572 research outputs found
A closer look at the X-ray transient XTE J1908+094: identification of two new near-infrared candidate counterparts
We had reported in Chaty, Mignani, Israel (2002) on the near-infrared (NIR)
identification of a possible counterpart to the black hole candidate XTE
J1908+094 obtained with the ESO/NTT. Here, we present new, follow-up, CFHT
adaptive optics observations of the XTE J1908+094 field, which resolved the
previously proposed counterpart in two objects separated by about 0.8".
Assuming that both objects are potential candidate counterparts, we derive that
the binary system is a low-mass system with a companion star which could be
either an intermediate/late type (A-K) main sequence star at a distance of 3-10
kpc, or a late-type (K) main sequence star at a distance of 1-3 kpc.
However, we show that the brighter of the two objects (J ~ 20.1, H ~ 18.7, K' ~
17.8) is more likely to be the real counterpart of the X-ray source. Its
position is more compatible with our astrometric solution, and colours and
magnitudes of the other object are not consistent with the lower limit of 3 kpc
derived independently from the peak bolometric flux of XTE J1908+094. Further
multi-wavelength observations of both candidate counterparts are crucial in
order to solve the pending identification.Comment: accepted for publication in MNRAS, 5 pages, 3 figure
Infrared study of H 1743-322 in outburst: a radio-quiet and NIR-dim microquasar
International audienceContext. Microquasars are accreting Galactic sources that are commonly observed to launch relativistic jets. One of the most important issues regarding these sources is the energy budget of ejections relative to the accretion of matter.Aims. The X-ray binary, black hole candidate, and microquasar H 1743-322 exhibited a series of X-ray outbursts between 2003 and 2008. We took optical and near-infrared (OIR) observations with the ESO/NTT telescope during three of these outbursts (2003, 2004, and 2008). The goals of these observations were to investigate the presence of a jet, and to disentangle the various contributions constituting the spectral energy distribution (SED): accretion, ejection, and stellar emission.Methods. Photometric and spectroscopic OIR observations allowed us to produce a high time-resolution lightcurve in Ks-band, to analyze emission lines present in the IR spectra, to construct a multiwavelength SED including radio, IR, and X-ray data, and to complete the OIR vs. X-ray correlation of black hole binaries with H 1743-322 data points.Results. We detect rapid flares of duration ~5 min in the high time-resolution IR lightcurve. We identify hydrogen and helium emission lines in the IR spectra, coming from the accretion disk. The IR SED exhibits the spectral index typically associated with the X-ray high, soft state in our observations taken during the 2003 and 2004 outbursts, while the index changes to one that is typical of the X-ray low, hard state during the 2008 outburst. During this last outburst, we detected a change of slope in the NIR spectrum between the J and Ks bands, where the JH part is characteristic of an optically thick disk emission, while the HKs part is typical of optically thin synchrotron emission. Furthermore, the comparison of our IR data with radio and X-ray data shows that H 1743-322 exhibits a faint jet both in radio and NIR domains. Finally, we suggest that the companion star is a late-type main sequence star located in the Galactic bulge.Conclusions. These OIR photometric and spectroscopic observations of the microquasar H 1743-322, which are the first of this source to be published in a broad multiwavelength context, allow us to unambiguously identify two spectra of different origins in the OIR domain, evolving from optically thick thermal emission to optically thin synchrotron emission toward longer wavelengths. Comparing these OIR observations with other black hole candidates suggests that H 1743-322 behaves like a radio-quiet and NIR-dim black hole in the low, hard state. This study will be useful when quantitatively comparing the overall contribution of the compact jet and accretion flow in the energy budget of microquasars
Near-infrared jet emission in the microquasar XTE J1550-564
Context: Microquasars are accreting Galactic sources that are also observed
to launch relativistic jets. A key signature of the ejection is non-thermal
radio emission. The level of this jet component at high frequencies is still
poorly constrained. Aims: The X-ray binary and microquasar black hole candidate
XTE J1550-564 exhibited a faint X-ray outburst in April 2003 during which it
stayed in the X-ray low/hard state. We took optical and near-infrared (NIR)
observations with the ESO/NTT telescope during this outburst to disentangle the
various contributions to the spectral energy distribution (SED) and investigate
the presence of a jet component. Methods: Photometric and spectroscopic
observations allowed us to construct an SED and also to produce a high
time-resolution lightcurve. Results: The SED shows an abrupt change of slope
from the NIR domain to the optical. The NIR emission is attributed to
non-thermal synchrotron emission from the compact, self-absorbed jet that is
known to be present in the low/hard state. This is corroborated by the fast
variability, colours, lack of prominent spectral features and evidence for
intrinsic polarisation. The SED suggests the jet break from the optically thick
to the thin regime occurs in the NIR. Conclusions: The simultaneous optical-NIR
data allow an independent confirmation of jet emission in the NIR. The
transition to optically thin synchrotron occurs at NIR frequencies or below,
which leads to an estimated characteristic size greater than 2x10^8cm and
magnetic field less than 5T for the jet base, assuming a homogeneous one-zone
synchrotron model.Comment: Accepted for publication in Astronomy and Astrophysics (Section 7.
