3,416 research outputs found
Detection of a very bright optical flare from a gamma-ray burst at redshift 6.29
In this letter we discuss the flux and the behavior of the bright optical
flare emission detected by the 25 cm TAROT robotic telescope during the prompt
high-energy emission and the early afterglow. We combine our data with
simultaneous observations performed in X-rays and we analyze the broad-band
spectrum. These observations lead us to emphasize the similarity of GRB 050904
with GRB 990123, a remarkable gamma-ray burst whose optical emission reached
9th magnitude. While GRB 990123 was, until now, considered as a unique event,
this observation suggests the existence of a population of GRBs which have very
large isotropic equivalent energies and extremely bright optical counterparts.
The luminosity of these GRBs is such that they are easily detectable through
the entire universe. Since we can detect them to very high redshift even with
small aperture telescopes like TAROT, they will constitute powerful tools for
the exploration of the high-redshift Universe and might be used to probe the
first generation of stars.Comment: 9 pages, 3 figures. Accepted in ApJ
Hands-On TAROT: Intercontinental use of the TAROT for Education and Public Outreach
The TAROT telescope has for primary goal the search for the prompt optical
counterpart of Cosmic Gamma-Ray Bursts. It is a completely autonomous 25cm
telescope installed near Nice (France), able to point any location of the sky
within 1-2 seconds. The control, scheduling, and data processing activities are
completely automated, so the instrument is completely autonomous. In addition
to its un-manned modes, we added recently the possibility to remotely control
the telescope, as a request of the "Hands-On Universe" (HOU) program for
exchange of time within automatic telescopes for the education and public
outreach. To this purpose we developed a simple control interface. A webcam was
installed to visualize the telescope. Access to the data is possible through a
web interface. The images can be processed by the HOU software, a program
specially suited for use within the classroom. We experienced these feature
during the open days of the University of California Berkeley and the Astronomy
Festival of Fleurance (France). We plan a regular use for an astronomy course
of the Museum of Tokyo, as well as for French schools. Not only does Hands-On
TAROT gives the general public an access to professional astronomy, but it is
also a more general tool to demonstrate the use of a complex automated system,
the techniques of data processing and automation. Last but not least, through
the use of telescopes located in many countries over the globe, a form of
powerful and genuine cooperation between teachers and children from various
countries is promoted, with a clear educational goal.Comment: 4 pages, Based on a demonstration presented at the ADASS X
Conference, Boston, MA, USA, October 2000, to appear in ASP Conf. Serie
Highly Non-linear Excitonic Zeeman Spin-Splitting in Composition-Engineered Artificial Atoms
Non-linear Zeeman splitting of neutral excitons is observed in composition
engineered In(x)Ga(1-x)As self-assembled quantum dots and its microscopic
origin is explained. Eight-band k.p simulations, performed using realistic dot
parameters extracted from cross-sectional scanning tunneling microscopy, reveal
that a quadratic contribution to the Zeeman energy originates from a spin
dependent mixing of heavy and light hole orbital states in the dot. The dilute
In-composition (x<0.35) and large lateral size (40-50 nm) of the quantum dots
investigated is shown to strongly enhance the non-linear excitonic Zeeman gap,
providing a blueprint to enhance such magnetic non-linearities via growth
engineering
The ultra-long GRB 111209A - II. Prompt to afterglow and afterglow properties
The "ultra-long" Gamma Ray Burst GRB 111209A at redshift z=0.677, is so far
the longest GRB ever observed, with rest frame prompt emission duration of ~4
hours. In order to explain the bursts exceptional longevity, a low metallicity
blue supergiant progenitor has been invoked. In this work, we further
investigate this peculiar burst by performing a multi-band temporal and
spectral analysis of both the prompt and the afterglow emission. We use
proprietary and publicly available data from Swift, Konus Wind, XMM-Newton,
TAROT as well as from other ground based optical and radio telescopes. We find
some peculiar properties that are possibly connected to the exceptional nature
of this burst, namely: i) an unprecedented large optical delay of 410+/-50 s is
measured between the peak epochs of a marked flare observed also in gamma-rays
after about 2 ks from the first Swift/BAT trigger; ii) if the optical and
X-ray/gamma-ray photons during the prompt emission share a common origin, as
suggested by their similar temporal behavior, a certain amount of dust in the
circumburst environment should be introduced, with rest frame visual dust
extinction of AV=0.3-1.5 mag; iii) at the end of the X-ray "steep decay phase"
and before the start of the X-ray afterglow, we detect the presence of a hard
spectral extra power law component never revealed so far. On the contrary, the
optical afterglow since the end of the prompt emission shows more common
properties, with a flux power law decay with index alpha=1.6+/-0.1 and a late
re-brightening feature at 1.1 day. We discuss our findings in the context of
several possible interpretations given so far to the complex multi-band GRB
phenomenology. We also attempt to exploit our results to further constrain the
progenitor nature properties of this exceptionally long GRB, suggesting a
binary channel formation for the proposed blue supergiant progenitor.Comment: ApJ accepted. Revised version with substantial adjustments, the main
results remain unchange
Asymmetric optical nuclear spin pumping in a single uncharged quantum dot
A highly asymmetric dynamic nuclear spin pumping is observed in a single self
assembled InGaAs quantum dot subject to resonant optical pumping of the neutral
exciton transition leading to a large maximum polarization of 54%. This dynamic
nuclear polarization is found to be much stronger following pumping of the
higher energy Zeeman state. Time-resolved measurements allow us to directly
monitor the buildup of the nuclear spin polarization in real time and to
quantitatively study the dynamics of the process. A strong dependence of the
observed dynamic nuclear polarization on the applied magnetic field is found,
with resonances in the pumping efficiency being observed for particular
magnetic fields. We develop a model that fully accounts for the observed
behaviour, where the pumping of the nuclear spin system is due to
hyperfine-mediated spin flip transitions between the states of the neutral
exciton manifold.Comment: published version; 4+ pages, 3 figures (eps
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
Strong electrically tunable exciton g-factors in an individual quantum dots due to hole orbital angular momentum quenching
Strong electrically tunable exciton g-factors are observed in individual
(Ga)InAs self-assembled quantum dots and the microscopic origin of the effect
is explained. Realistic eight band k.p simulations quantitatively account for
our observations, simultaneously reproducing the exciton transition energy, DC
Stark shift, diamagnetic shift and g-factor tunability for model dots with the
measured size and a comparatively low In-composition of x(In)~35% near the dot
apex. We show that the observed g-factor tunability is dominated by the hole,
the electron contributing only weakly. The electric field induced perturbation
of the hole wavefunction is shown to impact upon the g-factor via orbital
angular momentum quenching, the change of the In:Ga composition inside the
envelope function playing only a minor role. Our results provide design rules
for growing self-assembled quantum dots for electrical spin manipulation via
electrical g-factor modulation
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