152 research outputs found
Spectral variability in Cygnus X-3
We model the broad-band X-ray spectrum of Cyg X-3 in all states displayed by
this source as observed by the Rossi X-ray Timing Explorer. From our models, we
derive for the first time unabsorbed spectral shapes and luminosities for the
full range of spectral states. We interpret the unabsorbed spectra in terms of
Comptonization by a hybrid electron distribution and strong Compton reflection.
We study the spectral evolution and compare with other black hole as well as
neutron star sources. We show that a neutron star accretor is not consistent
with the spectral evolution as a function of Ledd and especially not with the
transition to a hard state. Our results point to the compact object in Cyg X-3
being a massive, ~30 Msun black hole.Comment: 14 pages, 9 figures, accepted for publication in MNRA
Analysing the Suzaku Spectra of the Broad-Line Seyfert 1 Galaxy CBS 126
We analysed new simultaneous \emph{Suzaku} and \emph{Swift} data of the Broad
Line Seyfert 1 (BLS1) galaxy CBS 126. A clear Fe emission line and a strong
soft excess are present in the source spectra. We fit the spectra with a
relativistic reflection model and find the model tends to fit the data with a
high iron abundance possibly due to the large soft excess present. By checking
the difference and the RMS spectra, we find there is likely an absorption edge
at 0.89 keV, which might be caused by oxygen or neon. We also produced
an analysis of the time-resolved spectra in order to examine the existence of
the edge. Although high iron abundance is required more in the time-resolved
spectra, a model of solar iron abundance together with an absorption edge gives
a more physical explanation. Variation of the ionisation parameter is an
alternative, plausible explanation for the excess seen in the difference
spectra. It is difficult to know if there are warm absorbers in this source
from the current data. To further investigate the presence of possible warm
absorbers, higher signal-to-noise low-energy data are needed. The work
presented here tentatively suggests that the spectra of a BLS1 can be explained
by a relativistic reflection model similar to that often seen in their
narrow-line cousins.Comment: 10 pages, 12 figures, accepted for publication in MNRA
Disentangling jet and disc emission from the 2005 outburst of XTE J1118+480
The black hole X-ray transient, XTE J1118+480, has now twice been observed in
outburst - 2000 and 2005 - and on both occasions remained in the low/hard X-ray
spectral state. Here we present radio, infrared, optical, soft X-ray and hard
X-ray observations of the more recent outburst. We find that the lightcurves
have very different morphologies compared with the 2000 event and the optical
decay is delayed relative to the X-ray/radio. We attribute this lesser degree
of correlation to contributions of emission from multiple components, in
particular the jet and accretion disc. Whereas the jet seemed to dominate the
broadband spectrum in 2000, in 2005 the accretion disc seems to be more
prominent and we use an analysis of the lightcurves and spectra to distinguish
between the jet and disc emission. There also appears to be an optically thin
component to the radio emission in the 2005 data, possibly associated with
multiple ejection events and decaying as the outburst proceeds. These results
add to the discussion that the term "low/hard state'" covers a wider range of
properties than previously thought, if it is to account for XTE J1118+480
during these two outbursts.Comment: Accepted for publication in MNRA
Optical counterpart of HLX-1 during the 2010 outburst
We studied the optical counterpart of the intermediate-mass black hole
candidate HLX-1 in ESO 243-49. We used a set of Very Large Telescope imaging
observations from 2010 November, integrated by Swift X-ray data from the same
epoch. We measured standard Vega brightnesses U = 23.89 +/- 0.18 mag, B = 25.19
+/- 0.30 mag, V = 24.79 +/- 0.34 mag and R = 24.71 +/- 0.40 mag. Therefore, the
source was ~1 mag fainter in each band than in a set of Hubble Space Telescope
images taken a couple of months earlier, when the X-ray flux was a factor of 2
higher. We conclude that during the 2010 September observations, the optical
counterpart was dominated by emission from an irradiated disk (which responds
to the varying X-ray luminosity), rather than by a star cluster around the
black hole (which would not change). We modelled the Comptonized, irradiated
