186 research outputs found
Multifrequency Observations of the Blazar 3C 279 in January 2006
We report first results of a multifrequency campaign from radio to hard X-ray
energies of the prominent gamma-ray blazar 3C 279, which was organised around
an INTEGRAL ToO observation in January 2006, and triggered on its optical
state. The variable blazar was observed at an intermediate optical state, and a
well-covered multifrequency spectrum from radio to hard X-ray energies could be
derived. The SED shows the typical two-hump shape, the signature of non-thermal
synchrotron and inverse-Compton (IC) emission from a relativistic jet. By the
significant exposure times of INTEGRAL and Chandra, the IC spectrum (0.3 - 100
keV) was most accurately measured, showing - for the first time - a possible
bending. A comparison of this 2006 SED to the one observed in 2003, also
centered on an INTEGRAL observation, during an optical low-state, reveals the
surprising fact that - despite a significant change at the high-energy
synchrotron emission (near-IR/optical/UV) - the rest of the SED remains
unchanged. In particular, the low-energy IC emission (X- and hard X-ray
energies) remains the same as in 2003, proving that the two emission components
do not vary simultaneously, and provides strong constraints on the modelling of
the overall emission of 3C 279.Comment: 4 pages, 6 figures; to be published in the Proc. of the 6th INTEGRAL
workshop "The Obscured Universe" (Moscow, July 2-8, 2006), eds. S. Grebenev,
R. Sunyaev, C. Winkler, ESA SP 622 (2006
Multifrequency Observations of the Gamma-Ray Blazar 3C 279 in Low-State during Integral AO-1
We report first results of a multifrequency campaign from radio to hard X-ray
energies of the prominent gamma-ray blazar 3C 279 during the first year of the
INTEGRAL mission. The variable blazar was found at a low activity level, but
was detected by all participating instruments. Subsequently a multifrequency
spectrum could be compiled. The individual measurements as well as the compiled
multifrequency spectrum are presented. In addition, this 2003 broadband
spectrum is compared to one measured in 1999 during a high activity period of
3C 279.Comment: 4 pages including 6 figures, to appear in: 'Proc. of the 5th INTEGRAL
Workshop', ESA SP-552, in pres
Peculiar outburst of A 0535+26 observed with INTEGRAL, RXTE and Suzaku
A normal outburst of the Be/X-ray binary system A0535+26 has taken place in
August 2009. It is the fourth in a series of normal outbursts that have occured
around the periastron passage of the source, but is unusual by starting at an
earlier orbital phase and by presenting a peculiar double-peaked light curve. A
first "flare" (lasting about 9 days from MJD 55043 on) reached a flux of 440
mCrab. The flux then decreased to less than 220 mCrab, and increased again
reaching 440 mCrab around the periastron at MJD 55057. Target of Opportunity
observations have been performed with INTEGRAL, RXTE and Suzaku. First results
of these observations are presented, with special emphasis on the cyclotron
lines present in the X-ray spectrum of the source, as well as in the pulse
period and energy dependent pulse profiles of the source.Comment: 6 pages, Accepted for publication on PoS, Proceedings of "The Extreme
sky: Sampling the Universe above 10 keV", held in Otranto (Italy) in October
200
A 0535+26 in the August/September 2005 outburst observed by RXTE and INTEGRAL
In this Letter we present results from INTEGRAL and RXTE observations of the
spectral and timing behavior of the High Mass X-ray Binary A 0535+26 during its
August/September 2005 normal (type I) outburst with an average flux
F(5-100keV)~400mCrab. The search for cyclotron resonance scattering features
(fundamental and harmonic) is one major focus of the paper. Our analysis is
based on data from INTEGRAL and RXTE Target of Opportunity Observations
performed during the outburst. The pulse period is determined. X-ray pulse
profiles in different energy ranges are analyzed. The broad band INTEGRAL and
RXTE pulse phase averaged X-ray spectra are studied. The evolution of the
fundamental cyclotron line at different luminosities is analyzed. The pulse
period P is measured to be 103.39315(5)s at MJD 53614.5137. Two absorption
features are detected in the phase averaged spectra at E_1~45keV and
E_2~100keV. These can be interpreted as the fundamental cyclotron resonance
