5,509 research outputs found
The discovery of hard X-ray emission in the persistent flux of the Rapid Burster
We report the first detection with INTEGRAL of persistent hard X-ray emission
(20 to 100 keV) from the Rapid Burster (MXB 1730-335), and describe its full
spectrum from 3 to 100 keV. The source was detected on February/March 2003
during one of its recurrent outbursts. The source was clearly detected with a
high signal to noise ratio during the single pointings and is well
distinguished from the neighboring source GX 354-0. The 3 - 100 keV X-ray
spectrum of the persistent emission is well described by a two-component model
consisting of a blackbody plus a power-law with photon index ~ 2.4. The
estimated luminosity was ~ 8.5x10^{36} erg/s in the 3 - 20 keV energy band and
\~ 1.3x10^{36} erg/s in the 20 - 100 keV energy range, for a distance of 8 kpc.Comment: 5 pages, 6 figures, 1 table. Accepted for publication in A&
INTEGRAL observation of 3EG J1736-2908
The possible identification by INTEGRAL of the EGRET source 3EG J1736-2908
with the active galactic nucleus GRS 1734-292 is discussed. The latter was
discovered in 1990 and later identified with a Seyfert 1 galaxy. At the time of
the compilation of the 3rd EGRET Catalog, it was not considered as a possible
counterpart of the source 3EG J1736-2908, which remained unidentified. A
detailed multiwavelength study of the EGRET error circle is presented, by
including archival radio, soft- and hard-X observations, suggesting that GRS
1734-292 could be a likely counterpart of 3EG J1736-2908, even though this
poses very interesting questions about the production mechanisms of gamma-rays
with energies greater than 100 MeV.Comment: 6 pages, 3 figures. Accepted for publication on A&A Main Journa
Resolving the Hard X-ray Emission of GX 5-1 with INTEGRAL
We present the study of one year of INTEGRAL data on the neutron star low
mass X-ray binary GX 5-1. Thanks to the excellent angular resolution and
sensitivity of INTEGRAL, we are able to obtain a high quality spectrum of GX
5-1 from ~5 keV to ~100 keV, for the first time without contamination from the
nearby black hole candidate GRS 1758-258 above 20 keV. During our observations,
GX 5-1 is mostly found in the horizontal and normal branch of its hardness
intensity diagram. A clear hard X-ray emission is observed above ~30 keV which
exceeds the exponential cut-off spectrum expected from lower energies. This
spectral flattening may have the same origin of the hard components observed in
other Z sources as it shares the property of being characteristic to the
horizontal branch. The hard excess is explained by introducing Compton
up-scattering of soft photons from the neutron star surface due to a thin hot
plasma expected in the boundary layer. The spectral changes of GX 5-1 downward
along the "Z" pattern in the hardness intensity diagram can be well described
in terms of monotonical decrease of the neutron star surface temperature. This
may be a consequence of the gradual expansion of the boundary layer as the mass
accretion rate increases.Comment: 10 pages, 17 figures, accepted for publication in A&
Painting the Palace of Apries I: ancient binding media and coatings of the reliefs from the Palace of Apries, Lower Egypt
This study gives an account of the organic components (binders and coatings) found in the polychromy of some fragmented architectural reliefs from the Palace of Apries in Memphis, Egypt (26th Dynasty, ca. 589-568 BCE). A column capital and five relief fragments from the collections of the Ny Carlsberg Glyptotek in Copenhagen were chosen for examination, selected because of their well-preserved polychromy. Samples from the fragments were first investigated using Fourier transform infrared (FTIR) spectroscopy to screen for the presence of organic materials and to identify the chemical family to which these materials belong (proteinaceous, polysaccharides or lipid). Only the samples showing the potential presence of organic binder residues were further investigated using gas chromatography with mass spectrometry detection (GC-MS) targeting the analysis towards the detection and identification of compounds belonging to the chemical families identified by FTIR. The detection of polysaccharides in the paint layers on the capital and on two of the fragments indicates the use of plant gums as binding media. The interpretation of the sugar profiles was not straightforward so botanical classification was only possible for one fragment where the results of analysis seem to point to gum arabic. The sample from the same fragment was found to contain animal glue and a second protein material (possibly egg). While the presence of animal glue is probably ascribable to the binder used for the ground layer, the second protein indicates that either the paint layer was bound in a mixture of different binding materials or that the paint layer, bound in a plant gum, was then coated with a proteinaceous material. The surface of two of the investigated samples was partially covered by translucent waxy materials that were identified as a synthetic wax (applied during old conservation treatments) and as beeswax, respectively. It is possible that the beeswax is of ancient origin, selectively applied on yellow areas in order to create a certain glossiness or highlight specific elements
Spectral evolution of bright NS LMXBs with INTEGRAL: an application of the thermal plus bulk Comptonization model
The aim of this work is to investigate in a physical and quantitative way the
spectral evolution of bright Neutron Star Low-Mass X-ray Binaries (NS LMXBs),
with special regard to the transient hard X-ray tails. We analyzed INTEGRAL
data for five sources (GX 5-1, GX 349+2, GX 13+1, GX 3+1, GX 9+1) and built
broad-band X-ray spectra from JEM-X1 and IBIS/ISGRI data. For each source,
X-ray spectra from different states were fitted with the recently proposed
model compTB. The spectra have been fit with a two-compTB model. In all cases
the first compTB describes the dominant part of the spectrum that we interpret
as thermal Comptonization of soft seed photons (< 1 keV), likely from the
accretion disk, by a 3-5 keV corona. In all cases, this component does not
evolve much in terms of Comptonization efficiency, with the system converging
to thermal equilibrium for increasing accretion rate. The second compTB varies
more dramatically spanning from bulk plus thermal Comptonization of blackbody
seed photons to the blackbody emission alone. These seed photons (R < 12 km,
kT_s > 1 keV), likely from the neutron star and the innermost part of the
system, the Transition Layer, are Comptonized by matter in a converging flow.
