into the model, the association between SMD and food insecurity became non-significant, indicating a possible mediating role of disability.
Conclusion.
Efforts to alleviate food insecurity need to target people with SMD as a vulnerable group. Addressing the disabling effects of SMD would also be expected to reduce food insecurity. Access to mental health care integrated into primary care is being expanded in this district as part of the Programme for Improving Mental health carE (PRIME). The impact of treatment on disability and food insecurity will be evaluated
COMPTEL measurements of MeV gamma-ray burst spectra
We present results from the on-going spectral analysis of gamma-ray bursts measured by the COMPTEL instrument in its main Compton âTelescopeâ observing mode (0.75â30 MeV). Thus far, 18 bursts have been analyzed from three years (April 1991âApril 1994) of observations. The time-averaged spectra of these events above 1 MeV are all consistent with a simple power law model with spectral index in the range 1.5â3.5. Exponential, thermal bremsstrahlung and thermal synchrotron models are statistically inconsistent with the burst sample, although they can adequately describe some of the individual burst spectra. We find good agreement between burst spectra measured simultaneously by BATSE, COMPTEL and EGRET, which typically show a spectral transition or âbreakâ in the BATSE energy range around a few hundred keV followed by simple power law emission extending to hundreds of MeV. However, the temporal relation between MeV and GeV (e.g., as measured by EGRET) burst emission is still unclear. Measurement of rapid variability at MeV energies in the stronger bursts provides evidence that either the sources are nearby (within the Galaxy) or the gamma-ray emission is relativistically beamed
Challenges and opportunities to improve autism services in low-income countries: lessons from a situational analysis in Ethiopia
Background.
Little has been reported about service provision for children with autism in low-income countries. This study explored the current service provision for children with autism and their families in Ethiopia, the existing challenges and urgent needs, and stakeholdersâ views on the best approaches to further develop services.
Methods.
A situational analysis was conducted based on i) qualitative interviews with existing service providers; ii) consultation with a wider group of stakeholders through two stakeholder workshops; and iii) information available in the public domain. Findings were triangulated where possible.
Results.
Existing diagnostic and educational services for children with autism are scarce and largely confined to Ethiopiaâs capital city, with little provision in rural areas. Families of children with autism experience practical and psychosocial challenges, including severe stigma. Informants further raised the lack of culturally and contextually appropriate autism instruments as an important problem to be addressed. The study informants and local stakeholders provided several approaches for future service provision expansion, including service decentralisation, mental health training and awareness raising initiatives.
Conclusions.
Services for children with autism in Ethiopia are extremely limited; appropriate care for these children is further impeded by stigma and lack of awareness. Ethiopiaâs plans to scale up mental healthcare integrated in primary healthcare provides an opportunity to expand services for children with autism and other developmental disorders. These plans and additional strategies outlined in this paper can help to address the current service provision gaps and may also inform service enhancement approaches in other low-income countries
The angular distribution of COMPTEL Gamma-Ray bursts
The superior burst location capability of the COMPTEL instrument aboard the Compton Gamma-Ray Observatory allows us to study the small-scale angular distribution of burst sources with good sensitivity even though the number of burst detections is small. We accumulate four years (April 1991âApril 1995) of observations to form a catalog of 27 burst locations whose mean 1Ď uncertainty is âź1°. We find that the COMPTEL bursts are consistent with an isotropic distribution of sources, yet the spatial coincidence of two of the bursts within COMPTELâs angular resolution indicates the possibility of repetition. This possibility is studied using the two-point angular correlation function and the nearest neighbor statistic. Model dependent upper limits on the fraction of repeating sources are derived
BATSE Observations of Gamma-Ray Burst Spectra. IV. Time-Resolved High-Energy Spectroscopy
We report on the temporal behavior of the high-energy power law continuum
component of gamma-ray burst spectra with data obtained by the Burst and
Transient Source Experiment. We have selected 126 high fluence and high flux
bursts from the beginning of the mission up until the present. Much of the data
were obtained with the Large Area Detectors, which have nearly all-sky
coverage, excellent sensitivity over two decades of energy and moderate energy
resolution, ideal for continuum spectra studies of a large sample of bursts at
high time resolution. At least 8 spectra from each burst were fitted with a
spectral form that consisted of a low-energy power law, a spectral break at
middle energies and a high-energy continuum. In most bursts (122), the
high-energy continuum was consistent with a power law. The evolution of the
fitted high-energy power-law index over the selected spectra for each burst is
inconsistent with a constant for 34% of the total sample. The sample
distribution of the average value for the index from each burst is fairly
narrow, centered on -2.12. A linear trend in time is ruled out for only 20% of
the bursts, with hard-to-soft evolution dominating the sample (100 events). The
distribution for the total change in the power-law index over the duration of a
burst peaks at the value -0.37, and is characterized by a median absolute
deviation of 0.39, arguing that a single physical process is involved. We
present analyses of the correlation of the power-law index with time, burst
intensity and low-energy time evolution. In general, we confirm the general
hard-to-soft spectral evolution observed in the low-energy component of the
continuum, while presenting evidence that this evolution is different in nature
from that of the rest of the continuum.Comment: 30 pages, with 2 tables and 9 figures To appear in The Astrophysical
Journal, April 1, 199
First results of the BATSE/COMPTEL/NMSU rapid burst response campaign
The Imaging Compton Telescope (COMPTEL) on board the Compton Gamma Ray Observatory regularly observes gammaâray bursts which occur inside the instrumentâs âź1 sr fieldâofâview. COMPTEL images bursts in the 0.75â30 MeV energy range with a typical location accuracy of 1â3 degrees, depending on burst strength, position, duration, and spectrum. COMPTELâs imaging capability has been exploited in order to search for fading gammaâray burst counterparts at other wavelengths through the establishment of a BATSE/COMPTEL/NMSU rapid burst response campaign. This campaign utilizes near realâtime identification and preliminary burst location by BATSE, accelerated COMPTEL imaging, and a worldâwide network of observers to search COMPTEL error boxes as quickly as possible. Timely, deep searches for lingering counterpart emission of several bursts per year are the realized goal of this campaign. During its first year of operation, the rapid response program has been successfully applied to two strong bursts: GRB 930131 and GRB 930309. These bursts were imaged in record time only hours after their occurrence. Subsequently, several observations were made at radio and optical observatories worldâwide
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