5,661 research outputs found
High Energy Emission from the Prompt Gamma-Ray Burst
We study the synchrotron and synchrotron self-Compton (SSC) emission from
internal shocks that are responsible for the prompt gamma-ray emission in GRBs,
and consider the relation between these two components, taking into account the
high energy (HE) cutoff due to pair production and Thomson scattering. We find
that in order for the peak energy of the synchrotron to be E_p\sim 300 keV with
a variability time t_v>1 ms, a Lorentz factor \Gamma<350 is needed, implying no
HE emission above \sim 30 MeV and the synchrotron component would dominate at
all energies. If we want both E_p\sim 300 keV and prompt HE emission up to 2
GeV, as detected by EGRET for GRB 940217, we need \Gamma\sim 600 and t_v\sim
0.1 ms, which might be resolved by super AGILE. If such prompt HE emission is
common in GRBs, as may be tested by GLAST, then for t_v\gtrsim 1 ms we need
\Gamma\gtrsim 350, which implies E_p\lesssim 100 keV. Therefore if X-ray
flashes are GRBs with high values of t_v and \Gamma, they should produce
\gtrsim 1 GeV emission. For an electron power law index p>2, the SSC component
dominates the emission above 100 MeV. Future observations by GLAST may help
determine the value of p and whether the HE emission is consistent with a
single power law (one component--the synchrotron, dominates) or has a break
where the \nuF_\nu slope turns from negative to positive, implying that the SSC
component becomes dominant above \sim 100 MeV. The HE emission is expected to
show similar variability and time structure to that of the soft gamma-ray
emission. Finally, we find that in order to see delayed HE emission from the
prompt GRB due to pair production with the cosmic IR background, extremely
small intergalactic magnetic fields (\lessim 10^{-22} G) are required.Comment: 11 pages, 1 figur
Estimates of Genetic and Phenotypic Trends of Growth Traits in Bali Cattle
The aim of this study was to estimate genetic and phenotypic trends for growth traits including birth (BW), weaning (WW) and yearling weight (YW) in Bali cattle. The number of cattle used to determine growth traits of BW, WW, and YW were 235, 215, and 178 heads, respectively. Estimation of breeding value, phenotypic and genetic correlation were calculated by Restricted Maximum Likelihood and General Linier Model (GLM) procedures, respectively. Genetic trends analysis was performed using the regression mean breeding values on birth year. Phenotypic and genetic correlation among BW and WW were 0.10 and 0.08 respectively and 0.90 and 0.70 for WW and YW respectively. The phenotypic trends for traits of birth and weaning weight were constant, whereas yearling weight was fluctuating from 2000 to 2008. Likewise, in the case of genetic trends, the birth and weaning weight were constant from 2000 to 2008 except for WW in 2005, whereas the genetic trends for yearling weight showed a fluctuation of wide range. According to the breeding value estimated for all traits, the best was the sire No. 0565, whose breeding value for BW, WW and YW were +0.07, +2.79, and +10.25 kg, respectively higher than the mean value of the population. The genetic trends showed that there have been a significant and positive genetic improvement in all growth traits and indicate that selection would be effective. Genetic correlation between WW and YW was high (0.70) which indicates that the selection on weaning weight might also increase yearling weight in Bali cattle
Broad-band Modeling of GRB Afterglows
Observations of GRB afterglows ranging from radio to X-ray frequencies
generate large data sets. Careful analysis of these broad-band data can give us
insight into the nature of the GRB progenitor population by yielding such
information like the total energy of the burst, the geometry of the fireball
and the type of environment into which the GRB explodes. We illustrate, by
example, how global, self-consistent fits are a robust approach for
characterizing the afterglow emission. This approach allows a relatively simple
comparison of different models and a way to determine the strengths and
weaknesses of these models, since all are treated self-consistently. Here we
quantify the main differences between the broad-band, self-consistent approach
and the traditional approach, using GRB000301C and GRB970508 as test cases.Comment: Appears in "Gamma-Ray Bursts in the Afterglow Era" proceedings of the
Roma 2000 GRB Workshop; 3 pages; 2 figure
Power Density Spectra of Gamma-Ray Bursts in the Internal Shock Model
We simulate Gamma-Ray Bursts arising from internal shocks in relativistic
winds, calculate their power density spectrum (PDS), and identify the factors
to which the PDS is most sensitive: the wind ejection features, which determine
the wind dynamics and its optical thickness, and the energy release parameters,
which give the pulse 50-300 keV radiative efficiency. For certain combinations
of ejection features and wind parameters the resulting PDS exhibits the
features observed in real bursts. We found that the upper limit on the
efficiency of conversion of wind kinetic energy into 50-300 keV photons is
1%. Winds with a modulated Lorentz factor distribution of the ejecta
yield PDSs in accord with current observations and have efficiencies closer to
, while winds with a random, uniform Lorentz factor ejection must be
optically thick to the short duration pulses to produce correct PDSs, and have
an overall efficiency around .Comment: 6 pages, 4 figures, Latex, submitted to The Astrophysical Journal
(05/04/99
On The Synchrotron Self-Compton Emission from Relativistic Shocks and Its Implications for Gamma-Ray Burst Afterglows
We consider the effects of inverse Compton scattering of synchrotron photons
from relativistic electrons in GRB afterglows. We compute the spectrum of the
inverse Compton emission and find that it can dominate the total cooling rate
of the afterglow for several months or even years after the initial explosion.