Stellar structure and evolution; 8 pages, 6 figures
Coronal origin of the polarization of the high-energy emission of Cygnus X-1
Cygnus X-1 is the candidate with the highest probability of containing a
black hole among the X-ray binary systems in the Galaxy. It is also by far the
most often studied of these objects. Recently, the International Gamma-Ray
Astrophysics Laboratory Imager onboard then Integral satellite ({\it
INTEGRAL}/IBIS) detected strong polarization in the high-energy radiation of
this source, between 400 keV and 2 MeV. This radiation has been attributed to a
jet launched by the black hole. We consider whether the corona around the black
hole might be the site of production of the polarized emission instead of the
jet. We studied self-consistently the injection of nonthermal particles in the
hot, magnetized plasma around the black hole. We show that both the high-energy
spectrum and polarization of Cygnus X-1 in the low-hard state can originate in
the corona, without needing to invoke a jet. We estimate the degree of
polarization in the intermediate state, where there is no jet, to provide a
tool to test our model. Contrary to the commonly accepted view, the jet might
not be the source of the MeV polarized tail in the spectrum of Cygnus X-1.Comment: 4 pages, 2 figures, accepted in A&A Letter
A Search for the Optical/Infrared Counterpart of the Anomalous X-ray Pulsar 1E 1841-045
We have carried out a search for the optical and infrared counterpart of the
Anomalous X-ray Pulsar 1E 1841-045, which is located at the center of the
supernova remnant Kes73. We present the first deep optical and infrared images
of the field of 1E 1841-045, as well as optical spectroscopy results that
exclude the brightest objects in the error circle as possible counterparts. A
few of the more reddened objects in this region can be considered as
particularly interesting candidates, in consideration of the distance and
absorption expected from the association with Kes73. The strong interstellar
absorption in the direction of the source does not allow to completely exclude
the presence of main sequence massive companions.Comment: 8 pages, latex, 6 figures, Submitted to Mon. Not. R. Astron. So
Characterising anomalous transport in accretion disks from X-ray observations
Whilst direct observations of internal transport in accretion disks are not yet possible, measurement of the energy emitted from accreting astrophysical systems can provide useful information on the physical mechanisms at work. Here we examine the unbroken multi-year time variation of the total X-ray flux from three sources: Cygnus X-1 , the microquasar GRS 1915+105 , and for comparison the nonaccreting Crab nebula. To complement previous analyses, we demonstrate that the application of advanced statistical methods to these observational time-series reveals important contrasts in the nature and scaling properties of the transport processes operating within these sources. We find the Crab signal resembles Gaussian noise; the Cygnus X-1 signal is a leptokurtic random walk whose self-similar properties persist on timescales up to three years; and the GRS 1915+105 signal is similar to that from Cygnus X-1, but with self-similarity extending possibly to only a few days. This evidence of self-similarity provides a robust quantitative characterisation of anomalous transport occuring within the systems
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
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