13 research outputs found
Evolution of AQL X-1 During the Rising Phase of its 1998 Outburst
We present results from 16 snapshots of Aql X-1 with RXTE during the rising
phase of its recent outburst. The observations were carried out at a typical
rate of once or twice per day. The source shows interesting spectral evolution
during this period. Phenomenologically, it bears remarkable similarities to
``atoll'' sources. Shortly after the onset of the outburst, the source is seen
to be in an ``island'' state, but with little X-ray variability. It then
appears to have made a rapid spectral transition (on a time scale less than
half a day) to another ``island'' state, where it evolves slightly and stays
for 4 days. In this state, the observed X-ray flux becomes increasingly
variable as the source brightens. Quasi-period oscillation (QPO) in the X-ray
intensity is detected in the frequency range 670--870 Hz. The QPO frequency
increases with the X-ray flux while its fractional rms decreases. The QPO
becomes undetectable following a transition to a ``banana'' state, where the
source continues its evolution by moving up and down the ``banana'' branch in
the color-color diagram as the flux (presumably, the mass accretion rate)
fluctuates around the peak of the outburst. Throughout the entire period, the
power density spectrum is dominated by very-low frequency noises. Little power
can be seen above ~1 Hz, which is different from typical ``atoll'' sources. In
the ``banana'' state, the overall X-ray variability remains low (with
fractional rms ~3--4%) but roughly constant. The observed X-ray spectrum is
soft with few photons from above 25 keV, implying the thermal origin of
the emission. The evolution of both spectral and temporal X-ray properties is
discussed in the context of disk-instability models.Comment: 13 pages, including one table and five figures. To appear in ApJ
Letters (July 20
The Hot and Energetic Universe: End points of stellar evolution
White dwarfs, neutron stars and stellar mass black holes are key laboratories
to study matter in most extreme conditions of gravity and magnetic field. The
unprecedented effective area of Athena+ will allow us to advance our
understanding of emission mechanisms and accretion physics over a wide range of
mass accretion rates, starting from lower and sub-luminous quiescent X-ray
binaries up to super-Eddington ultra-luminous sources. Athena+ will measure
stellar black hole spins in a much higher number of binaries than achievable
now, opening the possibility to study how spin varies with black hole history.
The high throughput and energy resolution of the X-IFU will be instrumental in
establishing how disc wind properties depend on accretion state, in determining
wind launching mechanism and in quantifying the impact of the wind induced mass
loss on binary evolution and environment. Triggers and high quality optical and
radio data originating from large wide field contemporaneous instruments will
provide essential complementary information on jet launching mechanisms and on
the physics of rotation powered pulsars, for instance. In addition, Athena+
will furnish multiple, independent measurements of the neutron star mass/radius
relation in a wide range of environments and conditions so as to constrain the
debated equation of state.Comment: Supporting paper for the science theme "The Hot and Energetic
Universe" to be implemented by the Athena+ X-ray observatory
(http://www.the-athena-x-ray-observatory.eu). 9 pages, 4 figure
Etude de la variabilité des binaires X de faible masse à partir d'observations avec RXTE
TOULOUSE3-BU Sciences (315552104) / SudocMEUDON-Observatoire (920482302) / SudocSudocFranceF
The Hot and Energetic Universe: A White Paper presenting the science theme motivating the Athena+ mission
This White Paper, submitted to the recent ESA call for science themes to define its future large missions, advocates the need for a transformational leap in our understanding of two key questions in astrophysics: 1) How does ordinary matter assemble into the large scale structures that we see today? 2) How do black holes grow and shape the Universe? Hot gas in clusters, groups and the intergalactic medium dominates the baryonic content of the local Universe. To understand the astrophysical processes responsible for the formation and assembly of these large structures, it is necessary to measure their physical properties and evolution. This requires spatially resolved X-ray spectroscopy with a factor 10 increase in both telescope throughput and spatial resolving power compared to currently planned facilities. Feedback from supermassive black holes is an essential ingredient in this process and in most galaxy evolution models, but it is not well understood. X-ray observations can uniquely reveal the mechanisms launching winds close to black holes and determine the coupling of the energy and matter flows on larger scales. Due to the effects of feedback, a complete understanding of galaxy evolution requires knowledge of the obscured growth of supermassive black holes through cosmic time, out to the redshifts where the first galaxies form. X-ray emission is the most reliable way to reveal accreting black holes, but deep survey speed must improve by a factor ~100 over current facilities to perform a full census into the early Universe. The Advanced Telescope for High Energy Astrophysics (Athena+) mission provides the necessary performance (e.g. angular resolution, spectral resolution, survey grasp) to address these questions and revolutionize our understanding of the Hot and Energetic Universe. These capabilities will also provide a powerful observatory to be used in all areas of astrophysics
The Hot and Energetic Universe: A White Paper presenting the science theme motivating the Athena+ mission
This White Paper, submitted to the recent ESA call for science themes to define its future large missions, advocates the need for a transformational leap in our understanding of two key questions in astrophysics: 1) How does ordinary matter assemble into the large scale structures that we see today? 2) How do black holes grow and shape the Universe? Hot gas in clusters, groups and the intergalactic medium dominates the baryonic content of the local Universe. To understand the astrophysical processes responsible for the formation and assembly of these large structures, it is necessary to measure their physical properties and evolution. This requires spatially resolved X-ray spectroscopy with a factor 10 increase in both telescope throughput and spatial resolving power compared to currently planned facilities. Feedback from supermassive black holes is an essential ingredient in this process and in most galaxy evolution models, but it is not well understood. X-ray observations can uniquely reveal the mechanisms launching winds close to black holes and determine the coupling of the energy and matter flows on larger scales. Due to the effects of feedback, a complete understanding of galaxy evolution requires knowledge of the obscured growth of supermassive black holes through cosmic time, out to the redshifts where the first galaxies form. X-ray emission is the most reliable way to reveal accreting black holes, but deep survey speed must improve by a factor ~100 over current facilities to perform a full census into the early Universe. The Advanced Telescope for High Energy Astrophysics (Athena+) mission provides the necessary performance (e.g. angular resolution, spectral resolution, survey grasp) to address these questions and revolutionize our understanding of the Hot and Energetic Universe. These capabilities will also provide a powerful observatory to be used in all areas of astrophysics