575 research outputs found
GRB 140206A: the most distant polarized Gamma-Ray Burst
The nature of the prompt gamma-ray emission of Gamma-Ray Bursts (GRBs) is
still far from being completely elucidated. The measure of linear polarization
is a powerful tool that can be used to put further constraints on the content
and magnetization of the GRB relativistic outflows, as well as on the radiation
processes at work.
To date only a handful of polarization measurements are available for the
prompt emission of GRBs. Here we present the analysis of the prompt emission of
GRB 140206A, obtained with INTEGRAL/IBIS, Swift/BAT, and Fermi/GBM. Using
INTEGRAL/IBIS as a Compton polarimeter we were able to constrain the linear
polarization level of the second peak of this GRB as being larger than 28% at
90% c.l.
We also present the GRB afterglow optical spectroscopy obtained at the
Telescopio Nazionale Galileo (TNG), which allowed us the measure the distance
of this GRB, z=2.739. This distance value together with the polarization
measure obtained with IBIS, allowed us to derive the deepest and most reliable
limit to date (xi <1x10-16) on the possibility of Lorentz Invariance Violation,
measured through the vacuum birefringence effect on a cosmological source.Comment: 9 pages, 5 figures, 3 tables, accepted for publication in MNRAS.
arXiv admin note: text overlap with arXiv:1303.418
Effective absorbing column density in the gamma-ray burst afterglow X-ray spectra
We investigate the scaling relation between the observed amount of absorption
in the X-ray spectra of Gamma Ray Burst (GRB) afterglows and the absorber
redshift. Through dedicated numerical simulations of an ideal instrument, we
establish that this dependence has a power law shape with index 2.4. However,
for real instruments, this value depends on their low energy cut-off, spectral
resolution and on the detector spectral response in general. We thus provide
appropriate scaling laws for specific instruments. Finally, we discuss the
possibility to measure the absorber redshift from X-ray data alone. We find
that 10^5-10^6 counts in the 0.3-10 keV band are needed to constrain the
redshift with 10% accuracy. As a test case we discuss the XMM-Newton
observation of GRB 090618 at z=0.54. We are able to recover the correct
redshift of this burst with the expected accuracy.Comment: MNRAS accepted. 6 figures. 3 table
There is a short gamma-ray burst prompt phase at the beginning of each long one
We compare the prompt intrinsic spectral properties of a sample of short
Gamma--ray Burst (GRB) with the first 0.3 seconds (rest frame) of long GRBs
observed by Fermi/GBM. We find that short GRBs and the first part of long GRBs
lie on the same E_p--E_iso correlation, that is parallel to the relation for
the time averaged spectra of long GRBs. Moreover, they are indistinguishable in
the E_p--L_iso plane. This suggests that the emission mechanism is the same for
short and for the beginning of long events, and both short and long GRBs are
very similar phenomena, occurring on different timescales. If the central
engine of a long GRB would stop after ~0.3 * (1+z) seconds the resulting event
would be spectrally indistinguishable from a short GRB.Comment: 14 pages, 6 figures, MNRAS accepte
A complete sample of bright Swift short Gamma-Ray Bursts
We present a carefully selected sample of short gamma-ray bursts (SGRBs)
observed by the Swift satellite up to June 2013. Inspired by the criteria we
used to build a similar sample of bright long GRBs (the BAT6 sample), we
selected SGRBs with favorable observing conditions for the redshift
determination on ground, ending up with a sample of 36 events, almost half of
which with a redshift measure. The redshift completeness increases up to about
70% (with an average redshift value of z = 0.85) by restricting to those events
that are bright in the 15-150 keV Swift Burst Alert Telescope energy band. Such
flux-limited sample minimizes any redshift-related selection effects, and can
provide a robust base for the study of the energetics, redshift distribution
and environment of the Swift bright population of SGRBs. For all the events of
the sample we derived the prompt and afterglow emission in both the observer
and (when possible) rest frame and tested the consistency with the correlations
valid for long GRBs. The redshift and intrinsic X-ray absorbing column density
distributions we obtain are consistent with the scenario of SGRBs originated by
the coalescence of compact objects in primordial binaries, with a possible
minor contribution (~10%-25%) of binaries formed by dynamical capture (or
experiencing large natal kicks). This sample is expected to significantly
increase with further years of Swift activity.Comment: 17 pages, 8 figures, 7 tables. Accepted for publication in MNRA
