329 research outputs found
XMM-Newton study of the persistent X-ray source 1E1743.1-2843 located in the Galactic Center direction
We report the results of an XMM-Newton observation of the persistent X-ray
source 1E1743.1-2843, located in the Galactic Center (GC) direction. We
determine the position of the source at alpha_J2000=17h46m21.0s,
delta_J2000=-28deg43'44" (with an uncertainty of 1.5"), which is the most
accurate to date, and will enable cross-identifications at other wavelengths.
The source was bright during this observation (L_2-10keV ~ 2.7 x 10^36
d^2_10kpc erg/s for a power-law continuum), with no significant variability. We
propose that 1E1743.1-2843 may be explained in terms of a black hole candidate
in a low/hard state. There is an indication that the source exhibits different
states from a comparison of our results with previous observations (e.g.,
ART-P, BeppoSAX). However, the present spectral analysis does not rule out the
hypothesis of a neutron star low-mass X-ray binary as suggested previously. If
1E1743.1-2843 is actually located in the GC region, we might expect to observe
significant 6.4keV fluorescent iron line emission from nearby molecular clouds
(e.g., GCM+0.25+0.01).Comment: 6 pages; accepted for publication in A&
High-Resolution spectroscopy of the low-mass X-ray binary EXO 0748-67
We present initial results from observations of the low-mass X-ray binary EXO
0748-67 with the Reflection Grating Spectrometer on board the XMM-Newton
Observatory. The spectra exhibit discrete structure due to absorption and
emission from ionized neon, oxygen, and nitrogen. We use the quantitative
constraints imposed by the spectral features to develop an empirical model of
the circumsource material. This consists of a thickened accretion disk with
emission and absorption in the plasma orbiting high above the binary plane.
This model presents challenges to current theories of accretion in X-ray binary
systems.Comment: 5 pages, 4 figures, accepted by A&A letters, XMM special issu
The X-ray flaring activity of the galactic nucleus observed with XMM-Newton
We report the results of XMM-Newton observations of Sgr A*, the radiative
counterpart of the massive black hole at the nucleus of our Galaxy, performed
in the frame of the guaranteed time survey program of the Galactic Center
region. The discovery of bright X-ray flares from Sgr A* with Chandra in
October 2000 have opened new perspectives to understand the processes at work
in this object and in general in black holes accreting at low accretion rates.
We report here the important results obtained with XMM-Newton on the Sgr A*
high-energy flaring activity and we discuss the implications on the models and
the future observational perspectives.Comment: 4 pages, 3 figures, proc. of the SF2A conf. held in Bordeaux, France,
June 2003, eds.: F. Combes, D. Barret and T. Contini, EdP-Sciences Conf.
Serie
Tidal Capture by a Black Hole and Flares in Galactic Centres
We present the telltale signature of the tidal capture and disruption of an
object by a massive black hole in a galactic centre. As a result of the
interaction with the black hole's strong gravitational field, the object's
light curve can flare-up with characteristic time of the order of 100 sec
\times (M_{bh} / 10^6 M_{Solar}). Our simulations show that general relativity
plays a crucial role in the late stages of the encounter in two ways: (i) due
to the precession of perihelion, tidal disruption is more severe, and (ii)
light bending and aberration of light produce and enhance flares seen by a
distant observer. We present our results for the case of a tidally disrupted
Solar-type star. We also discuss the two strongest flares that have been
observed at the Galactic centre. Although the first was observed in X-rays and
the second in infra-red, they have almost identical light curves and we find it
interesting that it is possible to fit the infra-red flare with a rather simple
model of the tidally disrupted comet-like or planetary object. We discuss the
model and possible scenarios how such an event can occur.Comment: 3 pages, 1 figur
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