We demonstrate that the presence of strong inverse Compton cooling can be
deduced from the effect it has on the time-evolution of the cooling break in
the synchrotron spectral component, and therefore on the optical and X-ray
afterglow lightcurves. We then show how the physical interpretation of the
observed characteristics of the synchrotron spectrum must be modified to take
into consideration this extra source of cooling, and give a revised
prescription for computing physical parameters characterizing the expanding
shock wave from the observed quantities. We find that for a given set of
observables (synchrotron break frequencies and fluxes) there is either no
consistent physical interpretation or two of them. Finally we discuss the
prospects of directly detecting the inverse Compton emission with Chandra. We
argue that such a detection is possible for GRBs exploding in a reasonably
dense (n>1 cm^-3) medium.Comment: 21 pages, ApJ submitte
Educational Leadership in Haiti: A Case Study of Innovative and Exemplary Leadership in a Fragile State
In this study, we consider three school leaders in Haiti who provide examples of innovative and exemplary leadership practices in the midst of challenging circumstances. Using a framework of innovative (Moolenaar, Daly, & Sleeger, 2010; Rogers, 2003) and exemplary leadership practices (Kouzes & Posner, 2006), we examine three themes that emerged from interviews with the three participants, observations of their work in the field, and interviews with other educational stakeholders in their communities. We raise considerations for leadership practices that include: The importance of social and professional networks, barriers and opportunities to innovative practice, and collaborations involving community, regional, national, and international partners. The paper provides suggestions for further exploration in examining educational leadership in fragile states such as Haiti
A Compact Fireball Model of Gamma Ray Bursts
It is proposed that the gamma ray burst photons near the peak of the spectrum
at several hundred KeV are produced on very compact scales, where photon
production is limited by blackbody effects and/or the requirement of energetic
quanta () for efficient further production. The fast variation of
order milliseconds in the time profile is then a natural expectation, given the
other observed GRB parameters. Analytic calculations are presented to show that
the escape of non-thermal, energetic gamma rays can emerge within a second of
the thermal photons from a gammasphere of below cm. The minimum
asymptotic bulk Lorentz factor in this model is found to be of order several
hundred if the photosphere is of order cm and greater for
larger or smaller photospheric radii. It is suggested that prompt UHE gamma
rays might provide a new constraint on the asymptotic Lorentz factor of the
outflow.Comment: To appear in ApJ, revisions requested by the refere
GRB990123, The Optical Flash and The Fireball Model
We compare the ongoing observations of the remarkable burst GRB990123, the
mother of all bursts, with the predictions of the afterglow theory. We show
that the observations agree with the recent prediction that a reverse shock
propagating into the ejecta would produce a very strong prompt optical flash.
This reverse shock has also produced the 8.46GHz radio signal, observed after
one day. The forward shock, which propagates into the ISM is the origin of the
classical afterglow. It has produced the prompt X-ray signal as well as the
late optical and IR emission. It would most likely produce a radio emission
within the next few weeks. The observations suggest that the initial Lorentz
factor of the ejecta was . Within factors of order unity, this crude
model explains all current observations of GRB990123.Comment: 14 pages including 2 figure
Constraints on Off-Axis X-Ray Emission from Beamed GRBs
We calculate the prompt x-ray emission as a function of viewing angle for
beamed Gamma-Ray Burst (GRB) sources. Prompt x-rays are inevitable due to the
less highly blueshifted photons emitted at angles greater than 1/gamma relative
to the beam symmetry axis, where gamma is the expansion Lorentz factor. The
observed flux depends on the combinations (gamma Delta theta) and (gamma
theta_v), where (Delta theta) is the beaming angle and theta_v is the viewing
angle. We use the observed source counts of gamma-ray-selected GRBs to predict
the minimum detection rate of prompt x-ray bursts as a function of limiting
sensitivity. We compare our predictions with the results from the Ariel V
catalog of fast x-ray transients, and find that Ariel's sensitivity is not
great enough to place significant constraints on gamma and (Delta theta). We
estimate that a detector with fluence limit ~10^{-7} erg/cm^2 in the 2-10 keV
channel will be necessary to distinguish between geometries. Because the x-ray
emission is simultaneous with the GRB emission, our predicted constraints do
not involve any model assumptions about the emission physics but simply follow
from special-relativistic considerations.Comment: Submitted to Ap
Android Educational Game: Introduction to Basic Logic for Children
Introduction to Basic Logic aims to develop children\u27s thinking abilities about numbers and quantities to teach activities that are in accordance with the development of their thinking power. Learning in children requires an educational media game facility, one of which is the Educational Game. This educational type game aims to provoke children\u27s interest in learning the subject matter while playing the game. Mobile games can be an alternative in children\u27s learning. Basically children prefer to play rather than learn. This is natural, because child psychology is playing. Based on these problems an educational game application is made for the introduction of basic logic in Android-based children, so that it can produce alternative learning for children. This educational game is intended for children aged 6-7 years because children aged 6-7 years have begun to understand the concept of numbers and develop sensitivity in solving a problem. And trials are carried out using a questionnair
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