266 research outputs found
The effect of dust scattering on the timing properties of black holes
It has been known that sources with high absorption column density also have high dust column density along the line of sight. The differential delays caused by small angle scattering of X rays by dust may have important effects on the power spectra of Galactic black holes at low energies, and impact studies that use the relation between the rms amplitude of variability and energy to determine the origin of QPOs from these sources. We observed the high absorption column density (NH ˜1023 cm-2 ) GBH 1E1740.7-2942 for 20 ks simultaneously with XMM-Newton and RXTE. By comparing the power spectra from the events in the core of the point spread function (PSF) of XMM-Newton EPIC-PN (using imaging and excluding the scattering halo) and the RXTE data, we quantified the effects of small angle scattering on the timing properties of this source. The rms amplitude of variability in ˜2-6 keV band obtained from the XMM-Newton data is higher than that of the RXTE as expected from the a scattering halo contribution in the RXTE
State transitions and jet formation in black hole binaries
The daily monitoring observations of black hole transients with RXTE provided important clues on the conditions of the state transitions, both in terms of spectra and timing. The recent addition of monitoring in the optical-infrared and the radio band significantly extended our knowledge of the relation between the jets and the spectral states. However, there are still very important unanswered questions, most importantly, whether the formation of the jet triggers any change in the spectral and temporal properties of the source. The answer to this question is also intrinsically related to the origin of the hard X-ray emission. In this work, the relation between the jet and the state transitions is discussed, using the data from GX 339-4, 4U 1543-47, H 1743-322, and GRO J1655-40, concentrating on the evolution of spectral and temporal parameters before, during and after the formation of the jet
Temporal Variations of Strength and Location of the South Atlantic Anomaly as Measured by RXTE
The evolution of the particle background at an altitude of ~540 km during the
time interval between 1996 and 2007 is studied using the particle monitor of
the High Energy X-ray Timing Experiment on board NASA's Rossi X-ray Timing
Explorer. A special emphasis of this study is the location and strength of the
South Atlantic Anomaly (SAA). The size and strength of the SAA are
anti-correlated with the the 10.7 cm radio flux of the Sun, which leads the SAA
strength by ~1 year reflecting variations in solar heating of the upper
atmosphere. The location of the SAA is also found to drift westwards with an
average drift rate of about 0.3 deg/yr following the drift of the geomagnetic
field configuration. Superimposed to this drift rate are irregularities, where
the SAA suddenly moves eastwards and where furthermore the speed of the drift
changes. The most prominent of these irregularities is found in the second
quarter of 2003 and another event took place in 1999. We suggest that these
events are previously unrecognized manifestations of the geomagnetic jerks of
the Earth's magnetic field.Comment: 21 pages, 11 figures, accepted for publication in Earth and Planetary
Science Letter
A Clumpy Stellar Wind and Luminosity-Dependent Cyclotron Line Revealed by The First Suzaku Observation of the High-Mass X-ray Binary 4U 1538-522
We present results from the first Suzaku observation of the high-mass X-ray
binary 4U 1538-522. The broad-band spectral coverage of Suzaku allows for a
detailed spectral analysis, characterizing the cyclotron resonance scattering
feature at keV and the iron K line at
keV, as well as placing limits on the strengths of the iron K line and
the iron K edge. We track the evolution of the spectral parameters both in time
and in luminosity, notably finding a significant positive correlation between
cyclotron line energy and luminosity. A dip and spike in the lightcurve is
shown to be associated with an order-of-magnitude increase in column density
along the line of sight, as well as significant variation in the underlying
continuum, implying the accretion of a overdense region of a clumpy stellar
wind. We also present a phase-resolved analysis, with most spectral parameters
of interest showing significant variation with phase. Notably, both the
cyclotron line energy and the iron K line intensity vary significantly
with phase, with the iron line intensity significantly out-of-phase with the
pulse profile. We discuss the implications of these findings in the context of
recent work in the areas of accretion column physics and cyclotron resonance
scattering feature formation.Comment: 15 pages, 8 figures. Accepted to ApJ on 2 July 201
Twelve and a Half Years of Observations of Centaurus A with RXTE
The Rossi X-ray Timing Explorer has observed the nearest radio galaxy,
