446 research outputs found
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
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&
IGR J22517+2218=MG3 J225155+2217: a new gamma-ray lighthouse in the distant Universe
We report on the identification of a new soft gamma ray source, namely IGR
J22517+2218, detected with IBIS/INTEGRAL. The source, which has an observed
20-100 keV flux of ~4 x10^-11 erg cm-2 s-1, is spatially coincident with MG3
J225155+2217, a quasar at z=3.668. The Swift/XRT 0.5-10 keV continuum is flat
(Gamma=1.5) with evidence for a spectral curvature below 1-2 keV either due to
intrinsic absorption (NH=3 +/- 2 x 10^22 cm-2) or to a change in slope (Delta
Gamma= 0.5). X-ray observations indicate flux variability over a 6 days period
which is further supported by a flux mismatch between Swift and INTEGRAL
spectra. IGR J22517+2218 is radio loud and has a flat radio spectrum; optically
it is a broad line emitting quasar with the atypical property of hosting a
narrow line absorption system. The Source Spectral Energy Distribution is
unusual compared to blazars of similar type: either it has the synchrotron peak
in the X/gamma-ray band (i.e. much higher than generally observed) or the
Compton peak in the MeV range (i.e. lower than typically measured). IGR
J22517+2218=MG3 J225155+2217 is the second most distant blazar detected above
20 keV and a gamma-ray lighthouse shining from the edge of our Universe.Comment: 4 pages, 4 figures, Accepted for publication in Astrophysical Journal
Letter
An active state of the BL Lac Object Markarian 421 detected by INTEGRAL in April 2013
Multiwavelength variability of blazars offers indirect insight into their
powerful engines and on the mechanisms through which energy is propagated from
the centre down the jet. The BL Lac object Mkn 421 is a TeV emitter, a bright
blazar at all wavelengths, and therefore an excellent target for variability
studies. Mkn 421 was observed by INTEGRAL and Fermi-LAT in an active state on
16-21 April 2013. Well sampled optical, soft, and hard X-ray light curves show
the presence of two flares. The average flux in the 20-100 keV range is 9.1e-11
erg/s/cm2 (~4.5 mCrab) and the nuclear average apparent magnitude, corrected
for Galactic extinction, is V ~12.2. In the time-resolved X-ray spectra (3.5-60
keV), which are described by broken power laws and, marginally better, by
log-parabolic laws, we see a hardening that correlates with flux increase, as
expected in refreshed energy injections in a population of electrons that later
cool via synchrotron radiation. The hardness ratios between the JEM-X fluxes in
two different bands and between the JEM-X and IBIS/ISGRI fluxes confirm this
trend. During the observation, the variability level increases monotonically
from the optical to the hard X-rays, while the large LAT errors do not allow a
significant assessment of the MeV-GeV variability. The cross-correlation
analysis during the onset of the most prominent flare suggests a monotonically
increasing delay of the lower frequency emission with respect to that at higher
frequency, with a maximum time-lag of about 70 minutes, that is however not
well constrained. The spectral energy distributions from the optical to the TeV
domain are satisfactorily described by homogeneous models of blazar emission
based on synchrotron radiation and synchrotron self-Compton scattering, except
in the state corresponding to the LAT softest spectrum and highest flux.Comment: 11 pages, 6 figures, in press in A&
XMM-Newton Observations of the Field of Gamma-Ray Burst 980425
The error box of GRB980425 has been observed by XMM-Newton in March 2002,
with the aim of measuring the late epoch X-ray emission of the supernova 1998bw
and of clarifying its supposed association with the GRB itself. We present here
the preliminary results obtained with the EPIC PN camera. Our observations
confirm the association between SN 1998bw and GRB980425. The EPIC PN
measurement of the SN 1998bw flux is significantly below the extrapolation of
the power-law temporal trend fitted to the BeppoSAX points and implies a faster
temporal decay. We propose different physical interpretations of the SN X-ray
light curve, according to whether it is produced by one or more radiation
components.Comment: 5 pages, 2 figures; in press in Adv. Sp. Res., Proceedings of the
34th COSPAR Scientific Assembly, Houston, 10-19 October 200
Spectral states evolution of 4U 1728-34 observed by INTEGRAL and RXTE: non-thermal component detection
We report results of a one-year monitoring of the low mass X-ray binary
(LMXB) source (atoll type) 4U 1728-34 with INTEGRAL and RXTE. Three time
intervals were covered by INTEGRAL, during which the source showed strong
spectral evolution. We studied the broad-band X-ray spectra in detail by
fitting several models in the different sections of the hardness-intensity
diagram. The soft states are characterised by prominent blackbody emission plus
a contribution from a Comptonized emission. The hard states are characterised
by the presence of an excess flux with respect to the Comptonization model
above 50 keV while the soft component is fainter. To obtain an acceptable fit
to the data this excess is modeled either with a power law with photon index
Gamma ~ 2 or a Comptonization (CompPS) spectrum implying the presence of hybrid
thermal and non-thermal electrons in a corona. This makes 4U 1728-34 one of the
few LMXBs of atoll type showing non-thermal emission at high energy. From our
analysis, it is also apparent that the presence of the hard tail is more
prominent as the overall spectrum becames harder. We discuss also alternative
models which can discribe these hard states.Comment: Accepted for publication in MNRAS (accepted 2011 April 20. Received
2011 April 20; in original form 2010 December 07); 9 pages, 7 figure
Probing restarting activity in hard X-ray selected giant radio galaxies
With their sizes larger than 0.7 Mpc, Giant Radio Galaxies (GRGs) are the
largest individual objects in the Universe. To date, the reason why they reach
such enormous extensions is still unclear. One of the proposed scenarios
suggests that they are the result of multiple episodes of jet activity.
