186 research outputs found
GeV Emission from Prompt and Afterglow Phases of Gamma-Ray Bursts
We investigate the GeV emission from gamma-ray bursts (GRBs), using the
results from the Energetic Gamma Ray Experimental Telescope (EGRET), and in
view of the Gamma-ray Large Area Space Telescope (GLAST). Assuming that the
conventional prompt and afterglow photons originate from synchrotron radiation,
we compare an accompanying inverse-Compton component with EGRET measurements
and upper limits on GeV fluence, taking Klein-Nishina feedback into account. We
find that EGRET constraints are consistent with the theoretical framework of
the synchrotron self-Compton model for both prompt and afterglow phases, and
discuss constraints on microphysical parameters in both phases. Based on the
inverse-Compton model and using EGRET results, we predict that GLAST would
detect GRBs with GeV photons at a rate >~20 yr^{-1} from each of the prompt and
afterglow phases. This rate applies to the high-energy tail of the prompt
synchrotron emission and to the inverse-Compton component of the afterglow.
Theory predicts that in a large fraction of the cases where synchrotron GeV
prompt emission would be detected by GLAST, inverse-Compton photons should be
detected as well at high energies >~10 GeV. Therefore GLAST will enable a more
precise test of the high-energy emission mechanism. Finally, we show that the
contribution of GRBs to the flux of the extragalactic gamma-ray background
measured with EGRET is at least 0.01% and likely around 0.1%.Comment: 11 pages, 7 figures; accepted by Ap
Evidence for Post-Quiescent, High-Energy Emission from Gamma-Ray Burst 990104
It is well known that high-energy emission (MeV-GeV) has been observed in a
number of gamma-ray bursts, and temporally-extended emission from lower energy
gamma rays through radio wavelengths is well established. An important observed
characteristic of some bursts at low energy is quiescence: an initial emission
followed by a quiet period before a second (postquiescent) emission. Evidence
for significant high-energy, postquiescent emission has been lacking. Here we
present evidence for high-energy emission, coincident with lower energy
emission, from the postquiescent emission episode of the very bright and long
burst, GRB 990104. We show light curves and spectra that confirm emission above
50 MeV, approximately 152 seconds after the BATSE trigger and initial emission
episode. Between the initial emission episode and the main peak, seen at both
low and high energy, there was a quiescent period of ~100 s during which the
burst was relatively quiet. This burst was found as part of an ongoing search
for high-energy emission in gamma-ray bursts using the EGRET fixed interval (32
s) accumulation spectra, which provide sensitivity to later, high-energy
emission that is otherwise missed by the standard EGRET BATSE-triggered burst
spectra.Comment: 5 pages, including 5 figures. Missing citation added to introduction.
Accepted for publication in ApJ
Os efeitos do distanciamento social sobre a frequência alimentar e o estilo de vida de moradores do Rio Grande do Sul / The effects social distancing about food frequency and lifestyle of residents of Rio Grande do Sul
A pandemia causada pelo COVID-19 afetou o estilo de vida da população mundial, principalmente devido às políticas de distanciamento social adotadas. O objetivo dessa pesquisa transversal é avaliar a frequência do consumo alimentar e os hábitos de vida de moradores com mais de 18 anos do Rio Grande do Sul, durante a pandemia causada pelo COVID-19 através de um questionário online. Foram coletadas informações sobre frequência alimentar, atividade física, número de lanches entre refeições, horas de sono, costume de cozinhar e hábito de fumar antes e durante o período de distanciamento social. As variáveis numéricas foram comparadas com teste t de Student ou Wilcoxon. As variáveis categóricas foram comparadas utilizando-se o teste de McNemar. Participaram da pesquisa 369 gaúchos, sendo 76,8 % do sexo feminino. Em relação ao início da pandemia, os participantes referiram um aumento significativo no consumo de vegetais (p = 0,005) e frutas (p = 0,029) e uma diminuição significativa no consumo de laticínios (p < 0,001), carnes (p = 0,010), doces (p = 0,013) e produtos ultraprocessados (p = 0,008). A média do IMC referido dos participantes também aumentou (p < 0,001), enquanto os dias de práticas de atividade física reduziram (p < 0,001) durante o período de distanciamento social. O estudo mostra que as restrições impostas pela pandemia podem afetar a frequência alimentar e o estilo de vida da população
