1,570 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
The first giant flare from SGR 1806-20: observations with the INTEGRAL SPI Anti-Coincidence Shield
A giant flare from the Soft Gamma-ray Repeater SGR 1806-20 has been detected
by several satellites on 2004 December 27. This tremendous outburst, the first
one observed from this source, was a hundred times more powerful than the two
previous giant flares from SGR 0525-66 and SGR 1900+14. We report the results
obtained for this event with the Anticoincidence Shield of the SPI spectrometer
on board the INTEGRAL satellite, which provides a high-statistics light curve
at E>~80 keV. The flare started with a very strong pulse, which saturated the
detector for ~0.7 s, and whose backscattered radiation from the Moon was
detected 2.8 s later. This was followed by a ~400 s long tail modulated at the
neutron star rotation period of 7.56 s. The tail fluence corresponds to an
energy in photons above 3 keV of 1.6x10^44 (d/15 kpc)^2 erg. This is of the
same order of the energy emitted in the pulsating tails of the two giant flares
seen from other soft repeaters, despite the hundredfold larger overall emitted
energy of the SGR 1806-20 giant flare. Long lasting (~1 hour) hard X-ray
emission, decaying in time as t^-0.85, and likely associated to the SGR 1806-20
giant flare afterglow has also been detected.Comment: revised version - Accepted for publication on The Astrophysical
Journal Letter
The X-ray spectrum of the bursting atoll source 4U~1728-34 observed with INTEGRAL
We present for the first time a study of the 3-200 keV broad band spectra of
the bursting atoll source 4U 1728-34 (GX 354-0) along its hardness intensity
diagram. The analysis was done using the INTEGRAL public and Galactic Center
deep exposure data ranging from February 2003 to October 2004. The spectra are
well described by a thermal Comptonization model with an electron temperature
from 35 keV to 3 keV and Thomson optical depth, tau_T, from 0.5 to 5 in a slab
geometry. The source undergoes a transition from an intermediate/hard to a soft
state where the source luminosity increases from 2 to 12% of Eddington. We have
also detected 36 type I X-ray bursts two of which show photospheric radius
expansion. The energetic bursts with photospheric radius expansion occurred at
an inferred low mass accretion rate per unit area of \dot m ~ 1.7x10E3 g/cm2/s,
while the others at a higher one between 2.4x10E3 - 9.4x10E3 g/cm2/s. For
4U1728-34 the bursts' total fluence, and the bursts' peak flux are
anti-correlated with the mass accretion rate. The type I X-ray bursts involve
pure helium burning either during the hard state, or during the soft state of
the source.Comment: 11 pages, 7 figures, and 2 tables. Accepted for publication in A&
In-flight calibration of the INTEGRAL/IBIS mask
Since the release of the INTEGRAL Offline Scientific Analysis (OSA) software
version 9.0, the ghost busters module has been introduced in the INTEGRAL/IBIS
imaging procedure, leading to an improvement of the sensitivity around bright
sources up to a factor of 7. This module excludes in the deconvolution process
the IBIS/ISGRI detector pixels corresponding to the projection of a bright
source through mask elements affected by some defects. These defects are most
likely associated with screws and glue fixing the IBIS mask to its support.
Following these major improvements introduced in OSA 9, a second order
correction is still required to further remove the residual noise, now at a
level of 0.2-1% of the brightest source in the field of view. In order to
improve our knowledge of the IBIS mask transparency, a calibration campaign has
been carried out during 2010-2012. We present here the analysis of these data,
together with archival observations of the Crab and Cyg X-1, that allowed us to
build a composite image of the mask defects and to investigate the origin of
the residual noise in the IBIS/ISGRI images. Thanks to this study, we were able
to point out a simple modification of the ISGRI analysis software that allows
to significantly improve the quality of the images in which bright sources are
detected at the edge of the field of view. Moreover, a refinement of the area
excluded by the ghost busters module is considered, and preliminary results
show improvements to be further tested. Finally, this study indicates further
directions to be investigated for improving the ISGRI sensitivity, such as
taking into account the thickness of the screws in the mask model or studying
the possible discrepancy between the modeled and actual mask element bridges.Comment: accepted for publication in the proceedings of "An INTEGRAL view of
the high-energy sky (the first 10 years)" 9th INTEGRAL Workshop, October
15-19, 2012, Paris, France, in Proceedings of Science (INTEGRAL 2012), Eds.