Efficient three-dimensional survey techniques and their comparison in open software in the archaeological test site of "Ninfeo Maggiore" and "Ninfeo Minore" of Formia (Latina, Italy)
In Europe and beyond, the cultural and archaeological heritage may have considerable extensions of hundreds of square metres if not kilometres. It is then necessary to study highly efficient techniques able , at the same time, to maintain centimetric accuracy. In these contexts, the SLAM technique can be an efficient solution. We tested the latter in a survey of a portion of the so-called Roman Villa of Caposele, also known as Villa Rubino in Formia, (Italy): the "Ninfeo Maggiore"and "Ninfeo Minore"(Major and Minor nymphaeum). The two structures had to be surveyed for both conservation and study purposes and to allow a virtual visit, which is particularly important since they are located inside a private property. The structure is complex, with a succession of rooms and environments in an archaeological complex extending approximately 480 metres in an east-west direction and approximately 50 metres in a south-north direction. We decided to survey both nymphaea with the "GEOSLAM Zeb Horizon", also surveying all the internal connecting rooms and corridors between them. Both nymphaea were also surveyed with a "Faro"terrestrial laser scanning, to allow comparison. To verify the validity of the SLAM on the outside, a survey was carried out using a DJI Matrix drone with laser scanning. The comparison showed very limited deviations whose statistical validation is in progress, demonstrating that the SLAM technique can advantageously be used in such vast archaeological complexes where the efficiency and completeness of the survey is more important than the millimetric accuracy.</p
GRB orphan afterglows in present and future radio transient surveys
Orphan Afterglows (OA) are slow transients produced by Gamma Ray Bursts seen
off-axis that become visible on timescales of days/years at optical/NIR and
radio frequencies, when the prompt emission at high energies (X and gamma rays)
has already ceased. Given the typically estimated jet opening angle of GRBs
theta_jet ~ 3 deg, for each burst pointing to the Earth there should be a
factor ~ 700 more GRBs pointing in other directions. Despite this, no secure
OAs have been detected so far. Through a population synthesis code we study the
emission properties of the population of OA at radio frequencies. OAs reach
their emission peak on year-timescales and they last for a comparable amount of
time. The typical peak fluxes (which depend on the observing frequency) are of
few micro Jy in the radio band with only a few OA reaching the mJy level. These
values are consistent with the upper limits on the radio flux of SN Ib/c
observed at late times. We find that the OA radio number count distribution has
a typical slope -1.7 at high fluxes and a flatter (-0.4) slope at low fluxes
with a break at a frequency-dependent flux. Our predictions of the OA rates are
consistent with the (upper) limits of recent radio surveys and archive searches
for radio transients. Future radio surveys like VAST/ASKAP at 1.4 GHz should
detect ~ 3x10^-3 OA deg^-2 yr-1, MeerKAT and EVLA at 8.4 GHz should see ~
3x10^-1 OA deg-2 yr-1. The SKA, reaching the micro Jy flux limit, could see up
to ~ 0.2-1.5 OA deg^-2 yr^-1. These rates also depend on the duration of the OA
above a certain flux limit and we discuss this effect with respect to the
survey cadence.Comment: (10 pages, 5 figures, 1 table) Accepted for publication by PAS
Toughening of complete solid solution cermets by graphite addition
(Ti0.95Ta0.05)(C0.5N0.5)-Co complete solid solution cermets (CSCs) were developed by a mechanochemical synthesis process and a pressureless sintering method. The effect of different percentages of graphite used as a sintering additive on the nature of the binder phase and the mechanical properties of the cermets was investigated. Microstructural and mechanical characterisations were carried out by X-ray diffraction, optical microscopy, scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy, Vickers hardness, indentation fracture toughness and nanoindentation. The addition of graphite modified the carbon activity during sintering, reducing the dissolution of carbonitride ceramic particles into the molten binder. The amount of Ti and Ta remaining in the binder after sintering gradually decreased as the amount of graphite added increased, which induced a change in the nature of the binder phase. When no graphite was added, the binder consisted of the brittle TixTa1-xCo2 intermetallic phase. With the increase in the amount of graphite added, the formation of more ductile phases, such as TixTa1-xCo3 and α-Co, was observed, causing a significant improvement in the toughness of the cermets.Peer reviewe
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