60 research outputs found
Gamma-Ray Bursts Polarization
We review the current observational and theoretical status of the polarization measurements of Gamma-ray Bursts at all wavelengths. Gamma-Ray Bursts are thought to be produced by an ultra-relativistic jet, possibly powered by a black hole. One of the most important open point is the composition of the jet: the energy may be carried out from the central source either as kinetic energy (of baryons and/or pairs), or in electromagnetic form (Poynting flux). The polarization properties are expected to help disentangling main energy carrier. The prompt emission and afterglow polarization are also a powerful diagnostic of the jet geometry
INTEGRAL observations of the gamma-ray binary 1FGL J1018.6-5856
The Fermi-LAT collaboration has recently reported that one of their detected
sources, namely, 1FGL J1018.6-5856, is a new gamma-ray binary similar to LS
5039. This has prompted efforts to study its multi-frequency behavior. In this
report, we present the results from 5.78-Ms INTEGRAL IBIS/ISGRI observations on
the source 1FGL J1018.6-5856.
By combining all the available INTEGRAL data, a detection is made at a
significance level of 5.4 sigma in the 18-40 keV band, with an average
intensity of 0.074 counts/s . However, we find that, there is non-statistical
noise in the image that effectively reduces the significance to about 4 sigma
and a significant part of the signal appears to be located in a 0.2-wide phase
region, at phases 0.4-0.6 (where even the corrected significance amounts to 90%
of the total signal found). Given the scarcity of counts, a variability is
hinted at about 3 sigma at the hard X-rays, with an anti-correlation with the
Fermi-LAT periodicity. Should this behavior be true, it would be similar to
that found in LS 5039, and prompt observations with TeV telescopes at phases
anti-correlated with the GeV maximum.Comment: Accepted for publication in Astrophysical Journal Letters; 6 pages, 1
figur
Variable polarization measured in the prompt emission of GRB 041219A using IBIS on board INTEGRAL
Polarization measurements provide direct insight into the nature of
astrophysical processes. Unfortunately, only a few instruments are available
for this kind of measurements at gamma-ray energies, and the sources need to be
very bright. Gamma-Ray Bursts (GRBs) are ideal candidates due to their large
flux over limited time intervals, maximizing the available signal-to-noise
ratio. To date a few polarization measurements have been reported, claiming of
a high degree of polarization in the prompt emission of GRBs but with low
statistical evidence.
We used the IBIS telescope on board the INTEGRAL satellite to measure the
polarization of the prompt gamma-ray emission of the long and bright GRB
041219A in the 200-800 keV energy band. We find a variable degree of
polarization ranging from less than 4% over the first peak to 43+/-25% for the
whole second peak. Time resolved analysis of both peaks indicates a high degree
of polarization, and the null average polarization in the first peak can be
explained by the rapid variations observed in the polarization angle and
degree.
Our results are consistent with different models for the prompt emission of
GRBs at these energies, but they favor synchrotron radiation from a
relativistic outflow with a magnetic field which is coherent on an angular size
comparable with the angular size of the emitting region (~1/Gamma) . Indeed
this model has the best capabilities to maintain a high polarization level, and
to produce the observed variability.Comment: 7 pages, 3 figures, accepted for publication in the Astrophysical
Journal Letter
The Transient High Energy Sky and Early Universe Surveyor (THESEUS)
The Transient High Energy Sky and Early Universe Surveyor (THESEUS) is a mission concept under development by a large international collaboration aimed at exploiting gamma-ray bursts for investigating the early Universe. The main scientific objectives of THESEUS include: investigating the star formation rate and metallicity evolution of the ISM and IGM up to redshift 9-10, detecting the first generation (pop III) of stars, studying the sources and physics of re-ionization, detecting the faint end of galaxies luminosity function. These goals will be achieved through a unique combination of instruments allowing GRB detection and arcmin localization over a broad FOV (more than 1sr) and an energy band extending from several MeVs down to 0.3 keV with unprecedented sensitivity, as well as on-board prompt (few minutes) follow-up with a 0.6m class IR telescope with both imaging and spectroscopic capabilities. Such instrumentation will also allow THESEUS to unveil and study the population of soft and sub-energetic GRBs, and, more in general, to perform monitoring and survey of the X-ray sky with unprecedented sensitivity
Perspectives on Gamma-Ray Burst Physics and Cosmology with Next Generation Facilities
High-redshift Gamma-Ray Bursts (GRBs) beyond redshift are potentially
powerful tools to probe the distant early Universe. Their detections in large
numbers and at truly high redshifts call for the next generation of high-energy
wide-field instruments with unprecedented sensitivity at least one order of
magnitude higher than the ones currently in orbit. On the other hand, follow-up
observations of the afterglows of high-redshift GRBs and identification of
their host galaxies, which would be difficult for the currently operating
telescopes, require new, extremely large facilities of at multi-wavelengths.
This chapter describes future experiments that are expected to advance this
exciting field, both being currently built and being proposed. The legacy of
Swift will be continued by SVOM, which is equipped with a set of space-based
multi-wavelength instruments as well as and a ground segment including a wide
angle camera and two follow-up telescopes. The established Lobster-eye X-ray
focusing optics provides a promising technology for the detection of faint GRBs
at very large distances, based on which the {THESEUS}, {Einstein Probe} and
other mission concepts have been proposed. Follow-up observations and
exploration of the reionization era will be enabled by large facilities such as
{SKA} in the radio, the 30m class telescopes in the optical/near-IR, and the
space-borne {WFIRST} and {JWST} in the optical/near-IR/mid-IR. In addition, the
X-ray and -ray polarization experiment POLAR is also introduced.Comment: accepted for publication in Space Science Review; reprinted as a
chapter in a book of the Space Sciences Series of ISSI for the proceedings of
the ISSI-Beijing workshop " Gamma-Ray Bursts: a Tool to Explore the Young
Universe
Enhancing Multi-Objective Optimization through Machine Learning-Supported Multiphysics Simulation
Multiphysics simulations that involve multiple coupled physical phenomena
quickly become computationally expensive. This imposes challenges for
practitioners aiming to find optimal configurations for these problems
satisfying multiple objectives, as optimization algorithms often require
querying the simulation many times. This paper presents a methodological
framework for training, self-optimizing, and self-organizing surrogate models
to approximate and speed up Multiphysics simulations. We generate two
real-world tabular datasets, which we make publicly available, and show that
surrogate models can be trained on relatively small amounts of data to
approximate the underlying simulations accurately. We conduct extensive
experiments combining four machine learning and deep learning algorithms with
two optimization algorithms and a comprehensive evaluation strategy. Finally,
we evaluate the performance of our combined training and optimization pipeline
by verifying the generated Pareto-optimal results using the ground truth
simulations. We also employ explainable AI techniques to analyse our surrogates
and conduct a preselection strategy to determine the most relevant features in
our real-world examples. This approach lets us understand the underlying
problem and identify critical partial dependencies
HARPO: a TPC as a gamma-ray telescope and polarimeter
A gas Time Projection Chamber can be used for gamma-ray astronomy with
excellent angular-precision and sensitivity to faint sources, and for
polarimetry, through the measurement of photon conversion to pairs. We
present the expected performance in simulations and the recent development of a
demonstrator for tests in a polarized photon beam.Comment: SPIE Astronomical Telescopes + Instrumentation, Ultraviolet to gamma
ray, Montr\'eal, Canada 2014. v2: note added in proof. Copyright 2014 SPIE.
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