scattering feature and its first harmonic and therefore the magnetic field can
be estimated to be B~4x10^12G.Comment: 4 pages, 5 figures, accepted for publication in A&A Letter
The pre-outburst flare of the A 0535+26 August/September 2005 outburst
We study the spectral and temporal behavior of the High Mass X-ray Binary A
0535+26 during a `pre-outburst flare' which took place ~5 d before the peak of
a normal (type I) outburst in August/September 2005. We compare the studied
behavior with that observed during the outburst. We analyse RXTE observations
that monitored A 0535+26 during the outburst. We complete spectral and timing
analyses of the data. We study the evolution of the pulse period, present
energy-dependent pulse profiles both at the initial pre-outburst flare and
close to outburst maximum, and measure how the cyclotron resonance-scattering
feature (hereafter CRSF) evolves. We present three main results: a constant
period P=103.3960(5)s is measured until periastron passage, followed by a
spin-up with a decreasing period derivative of Pdot=(-1.69+/-0.04)x10^(-8)s/s
at MJD 53618, and P remains constant again at the end of the main outburst. The
spin-up provides evidence for the existence of an accretion disk during the
normal outburst. We measure a CRSF energy of Ecyc~50kev during the pre-outburst
flare, and Ecyc~46kev during the main outburst. The pulse shape, which varies
significantly during both pre-outburst flare and main outburst, evolves
strongly with photon energy.Comment: 4 pages, 4 figures, accepted for publication in A&A Letters. To be
published in parallel to Postnov et al. 200
Magnetic Fields of Accreting X-Ray Pulsars with the Rossi X-Ray Timing Explorer
Using a consistent set of models, we parameterized the X-ray spectra of all
accreting pulsars in the Rossi X-ray Timing Explorer database which exhibit
Cyclotron Resonance Scattering Features (CRSFs, or cyclotron lines). These
sources in our sample are Her X-1, 4U 0115+63, Cen X-3, 4U 1626-67, XTE
J1946-274, Vela X-1, 4U 1907+09, 4U 1538-52, GX 301-2, and 4U 0352+309 (X Per).
We searched for correlations among the spectral parameters, concentrating on
how the cyclotron line energy relates to the continuum and therefore how the
neutron star B-field influences the X-Ray emission. As expected, we found a
correlation between the CRSF energy and the spectral cutoff energy. However,
with our consistent set of fits we found that the relationship is more complex
than what has been reported previously. Also, we found that not only does the
width of the cyclotron line correlate with the energy (as suggested by theory),
but that the width scaled by the energy correlates with the depth of the
feature. We discuss the implications of these results, including the
possibility that accretion directly affects the relative alignment of the
neutron star spin and dipole axes. Lastly, we comment on the current state of
fitting phenomenological models to spectra in the RXTE/BeppoSAX era and the
need for better theoretical models of the X-Ray continua of accreting pulsars.Comment: 36 Pages, 9 Figures, 9 Tables, ApJ in pres
Small-world networks: Evidence for a crossover picture
Watts and Strogatz [Nature 393, 440 (1998)] have recently introduced a model
for disordered networks and reported that, even for very small values of the
disorder in the links, the network behaves as a small-world. Here, we test
the hypothesis that the appearance of small-world behavior is not a
phase-transition but a crossover phenomenon which depends both on the network
size and on the degree of disorder . We propose that the average
distance between any two vertices of the network is a scaling function
of . The crossover size above which the network behaves as a
small-world is shown to scale as with .Comment: 5 pages, 5 postscript figures (1 in color),
Latex/Revtex/multicols/epsf. Accepted for publication in Physical Review
Letter
The INTEGRAL view of the Soft Gamma-ray Repeater SGR 1806-20
We present the results obtained by INTEGRAL on the Soft-Gamma Ray Repeater
SGR 1806-20. In particular we report on the temporal and spectral properties of
the bursts detected during a moderately active period of the source in
September and October 2003 and on the search for quiescent emission.Comment: To appear in the proceedings (ESA-SP) of the 5th INTEGRAL Workshop,
"The INTEGRAL UNIVERSE", Munich, 16-20 February 200
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