Centaurus A, in 13 intervals from 1966 August to 2009 February over the 3--200
keV band. Spectra accumulated over the 13 intervals were well described with an
absorbed power law and iron line. Cut-off power laws and Compton reflection
from cold matter did not provide a better description. For the 2009 January
observation, we set a lower limit on the cut-off energy at over 2 MeV. The
power spectral density function was generated from RXTE/ASM and PCA data, as
well as an XMM-Newton long look, and clear evidence for a break at 18+10-7 days
(68% conf.) was seen. Given Cen A's high black hole mass and very low value of
Lx/LEdd, the break was a factor of 17+/-9 times higher than the break frequency
predicted by the McHardy and co-workers' relation, which was empirically
derived for a sample of objects, which are radio-quiet and accreting at
relatively high values of Lbol/LEdd. We have interpreted our observations in
the context of a clumpy molecular torus. The variability characteristics and
the broadband spectral energy distribution, when compared to Seyferts, imply
that the bright hard X-ray continuum emission may originate at the base of the
jet, yet from behind the absorbing line of sight material, in contrast to what
is commonly observed from blazars.Comment: 56 pages, 12 figures, 4 tables, revised manuscript submitted to The
Astrophysical Journa
Evidence for different accretion regimes in GRO J1008-57
We present a comprehensive spectral analysis of the BeXRB GRO J1008-57 over a
luminosity range of three orders of magnitude using NuSTAR, Suzaku and RXTE
data. We find significant evolution of the spectral parameters with luminosity.
In particular the photon index hardens with increasing luminosity at
intermediate luminosities between erg s. This
evolution is stable and repeatedly observed over different outbursts. However,
at the extreme ends of the observed luminosity range, we find that the
correlation breaks down, with a significance level of at least . We
conclude that these changes indicate transitions to different accretion
regimes, which are characterized by different deceleration processes, such as
Coulomb or radiation breaking. We compare our observed luminosity levels of
these transitions to theoretical predications and discuss the variation of
those theoretical luminosity values with fundamental neutron star parameters.
Finally, we present detailed spectroscopy of the unique "triple peaked"
outburst in 2014/15 which does not fit in the general parameter evolution with
luminosity. The pulse profile on the other hand is consistent with what is
expected at this luminosity level, arguing against a change in accretion
geometry. In summary, GRO J1008-57 is an ideal target to study different
accretion regimes due to the well constrained evolution of its broad-band
spectral continuum over several orders of magnitude in luminosity.Comment: 13 pages, 7 figures, 3 tables. Accepted for publication in A&
Periodic Thermonuclear X-ray Bursts from GS 1826-24 and the Fuel Composition as a Function of Accretion Rate
We analyze 24 type I X-ray bursts from GS 1826-24 observed by the Rossi X-ray
Timing Explorer between 1997 November and 2002 July. The bursts observed
between 1997-98 were consistent with a stable recurrence time of 5.74 +/- 0.13
hr. The persistent intensity of GS 1826-24 increased by 36% between 1997-2000,
by which time the burst interval had decreased to 4.10 +/- 0.08 hr. In 2002
July the recurrence time was shorter again, at 3.56 +/- 0.03 hr. The bursts
within each epoch had remarkably identical lightcurves over the full approx.
150 s burst duration; both the initial decay timescale from the peak, and the
burst fluence, increased slightly with the rise in persistent flux. The
decrease in the burst recurrence time was proportional to Mdot^(-1.05+/-0.02)
(where Mdot is assumed to be linearly proportional to the X-ray flux), so that
the ratio alpha between the integrated persistent and burst fluxes was
inversely correlated with Mdot. The average value of alpha was 41.7 +/- 1.6.
Both the alpha value, and the long burst durations indicate that the hydrogen
is burning during the burst via the rapid-proton (rp) process. The variation in
alpha with Mdot implies that hydrogen is burning stably between bursts,
requiring solar metallicity (Z ~ 0.02) in the accreted layer. We show that
solar metallicity ignition models naturally reproduce the observed burst
energies, but do not match the observed variations in recurrence time and burst
fluence. Low metallicity models (Z ~ 0.001) reproduce the observed trends in
recurrence time and fluence, but are ruled out by the variation in alpha. We
discuss possible explanations, including extra heating between bursts, or that
the fraction of the neutron star covered by the accreted fuel increases with
Mdot.Comment: 9 pages, 6 figures, accepted by ApJ. Minor revisions following the
referee's repor
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