Cross-correlating the INTEGRAL+Swift AGN population with radio catalogues
(NVSS, FIRST, SUMSS), we found that 22% of the sources are GRG (a factor four
higher than those selected from radio catalogues). Remarkably, 80% of the
sample shows signs of restarting radio activity. The X-ray properties are
consistent with this scenario, the sources being in a high-accretion,
high-luminosity state with respect to the previous activity responsible for the
radio lobes.Comment: To appear soon as a proceeding of the XXXth IAU General Assembly,
Focus Meeting 3 "Radio Galaxies: Resolving the AGN phenomenon
Extracts of Feijoa Inhibit Toll-Like Receptor 2 Signaling and Activate Autophagy Implicating a Role in Dietary Control of IBD
Inflammatory bowel disease (IBD) is a heterogeneous chronic inflammatory disease affecting the gut with limited treatment success for its sufferers. This suggests the need for better understanding of the different subtypes of the disease as well as nutritional interventions to compliment current treatments. In this study we assess the ability of a hydrophilic feijoa fraction (F3) to modulate autophagy a process known to regulate inflammation, via TLR2 using IBD cell lines
Multiwavelength observations of 3C 454.3. I. The AGILE 2007 November campaign on the "Crazy Diamond"
[Abridged] We report on a multiwavelength observation of the blazar 3C 454.3
(which we dubbed "crazy diamond") carried out on November 2007 by means of the
astrophysical satellites AGILE, INTEGRAL, Swift, the WEBT Consortium, and the
optical-NIR telescope REM. 3C 454.3 is detected at a level
during the 3-week observing period, with an average flux above 100 MeV of
\phcmsec. The gamma-ray
spectrum can be fit with a single power-law with photon index between 100 MeV and 1 GeV. We detect significant
day-by-day variability of the gamma-ray emission during our observations, and
we can exclude that the fluxes are constant at the 99.6% ()
level. The source was detected typically around 40 degrees off-axis, and it was
substantially off--axis in the field of view of the AGILE hard X-ray imager.
However, a 5-day long ToO observation by INTEGRAL detected 3C 454.3 at an
average flux of about \phcmsec with
an average photon index of between 20--200
keV. Swift also detected 3C 454.3 with a flux in the 0.3--10 keV energy band in
the range \phcmsec{} and a photon index in the
range . In the optical band, both WEBT and REM
show an extremely variable behavior in the band. A correlation analysis
based on the entire data set is consistent with no time-lags between the
gamma-ray and the optical flux variations. Our simultaneous multifrequency
observations strongly indicate that the dominant emission mechanism between 30
MeV and 30 GeV is dominated by inverse Compton scattering of relativistic
electrons in the jet on the external photons from the broad line region.Comment: Accepted for publication in ApJ. Abridged Abstract. 37 pages, 14
Figures, 3 Table
The brightest gamma-ray flaring blazar in the sky: AGILE and multi-wavelength observations of 3C 454.3 during November 2010
Since 2005, the blazar 3C 454.3 has shown remarkable flaring activity at all
frequencies, and during the last four years it has exhibited more than one
gamma-ray flare per year, becoming the most active gamma-ray blazar in the sky.
We present for the first time the multi-wavelength AGILE, SWIFT, INTEGRAL, and
GASP-WEBT data collected in order to explain the extraordinary gamma-ray flare
of 3C 454.3 which occurred in November 2010. On 2010 November 20 (MJD 55520),
3C 454.3 reached a peak flux (E>100 MeV) of F_gamma(p) = (6.8+-1.0)E-5 ph/cm2/s
on a time scale of about 12 hours, more than a factor of 6 higher than the flux
of the brightest steady gamma-ray source, the Vela pulsar, and more than a
factor of 3 brighter than its previous super-flare on 2009 December 2-3. The
multi-wavelength data make a thorough study of the present event possible: the
comparison with the previous outbursts indicates a close similarity to the one
that occurred in 2009. By comparing the broadband emission before, during, and
after the gamma-ray flare, we find that the radio, optical and X-ray emission
varies within a factor 2-3, whereas the gamma-ray flux by a factor of 10. This
remarkable behavior is modeled by an external Compton component driven by a
substantial local enhancement of soft seed photons.Comment: Accepted for publication in ApJ Letters. 18 Pages, 4 Figures, 1 Tabl
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