5,759 research outputs found
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
Results and prospects on registration of reflected Cherenkov light of EAS from cosmic particles above 10^{15} eV
We give an overview of the SPHERE experiment based on detection of reflected
Vavilov-Cherenkov radiation (Cherenkov light) from extensive air showers in the
energy region E>10^{15} eV. A brief history of the reflected Cherenkov light
technique is given; the observations carried out with the SPHERE-2 detector are
summarized; the methods of the experimental datasample analysis are described.
The first results on the primary cosmic ray all-nuclei energy spectrum and mass
composition are presented. Finally, the prospects of the SPHERE experiment and
the reflected Cherenkov light technique are given.Comment: 4 pages, 3 figures, Proc. PANIC-201
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
Low temperature structural phase transition and incommensurate lattice modulation in the spin gap compound BaCuSi2O6
Results of high resolution x-ray diffraction experiments are presented for
single crystals of the spin gap compound BaCuSiO in the temperature
range from 16 to 300 K. The data show clear evidence of a transition from the
room temperature tetragonal phase into an incommensurately modulated
orthorhombic structure below 100 K. This lattice modulation is
characterized by a resolution limited wave vector {\bf
q}=(0,0.13,0) and its 2 and 3 harmonics. The phase
transition is first order and exhibits considerable hysteresis. This
observation implies that the spin Hamiltonian representing the system is more
complex than originally thought.Comment: 4 pages, 4 figure
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
INTEGRAL observations of the Small Magellanic Cloud
The first INTEGRAL observations of the Small Magellanic Cloud (carried out in
2003) are reported in which two sources are clearly detected. The first source,
SMC X-1, shows a hard X-ray eclipse and measurements of its pulse period
indicate a continuation of the long-term spin-up now covering ~30 years. The
second source is likely to be a high mass X-ray binary, and shows a potential
periodicity of 6.8s in the IBIS lightcurve. An exact X-ray or optical
counterpart cannot be designated, but a number of proposed counterparts are
discussed. One of these possible counterparts shows a strong coherent optical
modulation at ~2.7d, which, together with the measured hard X-ray pulse period,
would lead to this INTEGRAL source being classified as the fourth known high
mass Roche lobe overflow system.Comment: Accepted for publication in MNRA
On the nature of the ultraluminous X-ray transient in Cen~A (NGC 5128)
We combine 9 ROSAT, 9 Chandra, and 2 XMM-Newton observations of the Cen~A
galaxy to obtain the X-ray light curve of 1RXH J132519.8-430312 (=CXOU
J132519.9430317) spanning 1990 to 2003. The source reached a peak 0.1-2.4
keV flux F_X>10^{-12} ergs cm^{-2} s^{-1} during a 10~day span in 1995 July.
The inferred peak isotropic luminosity of the source therefore exceeded 3
10^{39} ergs s^{-1}, which places the source in the class of ultra-luminous
X-ray sources. Coherent pulsations at 13.264 Hz are detected during a second
bright episode (F_X >3 times 10^{-13} ergs cm^{-2} s^{-1}) in 1999 December.
The source is detected and varies significantly within three additional
observations but is below the detection threshold in 7 observations. The X-ray
spectrum in 1999 December is best described as a cut-off power law or a
disk-blackbody (multi-colored disk). We also detect an optical source, m_F555W
~ 24.1 mag, within the Chandra error circle of 1RXH J132519.8-430312 in HST
images taken 195~days before the nearest X-ray observation. The optical
brightness of this source is consistent with a late O or early B star at the
distance of Cen A. If the optical source is the counterpart, then the X-ray and
optical behavior of 1RXH J132519.8-430312 are similar to the transient Be/X-ray
pulsar A 0538-66.Comment: 7 pages, 8 figures. ApJ (accepted
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