388 research outputs found
The broad band spectral properties of binary X-ray pulsars
The X-ray telescopes on board BeppoSAX are an optimal set of instruments to
observe bright galactic binary pulsars. These sources emit very hard and quite
complex X-ray spectra that can be accurately measured with BeppoSAX between 0.1
and 200 keV. A prototype of this complexity, the source Her X-1, shows at least
seven different components in its spectrum. A broad band measure is therefore
of paramount importance to have a thorough insight into the physics of the
emitting region. Moreover the detection of cyclotron features, when present,
allows a direct and highly significant measure of the magnetic field intensity
in the emission region. In this paper we briefly report the results obtained
with BeppoSAX on this class of sources, with emphasis on the detection and on
the measured properties of the cyclotron lines.Comment: 10 Latex pages, 4 figures, uses psfig.sty. Accepted for publication
in Advances in Space Research, in Proceedings of 32nd Scientific Assembly of
COSPAR - Symposium E1.1: "Broad-Band X-ray Spectroscopy of Cosmic Sources
Broadband observations of the X-ray burster 4U 1705-44 with BeppoSAX
4U 1705-44 is one of the most-studied type I X-ray burster and Atoll sources.
This source represents a perfect candidate to test different models proposed to
self-consistently track the physical changes occurring between different
spectral states because it shows clear spectral state transitions. The
broadband coverage, the sensitivity and energy resolution of the BeppoSAX
satellite offers the opportunity to disentangle the components that form the
total X-ray spectrum and to study their changes according to the spectral
state. Using two BeppoSAX observations carried out in August and October 2000,
respectively, for a total effective exposure time of about 100 ks, we study the
spectral evolution of the source from a soft to hard state. Energy spectra are
selected according to the source position in the color-color diagram (CCD)
Results. We succeeded in modeling the spectra of the source using a physical
self-consistent scenario for both the island and banana branches (the double
Comptonization scenario). The components observed are the soft Comptonization
and hard Comptonization, the blackbody, and a reflection component with a broad
iron line. When the source moves from the banana state to the island state, the
parameters of the two Comptonization components change significantly and the
blackbody component becomes too weak to be detected. We interpret the soft
Comptonization component as emission from the hot plasma surrounding the
neutron star, hard Comptonization as emission from the disk region, and the
blackbody component as emission from the inner accretion disk. The broad
feature in the iron line region is compatible with reflection from the inner
accretion disk.Comment: 8 pages, 10 figures, accepted for publication by A&
A relativistic iron emission line from the neutron star low-mass X-ray binary GX 3+1
We present the results of a spectroscopic study of the Fe K{\alpha} emission
of the persistent neutron-star atoll low-mass X-ray binary and type I X-ray
burster GX 3+1 with the EPIC-PN on board XMM-Newton. The source shows a flux
modulation over several years and we observed it during its fainter phase,
which corresponds to an X-ray luminosity of Lx~10^37 ergs/s. When fitted with a
two-component model, the X-ray spectrum shows broad residuals at \sim6-7 keV
that can be ascribed to an iron K{\alpha} fluorescence line. In addition, lower
energy features are observed at \sim3.3 keV, \sim3.9 keV and might originate
from Ar XVIII and Ca XIX. The broad iron line feature is well fitted with a
relativistically smeared profile. This result is robust against possible
systematics caused by instrumental pile-up effects. Assuming that the line is
produced by reflection from the inner accretion disk, we infer an inner disk
radius of \sim25 Rg and a disk inclination of 35{\deg} < i < 44{\deg}.Comment: 4 pages, 3 figures Accepted for publication in Astronomy and
Astrophysic
Disc-Jet coupling in the LMXB 4U1636-53 from INTEGRAL
We report on the spectral analysis results of the neutron star, atoll type,
low mass X-ray Binary 4U1636-53 observed by INTEGRAL and BeppoSAX satellites.
