326 research outputs found
Continuous optical monitoring during the prompt emission of GRB 060111B
We present the time-resolved optical emission of GRB 060111B during its
prompt phase, measured with the TAROT robotic observatory. This is the first
time that the optical emission from a gamma-ray burst has been continuously
monitored with a temporal resolution of a few seconds during the prompt
gamma-ray phase. The temporal evolution of the prompt optical emission at the
level of several seconds is used to provide a clue to the origin of this
emission. The optical emission was found to decay steadily from our first
measure, 28s after the trigger, in contrast to the gamma-ray emission, which
exhibits strong variability at the same time. This behaviour strongly suggests
that the optical emission is due to the reverse shock
GRB 130427A Afterglow: A Test for GRB Models
Gamma-ray Burst 130427A had the largest fluence for almost 30 years. With an isotropic energy output of 8.5Ă1053 erg and redshift of 0.34, it combined a very high energy release with a relative proximity to Earth in an unprecedented fashion. Sensitive X-ray facilities such as {\it XMM-Newton} and {\it Chandra} detected the afterglow of this event for a record-breaking baseline of 90 Ms. We show the X-ray light curve of GRB 130427A of this event over such an interval. The light curve shows an unbroken power law decay with a slope of α=1.31 over more than three decades in time. In this presentation, we investigate the consequences of this result for the scenarios proposed to interpret GRB 130427A and the implications in the context of the forward shock model (jet opening angle, energetics, surrounding medium). We also remark the chance of extending GRB afterglow observations for several hundreds of Ms with {\it Athena}
Limits on the early afterglow phase of gamma-ray burst sources from TAROT-1
The T\'elescope \`a Action Rapide pour les Objets Transitoires (TAROT-1) has
as prime objective the observation of the prompt and delayed emission of cosmic
gamma-ray bursts (GRBs). We have performed a search for optical emission from 6
GRBs detected by BATSE. The positioning error circle was fully covered within
typically thirty minutes after the trigger. No detection of the early afterglow
phase was made, and magnitude limits in the range of were estimated using 20s exposures. These limits are compared to
optical afterglow data obtained in later phases and the results are interpreted
in terms of source distances. They correspond to a median redshift of z = 0.5.
With HETE-2 and the planned instrument upgrade, TAROT-1 will be able to detect
the early optical emission of GRBs up to a redshift of the order of 5.Comment: 7 pages, accepted in Astronomy and Astrophysic
Irrigation and energy: Issues and challenges
Waterâefficient agriculture has implied a large increase in energy consumption for irrigation in recent decades. In many irrigation systems, energy costs are now threatening their sustainability. However, new opportunities have arisen for the use of renewable energies in the irrigation sector. These are some of the aspects of the multifaceted multipleâactor 'waterâfoodâenergy' nexus. Technical, economic and environmental issues are linked in many ways, involving farmers, water users' associations, energy suppliers, engineers and other stakeholders. The ICID session 'Irrigation and energy' triggered discussions on these multiple dimensions. This paper presents a synthesis of the presentations, discussions and conclusions. Four main questions are addressed: How do irrigation productivity and sustainability of water resources exploitation change when farmers have access to energy? What do we know about energy efficiency in irrigation systems, at farm and collective network levels? How can this efficiency be optimized by using advanced technologies, modelling tools, improved management? Is energy production an opportunity for irrigation systems? These questions have been posed based on multiple case studies from different parts of the world. The BRL network, in southern France, illustrates advanced strategies and opportunities to reduce energy consumption and develop energy production at a network level. General conclusions are drawn from this synthesis, illustrating tradeâoffs and synergies that can be identified in the irrigation sector at different scales, while opportunities for future research are proposed
Swift multi-wavelength observations of the bright flaring burst GRB051117A
We report on the temporal and spectral characteristics of the early X-ray
emission from the Gamma Ray Burst 051117A as observed by Swift. The superb
quality of the early X-ray light-curve and spectra of this source, one of the
brightest seen by the X-ray Telescope at such early times, allows an
unprecedented look at the spectral and temporal evolution of the prompt and
early afterglow emission for this GRB and allows us to place stringent limits
on the detection of lines. The X-ray light-curve at early times is
characteristic of a shot-noise process, with individual shots well-modelled by
a fast-rise and exponential decay spanning a broad range in rise-times and
decay rates. A temporal spectral analysis of the early light-curve shows that
the photon index and source intensity are highly correlated with the spectrum
being significantly harder when brighter, consistent with the movement of the
peak of the Band function to lower energies following individual flares. The
high quality spectrum obtained from the first orbit of WT mode data, enables us
to place a 3 sigma upper limit on the strength of any emission line features of
EW < 15 eV, assuming a narrow emission-line of 100 eV at the peak of the
effective area (abridged).Comment: Accepted 15/3/2007 - To appear in A&
A complete sample of bright Swift Gamma-Ray Bursts: X-ray afterglow luminosity and its correlation with the prompt emission
