4,446 research outputs found
Unveiling the Nature of the High Energy Source IGR J19140+0951
We report on high energy observations of IGR J19140+0951 performed with RXTE
on three occasions in 2002, 2003 and 2004, and INTEGRAL during a very well
sampled and unprecedented high energy coverage of this source from early-March
to mid-May 2003. Our analysis shows that IGR J19140+0951 spends most of its
time in a very low luminosity state, probably corresponding to the state
observed with RXTE, and characterised by thermal Comptonisation. In some
occasions we observe variations of the luminosity by a factor of about 10
during which the spectrum can show evidence for a thermal component, besides
thermal Comptonisation by a hotter plasma than during the low luminosity state.
The spectral parameters obtained from the spectral fits to the INTEGRAL and
RXTE data strongly suggest that IGR J19140+0951 hosts a neutron star rather
than a black hole. Very importantly, we observe variations of the absorption
column density (with a value as high as ~10^23 cm^-2). Our spectral analysis
also reveals a bright iron line detected with both RXTE/PCA and INTEGRAL/JEM-X,
at different levels of luminosity. We discuss these results and the behaviour
of IGR J19140+0951, and show, by comparison with other well known systems (Vela
X-1, GX 301-2, 4U 2206+54), that IGR J19140+0951 is most probably a High Mass
X-ray Binary.Comment: Accepted for publication in Astronomy and Astrophysics. 13 pages, 6
figure
Multi-wavelength INTEGRAL NEtwork (MINE) observations of the microquasar GRS 1915+105
We present the international collaboration MINE (Multi-lambda Integral
NEtwork) aimed at conducting multi-wavelength observations of X-ray binaries
and microquasars simultaneously with the INTEGRAL gamma-ray satellite. We will
focus on the 2003 March-April campaign of observations of the peculiar
microquasar GRS 1915+105 gathering radio, IR and X-ray data. The source was
observed 3 times in the plateau state, before and after a major radio and X-ray
flare. It showed strong steady optically thick radio emission corresponding to
powerful compact jets resolved in the radio images, bright near-infrared
emission, a strong QPO at 2.5 Hz in the X-rays and a power law dominated
spectrum without cutoff in the 3-300 keV range. We compare the different
observations, their multi-wavelength light curves, including JEM-X, ISGRI and
SPI, and the parameters deduced from fitting the spectra obtained with these
instruments on board INTEGRAL.Comment: 4 pages, 9 fig., Proc. of the 5th INTEGRAL Workshop (Feb. 16-20
2004), to be published by ES
Simultaneous multi-wavelength observations of microquasars (the MINE collaboration)
We present the international collaboration MINE (Multi-lambda INTEGRAL
NEtwork) aimed at conducting multi-wavelength observations of microquasars
simultaneously with the INTEGRAL satellite. The first results on GRS 1915+105
are encouraging and those to come should help us to understand the physics of
the accretion and ejection phenomena around a compact object.Comment: 2 p, 3 fig., proc. of the IAU Coll. 194, ``Compact Binaries in the
Galaxy and Beyond'', Nov. 2003, La Paz, Mexico, to be published in the Conf.
Series of Revista Mexicana de Astronomia y Astrofisica, Eds. G. Tovmassian &
E. Sio
Characterizing a new class of variability in GRS 1915+105 with simultaneous INTEGRAL/RXTE observations
We report on the analysis of 100 ks INTEGRAL observations of the Galactic
microquasar GRS 1915+105. We focus on INTEGRAL Revolution number 48 when the
source was found to exhibit a new type of variability as preliminarily reported
in Hannikainen et al. (2003). The variability pattern, which we name , is
characterized by a pulsing behaviour, consisting of a main pulse and a shorter,
softer, and smaller amplitude precursor pulse, on a timescale of 5 minutes in
the JEM-X 3-35 keV lightcurve. We also present simultaneous RXTE data. From a
study of the individual RXTE/PCA pulse profiles we find that the rising phase
is shorter and harder than the declining phase, which is opposite to what has
been observed in other otherwise similar variability classes in this source.
The position in the colour-colour diagram throughout the revolution corresponds
to State A (Belloni et al. 2000) but not to any previously known variability
class. We separated the INTEGRAL data into two subsets covering the maxima and
minima of the pulses and fitted the resulting two broadband spectra with a
hybrid thermal--non-thermal Comptonization model. The fits show the source to
be in a soft state characterized by a strong disc component below ~6 keV and
Comptonization by both thermal and non-thermal electrons at higher energies.Comment: Accepted for publication in A&A. 11 pages, 10 figures, 4 in colour.
Original figures can be found at
http://www.astro.helsinki.fi/~diana/grs1915_rev48. Author affiliations
correcte
Optical properties of quantum wires: Disorder-scattering in the Lloyd-model
The Lloyd model is extended to the exciton problem in quasi one-dimensional
structures to study the interplay between the Coulomb attraction and disorder
scattering. Within this model the averaging and resummation of the locator
series can be performed analytically. As an application, the optical absorption
in quantum box wires is investigated. Without electron-hole interaction,
fluctuations in the well-width lead to an asymmetric broadening of the
minibands with respect to the lower and upper band-edges.Comment: 7 pages, 6 figure
Simultaneous multi-wavelength observations of GRS 1915+105
We present the result of multi-wavelength observations of the microquasar GRS
1915+105 in a plateau state with a luminosity of ~7.5x10^{38) erg s-1 (~40%
L_Edd), conducted simultaneously with the INTEGRAL and RXTE satellites, the
ESO/NTT, the Ryle Telescope, the NRAO VLA and VLBA, in 2003 April 2-3. For the
first time were observed concurrently in GRS 1915+105 all of the following
properties: a strong steady optically thick radio emission corresponding to a
powerful compact jet resolved with the VLBA, bright near-IR emission, a strong
QPO at 2.5 Hz in the X-rays and a power law dominated spectrum without any
cutoff in the 3-400 keV range.Comment: 5 pages, 5 figures (4 colour figures), accepted by A&A Letter
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