Spectral behavior in three different epochs corresponding to three different
spectral states has been deeply investigated. Two data set spectra show a
continuum well described by one or two soft blackbody plus a Comptonized
components with changes in the Comptonizing electrons and black body
temperature and the accretion rates, which are typical of the spectral
transitions from high to low state. In one occasion INTEGRAL spectrum shows,
for first time in this source, a hard tail dominating the emission above 30
keV. The total spectrum is fitted as the sum of a Comptonized component similar
to soft state and a power-law component (Gamma=2.76), indicating the presence
of a non thermal electron distribution of velocities. In this case, a
comparison with hard tails detected in soft states from neutron stars systems
and some black hole binaries suggests that a similar mechanism could originate
these components in both cases.Comment: 6 pages, 4 figures, 2 tables. accepted Ap
Testing reflection features in 4U 1705-44 with XMM-Newton, BeppoSAX and RXTE in the hard and soft state
We use data of the bright atoll source 4U 1705-44 taken with XMM-Newton,
BeppoSAX and RXTE both in the hard and in the soft state to perform a
self-consistent study of the reflection component in this source. Although the
data from these X-ray observatories are not simultaneous, the spectral
decomposition is shown to be consistent among the different observations, when
the source flux is similar. We therefore select observations performed at
similar flux levels in the hard and soft state in order to study the spectral
shape in these two states in a broad band (0.1-200 keV) energy range, with good
energy resolution, and using self-consistent reflection models. These
reflection models provide a good fit for the X-ray spectrum both in the hard
and in the soft state in the whole spectral range. We discuss the differences
in the main spectral parameters we find in the hard and the soft state,
respectively, providing evidence that the inner radius of the optically thick
disk slightly recedes in the hard state.Comment: Accepted for publication in A&A, 20 pages, 12 figure
SAXJ1712.6-3739: a persistent hard X-ray source as monitored with INTEGRAL
The X-ray source SAXJ1712.6-3739 is a very weak Low Mass X-ray Binary
discovered in 1999 with BeppoSAX and located in the Galactic Center. This
region has been deeply investigated by the INTEGRAL satellite with an
unprecedented exposure time, giving us an unique opportunity to study the hard
X-ray behavior also for weak objects. The spectral results are based on the
systematic analysis of all INTEGRAL observations covering the source position
performed between February 2003 and October 2006. SAXJ1712.6-3739 did not shows
any flux variation along this period as well as compared to previous BeppoSAX
observation. Hence, to better constrain the physical parameters we combined
both instrument data. Long INTEGRAL monitoring reveals, for the first time,
that this X-ray burster is a weak persistent source, displaying a X-ray
spectrum extended to high energy and spending most of the time in a low
luminosity hard state. The broad-band spectrum is well modeled with a simple
Comptonized model with a seed photons temperature of ~0.5keV and an electron
temperature of ~24keV. The low mass accretion rate (~2x10^{-10} Msun/yr), the
long bursts recurrence time, the small sizes of the region emitting the seed
photons consisting with the inner disk radius and the high luminosity ratio in
the 40-100keV and 20-40keV band, are all features common to the Ultra Compact
source class.Comment: accepted A&
Jellyfish Impacts on Marine Aquaculture and Fisheries
Over the last 50 years there has been an increased frequency and severity of negative impacts affecting marine fishery and aquaculture sectors, which claimed significant economic losses due to the interference of stinging gelatinous organisms with daily operational activities. Nevertheless, original scientific information on jellyfish-related incidents, their consequences, and potential preventative and mitigation countermeasures is limited and scattered across gray literature, governmental technical reports, and communication media. A literature scan searching for records of any interactions between jellyfish and the marine fishery/aquaculture sectors was carried out. Out of 553 papers, 90 contained original information, referring to more than 130 cases worldwide of negative impacts of jellyfish on marine fishery/aquaculture over the last century. Calling attention on too often neglected socio-economic and ecological impacts of jellyfish blooms, the purpose of this paper is to review and analyze the most up-to-date research on this subject and to provide a global perspective on the importance of jellyfish impacts and their cascading effects on marine fishery and aquaculture sectors
The reflection component in NS LMXBs
Thanks to the good spectral resolution and large effective area of the EPIC/PN instrument on board of XMM-Newton, we have at hand a large number of observations of accreting low-mass X-ray binaries, that allow for the fist time a comprehensive view on the characteristics of the reflection component at different accretion regimes and to probe the effects of a magnetosphere on its formation. We focus here on a comparative analysis of the reflection component from a series of spectroscopic studies on selected sources: 4U 1705-44, observed both in the soft and hard state, the pulsating ms pulsars SAX J1808.4-3658 and IGR J17511-3057, and the intermittent pulsar HETE J1900-2455. Although the sources can present very similar accretion rates and continuum shapes, the reflection parameters do not generally result the same, moreover the effect of a magnetosphere on the formation of the reflection component appears elusive. \ua9 2014 Owned by the authors
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