We investigate wheter there is any correlation between the X-ray afterglow
luminosity and the prompt emission properties of a carefully selected
sub-sample of bright Swift long Gamma-Ray Bursts (GRBs) nearly complete in
redshift (~90%). Being free of selection effects (except flux limit), this
sample provides the possibility to compare the rest frame physical properties
of GRB prompt and afterglow emission in an unbiased way. The afterglow X-ray
luminosities are computed at four different rest frame times (5 min, 1 hr, 11
hr and 24 hr after trigger) and compared with the prompt emission isotropic
energy E_iso, the isotropic peak luminosity L_iso and the rest frame peak
energy E_peak. We find that the rest frame afterglow X-ray luminosity do
correlate with these prompt emission quantities, but the significance of each
correlation decreases over time. This result is in agreement with the idea that
the GRB X-ray light curve can be described as the result of a combination of
different components whose relative contribution and weight change with time,
with the prompt and afterglow emission dominating at early and late time,
respectively. In particular, we found evidence that the plateau and the shallow
decay phase often observed in GRB X-ray light curves are powered by activity
from the central engine. The existence of the L_X-E_iso correlation at late
times (t_rf > 11 hr) suggests a similar radiative efficiency among different
bursts with on average about 6% of the total kinetic energy powering the prompt
emission.Comment: 8 pages, 4 figures, 3 tables. Accepted for publication in MNRA
Challenging GRB models through the broadband dataset of GRB060908
Context: Multiwavelength observations of gamma-ray burst prompt and afterglow
emission are a key tool to disentangle the various possible emission processes
and scenarios proposed to interpret the complex gamma-ray burst phenomenology.
Aims: We collected a large dataset on GRB060908 in order to carry out a
comprehensive analysis of the prompt emission as well as the early and late
afterglow. Methods: Data from Swift-BAT, -XRT and -UVOT together with data from
a number of different ground-based optical/NIR and millimeter telescopes
allowed us to follow the afterglow evolution from about a minute from the
high-energy event down to the host galaxy limit. We discuss the physical
parameters required to model these emissions. Results: The prompt emission of
GRB060908 was characterized by two main periods of activity, spaced by a few
seconds of low intensity, with a tight correlation between activity and
spectral hardness. Observations of the afterglow began less than one minute
after the high-energy event, when it was already in a decaying phase, and it
was characterized by a rather flat optical/NIR spectrum which can be
interpreted as due to a hard energy-distribution of the emitting electrons. On
the other hand, the X-ray spectrum of the afterglow could be fit by a rather
soft electron distribution. Conclusions: GRB060908 is a good example of a
gamma-ray burst with a rich multi-wavelength set of observations. The
availability of this dataset, built thanks to the joint efforts of many
different teams, allowed us to carry out stringent tests for various
interpretative scenarios showing that a satisfactorily modeling of this event
is challenging. In the future, similar efforts will enable us to obtain
optical/NIR coverage comparable in quality and quantity to the X-ray data for
more events, therefore opening new avenues to progress gamma-ray burst
research.Comment: A&A, in press. 11 pages, 5 figure
ORIGIN: Metal Creation and Evolution from the Cosmic Dawn
ORIGIN is a proposal for the M3 mission call of ESA aimed at the study of metal creation from the epoch of cosmic dawn. Using high-spectral resolution in the soft X-ray band, ORIGIN will be able to identify the physical conditions of all abundant elements between C and Ni to red-shifts of z=10, and beyond. The mission will answer questions such as: When were the first metals created? How does the cosmic metal content evolve? Where do most of the metals reside in the Universe? What is the role of metals in structure formation and evolution? To reach out to the early Universe ORIGIN will use Gamma-Ray Bursts (GRBs) to study their local environments in their host galaxies. This requires the capability to slew the satellite in less than a minute to the GRB location. By studying the chemical composition and properties of clusters of galaxies we can extend the range of exploration to lower redshifts (z approx. 0.2). For this task we need a high-resolution spectral imaging instrument with a large field of view. Using the same instrument, we can also study the so far only partially detected baryons in the Warm-Hot Intergalactic Medium (WHIM). The less dense part of the WHIM will be studied using absorption lines at low redshift in the spectra for GRBs. The ORIGIN mission includes a Transient Event Detector (coded mask with a sensitivity of 0.4 photon/sq cm/s in 10 s in the 5-150 keV band) to identify and localize 2000 GRBs over a five year mission, of which approx.65 GRBs have a redshift >7. The Cryogenic Imaging Spectrometer, with a spectral resolution of 2.5 eV, a field of view of 30 arcmin and large effective area below 1 keV has the sensitivity to study clusters up to a significant fraction of the virial radius and to map the denser parts of the WHIM (factor 30 higher than achievable with current instruments). The payload is complemented by a Burst InfraRed Telescope to enable onboard red-shift determination of GRBs (hence securing proper follow up of high-z bursts) and also probes the mildly ionized state of the gas. Fast repointing is achieved by a dedicated Controlled Momentum Gyro and a low background is achieved by the selected low Earth orbit
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