7,586 research outputs found
From Multiwavelength to Mass Scaling: Accretion and Ejection in Microquasars and AGN
A solid theoretical understanding of how inflowing, accreting plasma around
black holes and other compact objects gives rise to outflowing winds and jets
is still lacking, despite decades of observations. The fact that similar
processes and morphologies are observed in both X-ray binaries as well as
active galactic nuclei has led to suggestions that the underlying physics could
scale with black hole mass, which could provide a new handle on the problem. In
the last decade, simultaneous broadband campaigns of the fast-varying X-ray
binaries particularly in their microquasar state have driven the development
of, and in some cases altered, our ideas about the inflow/outflow connection in
accreting black holes. Specifically the discovery of correlations between the
radio, infrared and X-ray bands has revealed a remarkable connectivity between
the various emission regions, and argued for a more holistic approach to
tackling questions about accretion. This article reviews the recent major
observational and theoretical advances that focus specifically on the relation
between the two "sides" of the accretion process in black holes, with an
emphasis on how new tools can be derived for comparisons across the mass scale.Comment: 31 pages, 6 figures, To appear in Belloni, T. (ed.): The Jet Paradigm
- From Microquasars to Quasars, Lect. Notes Phys. 794 (2009
Optical Identification of ROSAT sources in M 67: activity in an old cluster
We present optical identification and high-resolution spectroscopy of ROSAT
sources in the field of the old open cluster M 67. For the first time it is
possible to analyze coronal and chromospheric activity of active stars in a
solar-age cluster, and to compare it with field stars. ROSAT observed the high
X-ray luminosity tail of the cluster sources. In agreement with what expected
from studies of field stars, most of the detected X-ray sources are binaries,
preferably with short periods and eccentric orbits. In addition, several of the
M 67 ROSAT sources have peculiar locations in the cluster colour-magnitude
diagram. This is most likely due to rather complex evolutionary histories,
involving the presence of mass transfer or large mass losses. The X-ray
luminosity of the sources does not scale with the stellar parameters in an
obvious way. In particular, no relationship is found between coronal emission
and stellar magnitude or binary period. The Ca II K chromospheric flux from
most of the counterparts is in excess to that of single stars in the cluster by
one order of magnitude. The X-ray luminosity of the sources in the old M 67 is
one order of magnitude lower than the most active active binaries in the field,
but comparable to that of the much younger binaries in the Hyades.Comment: 11 pages, 6 figures. Accepted for publication by Astronomy &
Astrophysic
On the outburst evolution of H1743-322: a 2008/2009 comparison
We present two observational campaigns performed with the RXTE satellite on
the black hole transient H 1743-322. The source was observed in outburst on two
separate occasions between October-November 2008 and May-July 2009. We have
carried out timing and spectral analysis of the data set, obtaining a complete
state classification of all the observations. We find that all the observations
are well described by using a spectral model consisting of a disk-blackbody, a
powerlaw + reflection + absorption and a gaussian emission component. During
the 2009 outburst the system followed the canonical evolution through all the
states seen in black hole transients. In the 2008 outburst only the hard states
were reached. The early evolution of the spectral parameters is consistent
between the two epochs, and it does not provide clues about the subsequent
behavior of the source. The variation of the flux associated to the two main
spectral components (i.e. disk and powerlaw) allows us to set a lower limit to
the orbital inclination of the system of >= 43{\deg}.Comment: 13 pages, 5 figures. Accepted for publication in MNRA
Fast variability as a tracer of accretion regimes in black hole transients
We present the rms-intensity diagram for black hole transients. Using
observations taken with the Rossi X-ray timing explorer we study the relation
between the root mean square (rms) amplitude of the variability and the net
count-rate during the 2002, 2004 and 2007 outbursts of the black hole X-ray
binary GX 339-4. We find that the rms-flux relation previously observed during
the hard state in X-ray binaries does not hold for the other states, when
different relations apply. These relations can be used as a good tracer of the
different accretion regimes. We identify the hard, soft and intermediate states
in the rms-intensity diagram. Transitions between the different states are seen
to produce marked changes in the rms-flux relation. We find that one single
component is required to explain the ~ 40 per cent variability observed at low
count rates, whereas no or very low variability is associated to the
accretion-disc thermal component.Comment: Accepted for publication in MNRAS. 6 pages, 4 figure
X-ray emission from the PSR B1259--63 system near apastron
The PSR B1259--63 system contains a 47 ms radio pulsar in a highly eccentric
binary with a Be-star companion. Strongly time variable X-ray emission was
reported from this system as the pulsar was near apastron in 1992-early 1993.