A. Goldwurm, F. Lebrun and C. Winkler,
(http://pos.sissa.it/cgi-bin/reader/conf.cgi?confid=176), id 154; 6 pages, 4
figures, see the PoS website for the full resolution versio
The discovery, monitoring and environment of SGR J1935+2154
We report on the discovery of a new member of the magnetar class, SGR
J1935+2154, and on its timing and spectral properties measured by an extensive
observational campaign carried out between July 2014 and March 2015 with
Chandra and XMM-Newton (11 pointings). We discovered the spin period of SGR
J1935+2154 through the detection of coherent pulsations at a period of about
3.24s. The magnetar is slowing-down at a rate of 1.43(1)x10^{-11} s/s and with
a decreasing trend due to a negative second period derivative of
-3.5(7)x10^{-19} s/s^2. This implies a surface dipolar magnetic field strength
of about 2.2x10^{14} G, a characteristic age of about 3.6kyr and, a spin-down
luminosity L_{sd} of about 1.7x10^{34} erg/s. The source spectrum is well
modelled by a blackbody with temperature of about 500eV plus a power-law
component with photon index of about 2. The source showed a moderate long-term
variability, with a flux decay of about 25\% during the first four months since
its discovery, and a re-brightening of the same amount during the second four
months. The X-ray data were also used to study the source environment. In
particular, we discovered a diffuse emission extending on spatial scales from
about 1" up to at least 1' around SGR J1935+2154 both in Chandra and XMM-Newton
data. This component is constant in flux (at least within uncertainties) and
its spectrum is well modelled by a power-law spectrum steeper than that of the
pulsar. Though a scattering halo origin seems to be more probable we cannot
exclude that part, or all, of the diffuse emission is due to a pulsar wind
nebula.Comment: To appear in MNRAS; 10 pages, 3 color figures, 4 table
IGR J08408--4503: a new recurrent Supergiant Fast X-ray Transient
The supergiant fast X-ray transient IGR J08408-4503 was discovered by
INTEGRAL on May 15, 2006, during a bright flare. The source shows sporadic
recurrent short bright flares, reaching a peak luminosity of 10^36 erg s^-1
within less than one hour. The companion star is HD 74194, an Ob5Ib(f)
supergiant star located at 3 kpc in the Vela region. We report the light curves
and broad-band spectra (0.1-200 keV) of all the three flares of IGR J08408-4503
detected up to now based on INTEGRAL and Swift data. The flare spectra are well
described by a power-law model with a high energy cut-off at ~15 keV. The
absorption column density during the flares was found to be ~10^21 cm^-2,
indicating a very low matter density around the compact object. Using the
supergiant donor star parameters, the wind accretion conditions imply an
orbital period of the order of one year, a spin period of the order of hours
and a magnetic field of the order of 10^13 G.Comment: 5 pages, 2 figures, accepted for publication in Astrophysical Journal
Letter
Models for Modules
We recall the structure of the indecomposable sl(2) modules in the
Bernstein-Gelfand-Gelfand category O. We show that all these modules can arise
as quantized phase spaces of physical models. In particular, we demonstrate in
a path integral discretization how a redefined action of the sl(2) algebra over
the complex numbers can glue finite dimensional and infinite dimensional
highest weight representations into indecomposable wholes. Furthermore, we
discuss how projective cover representations arise in the tensor product of
finite dimensional and Verma modules and give explicit tensor product
decomposition rules. The tensor product spaces can be realized in terms of
product path integrals. Finally, we discuss relations of our results to brane
quantization and cohomological calculations in string theory.Comment: 18 pages, 6 figure
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