The presence and nature of this second compTB component (be it a pure blackbody
or Comptonized) are related to the inner local accretion rate which can
influence the transient behaviour of the hard tail: high values of accretion
rates correspond to an efficient Bulk Comptonization process (bulk parameter
delta > 0) while even higher values of accretion rates suppress the
Comptonization, resulting in simple blackbody emission (delta=0).Comment: 12 pages, 10 figures, accepted for publication in A&
GRB 021219: the first Gamma-Ray Burst localized in real time with IBAS
On December 19, 2002, during the Performance and Verification Phase of
INTEGRAL, a Gamma-Ray Burst (GRB) has been detected and localized in real time
with the INTEGRAL Burst Alert System (IBAS). Here we present the results
obtained with the IBIS and SPI instruments. The burst had a time profile with a
single peak lasting about 6 s. The peak spectrum can be described by a single
power law with photon index =1.60.1 and flux 3.7 photons
cm s (20 - 200 keV). The fluence in the same energy range is
9 erg cm. Time resolved spectroscopy performed with
IBIS/ISGRI shows a clear hard to soft evolution of the spectrum.Comment: 4 pages, 3 figures, latex, accepted for publication in A&A INTEGRAL
special issu
The hard X-ray emission of X Per
We present an analysis of the spectral properties of the peculiar X-ray
pulsar X Per based on INTEGRAL observations. We show that the source exhibits
an unusually hard spectrum and is confidently detected by ISGRI up to more than
100 keV. We find that two distinct components may be identified in the
broadband 4-200 keV spectrum of the source. We interpret these components as
the result of thermal and bulk Comptonization in the vicinity of the neutron
star and describe them with several semi-phenomenological models. The
previously reported absorption feature at ~30 keV is not required in the
proposed scenario and therefore its physical interpretation must be taken with
caution. We also investigated the timing properties of the source in the
framework of existing torque theory, concluding that the observed phenomenology
can be consistently explained if the magnetic field of the neutron star is
~10^14 G.Comment: Published as a letter in A&A; 4 pages, 2 figure
INTEGRAL high energy monitoring of the X-ray burster KS 1741-293
KS 1741-293, discovered in 1989 by the X-ray camera TTM in the Kvant module
of the Mir space station and identified as an X-ray burster, has not been
detected in the hard X band until the advent of the INTEGRAL observatory.
Moreover this source has been recently object of scientific discussion, being
also associated to a nearby extended radio source that in principle could be
the supernova remnant produced by the accretion induced collapse in the binary
system. Our long term monitoring with INTEGRAL, covering the period from
February 2003 to May 2005, confirms that KS 1741-293 is transient in soft and
hard X band. When the source is active, from a simultaneous JEM-X and IBIS data
analysis, we provide a wide band spectrum from 5 to 100 keV, that can be fit by
a two component model, a multiple blackbody for the soft emission and a
Comptonized or a cut-off power law model for the hard component. Finally, by
the detection of two X-ray bursters with JEM-X, we confirm the bursting nature
of KS 1741-293, including this source in the class of the hard tailed X-ray
bursters.Comment: 7 pages, accepted for publication on MNRA
First INTEGRAL Observations of Eight Persistent Neutron Star Low Mass X-ray Binaries
Early results from the INTEGRAL Core Program, for a sample of eight
persistently bright neutron star low mass X-ray binaries in the energy range
from 5 keV to 200 keV are presented. It is shown that INTEGRAL efficiently
detects sources and that spectra may be obtained up to several hundreds of keV
by combining data from three of the four INTEGRAL instruments: JEM-X, IBIS and
SPI. For the source GX 17+2 it is shown that the spectrum extends well above
100 keV with a flattening of the spectrum above 30 keV. This might suggest a
non-thermal comptonisation emission, but uncertainties in the current data
reduction and background determination do not allow firm conclusions to be
drawn.Comment: 5 pages, 6 figures, accepted for publication in Astronomy &
Astrophysic
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