X-ray spectrum of the disk, and found that the optical luminosity and colours
in the 2010 November data are still consistent with emission from the
irradiated disk, with a characteristic outer radius r_{out} ~ 2800 r_{in} ~
10^{13} cm and a reprocessing fraction ~ 2 x 10^{-3}. The optical colours are
also consistent with a stellar population with age <~ 6 Myr (at solar
metallicity) and mass ~ 10^4 M_{sun}; this is only an upper limit to the mass,
if there is also a significant contribution from an irradiated disk. We
strongly rule out the presence of a young super-star-cluster, which would be
too bright. An old globular cluster might be associated with HLX-1, as long as
its mass <~ 2 x 10^6 M_{sun} for an age of 10 Gyr, but it cannot significantly
contribute to the observed very blue and variable optical/UV emission.Comment: Accepted by MNRAS on Nov 28; 11 pages, 1.3 MB. v2: same paper, same
price, now 20% more authors
X-ray reflection spectra from ionized slabs
X-ray reflection spectra are an important component in the X-ray spectra of
many active galactic nuclei and Galactic black hole candidates. It is likely
that reflection takes place from highly ionized surfaces of the accretion disc
in some cases. This can lead to strong Comptonization of the emergent iron, and
other, absorption and emission features. We present such reflection spectra
here, computed in a self-consistent manner with the method described by Ross
and Fabian. In particular we emphasise the range where the ionization parameter
(the flux to density ratio) \xi is around and above 10^4. Such spectra may be
relevant to the observed spectral features found in black hole candidates such
as Cygnus X-1 in the low/hard state.Comment: 7 pages with 5 postscript figures. Accepted for publication in MNRA
X-ray Reverberation close to the black hole in RE J1034+396
In previous work, we discussed the detection of reverberation delays in the
NLS1 1H0707-495. The delays originate close to the black hole. Here, we show
that RE J1034+396 shows very similar lag properties. At low frequencies (< 1
\times 10-4 Hz), the time lag between energy bands increases with energy
separation, similar to that commonly seen in Galactic black holes and other
AGN. At higher frequencies (~ 3.5 \times 10-4 Hz), the soft (< 1 keV) and hard
(> 3 keV) bands lag behind the intermediate band (1-3 keV). The simplest
interpretation is that the intermediate band is dominated by the direct
power-law continuum, while the soft and hard bands are dominated by the
relativistically-smeared reflected emission. The low frequency delays are
present in both available observations. The high frequency lags are only seen
in one observation. In the observation where high frequency reverberation
delays are observed, the spectrum contains a power-law component and there is a
QPO in the light curve. In the other observation, no power-law component is
required and no QPO is seen. The lags originate a few gravitational radii from
the black hole, and the QPO is associated with the power-law emitting corona.Comment: Accepted for publication in MNRA
The quasar PG 0844+349 in an X-ray weak state
In March 2009 the well-studied quasar, PG 0844+349, was discovered with Swift
to be in an X-ray weak state. A follow-up XMM-Newton observation several weeks
later generated a good quality spectrum of the source, showing substantial
curvature and spectral hardening. In combination with archival data at two
previous epochs when the source was in a bright state, we examine the long-term
spectral and timing properties of PG 0844+349 spanning nearly ten years and a
factor of ten in brightness. Partial covering and blurred reflection models are
compared to the data at each flux state while attempting to maintain
consistency between the various epochs. In terms of the blurred reflection
model, PG 0844+349 is in a reflection dominated state during the 2009 X-ray
weak observations, which can be understood in terms of light bending. Moreover,
the light bending scenario can also account for the short-term (i.e. ~1000s)
spectral variability in the source. Other models cannot be decisively ruled
out, but we note distinguishing features of the models that can be explored for
in higher signal-to-noise data from current and future observatories.Comment: 11 pages. Accepted for publication in MNRA
An additional soft X-ray component in the dim low/hard state of black hole binaries
We test the truncated disc models using multiwavelength (optical/UV/X-ray)
data from the 2005 hard state outburst of the black hole SWIFT J1753.5-0127.