The variability was primarily deduced from an apparent non-detection of the
\psr system during a first pre-apastron \ros observation in February~1992. We
have re-analyzed the \ros observations of the \psr system. Contrary to the
results of a previous analysis, we find that the \psr system was detected by
\ros during the first off-axis February~1992 observation. The intensity of the
soft X-ray emission of the \psr system before and after the 1992 apastron
appears to vary at most by a factor . Our results sensibly constrain
theoretical models of X-ray emission from the \psr system.Comment: LATEX, Accepted for publ. in ApJ
On the kHz QPO frequency correlations in bright neutron star X-ray binaries
We re-examine the correlation between the frequencies of upper and lower kHz
quasi-periodic oscillations (QPO) in bright neutron-star low-mass X-ray
binaries. By including the kHz QPO frequencies of the X-ray binary Cir X-1 and
two accreting millisecond pulsars in our sample, we show that the full sample
does not support the class of theoretical models based on a single resonance,
while models based on relativistic precession or Alfven waves describe the data
better. Moreover, we show that the fact that all sources follow roughly the
same correlation over a finite frequency range creates a correlation between
the linear parameters of the fits to any sub-sample.Comment: Accepted for publication in MNRAS; 7 pages, 4 figure
Low Luminosity States of the Black Hole Candidate GX~339--4. II. Timing Analysis
Here we present timing analysis of a set of eight Rossi X-ray Timing Explorer
(RXTE) observations of the black hole candidate GX 339-4 that were taken during
its hard/low state. On long time scales, the RXTE All Sky Monitor data reveal
evidence of a 240 day periodicity, comparable to timescales expected from
warped, precessing accretion disks. On short timescales all observations save
one show evidence of a persistent f approximately equal to 0.3 Hz QPO. The
broad band (10^{-3}-10^2 Hz) power appears to be dominated by two independent
processes that can be modeled as very broad Lorentzians with Q approximately
less than 1. The coherence function between soft and hard photon variability
shows that if these are truly independent processes, then they are individually
coherent, but they are incoherent with one another. This is evidenced by the
fact that the coherence function between the hard and soft variability is near
unity between 0.005-10 Hz but shows evidence of a dip at f approximately equal
to 1 Hz. This is the region of overlap between the broad Lorentzian fits to the
PSD. Similar to Cyg X-1, the coherence also drops dramatically at frequencies
approximately greater than 10 Hz. Also similar to Cyg X-1, the hard photon
variability is seen to lag the soft photon variability with the lag time
increasing with decreasing Fourier frequency. The magnitude of this time lag
appears to be positively correlated with the flux of GX 339-4. We discuss all
of these observations in light of current theoretical models of both black hole
spectra and temporal variability.Comment: To Appear in the AStrophysical Journa
X rays from old open clusters: M 67 and NGC 188
We have observed the old open clusters M 67 and NGC 188 with the ROSAT PSPC.
In M 67 we detect a variety of X-ray sources. The X-ray emission by a
cataclysmic variable, a single hot white dwarf, two contact binaries, and some
RS CVn systems is as expected. The X-ray emission by two binaries located below
the subgiant branch in the Hertzsprung Russell diagram of the cluster, by a
circular binary with a cool white dwarf, and by two eccentric binaries with
orbital period > 700 d is puzzling. Two members of NGC 188 are detected,
including the FK Com type star D719. Another possible FK Com type star,
probably not a member of NGC 188, is also detected.Comment: 10 pages, 5 figures. Accepted for publication on Astronomy &
Astrophysic
High-Frequency Quasi-Periodic Oscillations from GRS 1915+105
We report the results of a systematic timing analysis of all archival Rossi
X-Ray Timing Explorer (RXTE) observations of the bright black-hole binary GRS
1915+105 in order to detect high-frequency quasi-periodic oscillations (HFQPO).
We produced power-density spectra in two energy bands and limited the analysis
to the frequency range 30-1000 Hz. We found 51 peaks with a single trial
significance larger than 3 sigma. As all but three have centroid frequencies
that are distributed between 63 and 71 Hz, we consider most of them significant
regardless of the number of trials involved. The average centroid frequency and
FWHM are 67.3 +/- 2.0 Hz and 4.4 +/- 2.4 Hz respectively. Their fractional rms
varies between 0.4% and 2% (total band detections) and between 0.5% and 3%
(hard ban detections). As GRS 1915+105 shows large variability on time scales
longer than 1s, we analysed the data in 16s intervals and found that the
detections are limited to a specific region in the colour-colour diagram,
corresponding to state B of the source, when the energy spectrum is dominated
by a bright accretion disk component. However, the rms spectrum of the HFQPO is
very hard and does not show a flattening up to 40 keV, where the fractional rms
reaches 11%. We discuss our findings in terms of current proposed models and
compare them with the results on other black-hole binaries and neutron-star
binaries.Comment: 9 pages, 6 figures, Accepted for publication in MNRA
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