Pair Production Absorption Troughs in Gamma-Ray Burst Spectra: A Potential Distance Discriminator
Relativistic bulk motion with large Lorentz factors has recently been
inferred for gamma-ray bursts regardless of whether they are of galactic or
cosmological origin. This conclusion results from calculations of internal pair
production transparency in bursts that usually assume an infinite power-law
source spectrum for simplicity, an approximation that is quite adequate for
some bursts detected by EGRET. However, for a given bulk Lorentz factor
\teq{\Gamma}, photons above the EGRET range can potentially interact with
sub-MeV photons in such calculations. Hence it is essential to accurately
address the spectral curvature in bursts seen by BATSE. In this paper we
present the major properties induced in photon-photon opacity considerations by
such spectral curvature. The observed spectral breaks around 1 MeV turn out to
be irrelevant to opacity in cosmological bursts, but are crucial to estimates
of source transparency in the 1 GeV -- 1 TeV range for sources located in the
galactic halo. We find that broad absorption troughs can arise at these
energies for suitable bulk motion parameters \teq{\Gamma}. Such troughs are
probably an unambiguous signature of a galactic halo population, and if
observed by experiments such as Whipple, MILAGRO and GLAST, would provide
powerful evidence that such bursts are not at cosmological distances.Comment: 10 pages, AASTeX format, including 2 eps figures, ApJLett in pres
Estimating the Importance of Civil Construction for the Brazilian Economy Through Hypothetical Extraction of the Input-Output Matrix
This paper aims to undertake a systemic analysis of civil construction to verify whether public investments made from 2007 onwards were able to increase the sector's productive linkages in the Brazilian economy. For this, the hypothetical extraction method of the input-output matrix and the official matrices of the country from 2005 and 2015 are used. The results show that the importance of the productive structure of the construction sector - total extraction - exceeds 7.42% of GDP in 2005 to 10.06% in 2015. This fact reveals that the civil construction sector in 2005 was the seventh most important moving to the fourth in 2015 in a total of twelve sectors considered. Another important finding lies in the fact that despite the construction sector presenting an increase in the complexity of its productive structure, it showed strong backward linkage, but low forward linkage, in both analyzed periods. Through these results, it is possible to conclude that the tax exemption of some inputs, reduction of real estate interest, expansion of credit for housing through public housing and infrastructure policies may have been essential for the increase in the complexity of the sector's productive chains between the years' from 2005 and 2015. Such findings are useful for the scientific literature that investigates the sector by bringing evidence to Brazil and to policymakers given that possibly the construction sector can be used as a strategy to promote and stimulate economic activity in times of crisis
EGRET Spectral Index and the Low-Energy Peak Position in the Spectral Energy Distribution of EGRET-Detected Blazars
In current theoretical models of the blazar subclass of active galaxies, the
broadband emission consists of two components: a low-frequency synchrotron
component with a peak in the IR to X-ray band, and a high-frequency inverse
Compton component with a peak in the gamma-ray band. In such models, the
gamma-ray spectral index should be correlated with the location of the
low-energy peak, with flatter gamma-ray spectra expected for blazars with
synchrotron peaks at higher photon energies and vice versa. Using the
EGRET-detected blazars as a sample, we examine this correlation and possible
uncertainties in its construction.Comment: 17 pages including 1 figure, accepted for publication in The
Astrophysical Journa
Future of work in the Brazilian Federal District's executive branch