This system is both fairly bright and has fairly low interstellar absorption,
so gives one of the best datasets to study the weak, cool disc emission in this
state. We fit these data using models of an X-ray illuminated disc to constrain
the inner disc radius throughout the outburst. Close to the peak, the observed
soft X-ray component is consistent with being produced by the inner disc, with
its intrinsic emission enhanced in temperature and luminosity by reprocessing
of hard X-ray illumination in an overlap region between the disc and corona.
This disc emission provides the seed photons for Compton scattering to produce
the hard X-ray spectrum, and these hard X-rays also illuminate the outer disc,
producing the optical emission by reprocessing.
However, the situation is very different as the outburst declines. The
optical is probably cyclo-synchrotron radiation, self-generated by the flow,
rather than tracing the outer disc. Similarly, limits from reprocessing make it
unlikely that the soft X-rays are directly tracing the inner disc radius. This
is seen more clearly in a similarly dim low/hard state spectrum from XTE
J1118+480. The very small emitting area implied by the relatively high
temperature soft X-ray component is completely inconsistent with the much
larger, cooler, UV component which is well fit by a truncated disc. We
speculate on the origin of this component, but its existence as a clearly
separate spectral component from the truncated disc in XTE J1118+480 shows that
it does not simply trace the inner disc radius, so cannot constrain the
truncated disc models.Comment: 11 pages, 10 figures, submitted to MNRA
Detectability of low energy X-ray spectral components in type 1 AGN
In this paper we examine the percentage of type 1 AGN which require the
inclusion of a soft excess component and/or significant cold absorption in the
modelling of their X-ray spectra obtained by XMM-Newton. We do this by
simulating spectra which mimic typical spectral shapes in order to find the
maximum detectability expected at different count levels. We then apply a
correction to the observed percentages found for the Scott et al. (2011) sample
of 761 sources. We estimate the true percentage of AGN with a soft excess
component to be 75+/-23%, suggesting that soft excesses are ubiquitous in the
X-ray spectra of type 1 AGN. By carrying out joint fits on groups of low count
spectra in narrow z bins in which additional spectral components were not
originally detected, we show that the soft excess feature is recovered with a
mean temperature kT and blackbody to power-law normalisation ratio consistent
with those of components detected in individual high count spectra. Cold
absorption with nH values broadly consistent with those reported in individual
spectra are also recovered. We suggest such intrinsic cold absorption is found
in a minimum of ~5% of type 1 AGN and may be present in up to ~10%.Comment: 10 pages, 6 figures, 4 tables. Accepted for publication in MNRA
States and transitions in black-hole binaries
With the availability of the large database of black-hole transients from the
Rossi X-Ray Timing Explorer, the observed phenomenology has become very
complex. The original classification of the properties of these systems in a
series of static states sorted by mass accretion rate proved not to be able to
encompass the new picture. I outline here a summary of the current situation
and show that a coherent picture emerges when simple properties such as X-ray
spectral hardness and fractional variability are considered. In particular,
fast transition in the properties of the fast time variability appear to be
crucial to describe the evolution of black-hole transients. Based on this
picture, I present a state-classification which takes into account the observed
transitions. I show that, in addition to transients systems, other black-hole
binaries and Active Galactic Nuclei can be interpreted within this framework.
The association between these states and the physics of the accretion flow
around black holes will be possible only through modeling of the full time
evolution of galactic transient systems.Comment: 30 pages, 11 figures, To appear in Belloni, T. (ed.): The Jet
Paradigm - From Microquasars to Quasars, Lect. Notes Phys. 794 (2009
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