Neste artigo, abordamos o tema ‘Futuro do Trabalho’ com foco no setor público do Distrito Federal brasileiro. O Brasil é uma república federativa e o ente federado em questão possui o oitavo maior PIB entre os 27 entes federados brasileiros (26 estados e o Distrito Federal). Por ser a sede do poder executivo federal, o Distrito Federal apresenta o maior PIB per capita, quase o dobro do vice-campeão, justificando a importância de analisar sua estrutura governamental. Para tanto, reproduzimos o método de Kubota e Maciente (2019) para estimar a tendência de automatizar as ocupações, utilizando o banco de dados de ocupações dos servidores públicos do Distrito Federal. Os resultados mostraram que empregos que exigem níveis mais baixos de escolaridade e envolvem tarefas mais rotineiras são mais propensos à automação. Por fim, com base em nossos resultados, realizamos uma análise estatística descritiva da escolaridade, idade e remuneração dos cargos públicos no Distrito Federal.Revista do Serviço Público - RSP, v. 73, n. 1, 9-31 p.Análise e Ciência de DadosGestão PúblicaISSN Impresso: 0034-9240ISSN Eletrônico: 2357-801
O PROGRAMA BRASILEIRO DE AGRICULTURA FAMILIAR: UMA REVISÃO DE SEUS PRIMEIROS DEZOITO ANOS
O presente artigo realiza uma síntese da literatura acadêmica dos últimos vinte anos relacionada ao Programa Nacional de Fortalecimento da Agricultura Familiar, o PRONAF. O referido programa foi implantado em 1996, com o principal intuito de atender as reivindicações dos atores sociais rurais ligados à agricultura familiar, os quais ressaltavam a importância e urgência da criação de linhas de crédito que suprissem suas necessidades. O trabalho está dividido em Introdução - que apresenta artigos que explicitam o contexto histórico de sua criação e as linhas de crédito com as condições dos financiamentos - em Evolução e Estruturação do Programa - contendo trabalhos que relatam as mudanças que ocorreram ao longo dos anos na sua estruturação - em Focalização e Distribuição dos Recursos - demonstrando artigos que apontam possíveis problemas como a falta de equidade na amplitude do PRONAF em cada estado brasileiro - em Desenvolvimento Econômico e Social - onde são apresentados impactos do programa que foram ressaltados por alguns autores - e por fim, a Conclusão - que retoma os pontos importantes do trabalho
Limits on the GeV Emission from Gamma-Ray Bursts
The Large Area Telescope (LAT) on board of the Fermi satellite detected
emission above 30 MeV only in a small fraction of the long gamma-ray bursts
(GRBs) detected by the Fermi Gamma-ray Burst Monitor (GBM) at 8 keV - 10 MeV.
Those bursts that were detected by the LAT were among the brightest GBM bursts.
We examine a sample of the most luminous GBM bursts with no LAT detection and
obtain upper limits on their high energy fluence. We find an average upper
limit of LAT/GBM fluence ratio of 0.13 for GeV fluence during and an
average upper limit ratio of 0.45 for GeV fluence during the first 600 seconds
after the trigger. These ratios strongly constrain various emission models and
in particular rule out SSC models for the prompt emission. In about a third of
both LAT detected and LAT non-detected bursts, we find that the extrapolation
of the MeV range Band spectrum to the GeV range is larger than the observed GeV
fluence (or its upper limit). While this excess is not highly significant for
any specific burst, the overall excess in a large fraction of the bursts
suggests a decline in the high energy spectral slope in at least some of these
bursts. Possibly an evidence for the long sought after pair creation limit.Comment: Accepted for publication in MNRA
Search for Sub-TeV Gamma Rays Coincident with BATSE Gamma Ray Bursts
Project GRAND is a 100m x 100m air shower array of proportional wire chambers
(PWCs). There are 64 stations each with eight 1.29 m^2 PWC planes arranged in
four orthogonal pairs placed vertically above one another to geometrically
measure the angles of charged secondaries. A steel plate above the bottom pair
of PWCs differentiates muons (which pass undeflected through the steel) from
non-penetrating particles. FLUKA Monte Carlo studies show that a TeV gamma ray
striking the atmosphere at normal incidence produces 0.23 muons which reach
ground level where their angles and identities are measured. Thus,
paradoxically, secondary muons are used as a signature for gamma ray primaries.
The data are examined for possible angular and time coincidences with eight
gamma ray bursts (GRBs) detected by BATSE. Seven of the GRBs were selected
because of their good acceptance by GRAND and high BATSE Fluence. The eighth
GRB was added due to its possible coincident detection by Milagrito. For each
of the eight candidate GRBs, the number of excess counts during the BATSE T90
time interval and within plus or minus five degrees of BATSE's direction was
obtained. The highest statistical significance reported in this paper (2.7
sigma) is for the event that was predicted to be the most likely to be observed
(GRB 971110).Comment: To be presented at the XXVIII International Cosmic Ray Conference,
Tsukuba, Japa
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