3,780 research outputs found
On the Relation of Hard X-ray Peak Flux and Outburst Waiting Time in the Black Hole Transient GX 339-4
Aims. In this work we re-investigated the empirical relation between the hard
X-ray peak flux and the outburst waiting time found previously in the black
hole transient GX 339-4. We tested the relation using the observed hard X-ray
peak flux of the 2007 outburst of GX 339-4, clarified issues about faint
flares, and estimated the lower limit of hard X-ray peak flux for the next
outburst. Methods. We included Swift/BAT data obtained in the past four years.
Together with the CGRO/BATSE and RXTE/HEXTE light curves, the observations used
in this work cover a period of 18 years. Results. The observation of the 2007
outburst confirms the empirical relation discovered before. This strengthens
the apparent link between the mass in the accretion disk and the peak
luminosity of the brightest hard state that the black hole transient can reach.
We also show that faint flares with peak fluxes smaller than about 0.12 crab do
not affect the empirical relation. We predict that the hard X-ray peak flux of
the next outburst should be larger than 0.65 crab, which will make it at least
the second brightest in the hard X-ray since 1991.Comment: 4 pages, 3 figures, accepted by A&
Ultrafast dephasing of coherent optical phonons in atomically controlled GeTe/SbTe superlattices
Femtosecond dynamics of coherent optical phonons in GeTe/SbTe
superlattices (SLs), a new class of semiconductor SLs with three different
states, have been investigated by using a reflection-type pump-probe technique
at various lattice temperatures. The time-resolved transient reflectivity (TR)
obtained in as-grown SLs exhibits the coherent A optical modes at 5.10
THz and 3.78 THz, while only the single A mode at 3.68 THz is observed in
annealed SLs. The decay rate of the A mode in annealed SLs is strongly
temperature dependent, while that in as-grown SLs is not temperature dependent.
This result indicates that the damping of the coherent A phonons in
amorphous SLs is governed by the phonon-defect (vacancy) scattering rather than
the anharmonic phonon-phonon coupling.Comment: 5 pages, 5 figure
The faint 2005 hard state outburst of Aquila X-1 seen by INTEGRAL and RXTE
We report on the spectral analysis of RXTE and INTEGRAL data of the 2005
April outburst of the transient Atoll source Aql X-1. Although this outburst is
one of the faintest ever detected for this source in the soft X-rays
(RXTE/ASM), one of our INTEGRAL observations, taken close to the soft X-ray
peak, shows that the source flux was quite high, with a 20-200 keV flux of 2.05
x 10^-9 erg cm^-2 s^-1. On this occasion we detect the source up to 150 keV for
the first time. We compare and discuss the similarity of the source behavior
with that of black hole transients especially XTE J1550-564.Comment: 4 pages 2 figures, Accepted for publication in A&A as a RESEARCH NOT
Ground state of graphite ribbons with zigzag edges
We study the interaction effects on the ground state of nanographite ribbons
with zigzag edges. Within the mean-field approximation, we found that there are
two possible phases: the superconducting (SC) phase and the excitonic insulator
(EI). The two phases are separated by a first-order transition point. After
taking into account the low-lying fluctuations around the mean-field solutions,
the SC phase becomes a spin liquid phase with one gapless charge mode.
On the other hand, all excitations in the EI phase, especially the spin
excitations, are gapped.Comment: 6 pages, 3 figure
The correlation timescale of the X-ray flux during the outbursts of soft X-ray transients
Recent studies of black hole and neutron star low mass X-ray binaries (LMXBs)
show a positive correlation between the X-ray flux at which the
low/hard(LH)-to-high/soft(HS) state transition occurs and the peak flux of the
following HS state. By analyzing the data from the All Sky Monitor (ASM)
onboard the Rossi X-ray Timing Explorer (RXTE), we show that the HS state flux
after the source reaches its HS flux peak still correlates with the transition
flux during soft X-ray transient (SXT) outbursts. By studying large outbursts
or flares of GX 339-4, Aql X-1 and 4U 1705-44, we have found that the
correlation holds up to 250, 40, and 50 d after the LH-to-HS state transition,
respectively. These time scales correspond to the viscous time scale in a
standard accretion disk around a stellar mass black hole or a neutron star at a
radius of ~104-5 Rg, indicating that the mass accretion rates in the accretion
flow either correlate over a large range of radii at a given time or correlate
over a long period of time at a given radius. If the accretion geometry is a
two-flow geometry composed of a sub-Keplerian inflow or outflow and a disk flow
in the LH state, the disk flow with a radius up to ~105 Rg would have
contributed to the nearly instantaneous non-thermal radiation directly or
indirectly, and therefore affects the time when the state transition occurs.Comment: 7 pages, 3 figure
CLINICAL PREDICTORS FOR ATHEROMA PROGRESSION DESPITE OPTIMAL GLYCEMIC CONTROL IN EARLY-STAGE DIABETIC PATIENTS: SUB-ANALYSIS FROM DIANA STUDY
Data de realització de les fotografies del Mercat aproximada (1994
Stochastic Heterostructures in B/N-Doped Carbon Nanotubes
Carbon nanotubes are one-dimensional and very narrow. These obvious facts
imply that under doping with boron and nitrogen, microscopic doping
inhomogeneity is much more important than for bulk semiconductors. We consider
the possibility of exploiting such fluctuations to create interesting devices.
Using self-consistent tight-binding (SCTB), we study heavily doped highly
compensated nanotubes, revealing the spontaneous formation of structures
resembling chains of random quantum dots, or nano-scale diode-like elements in
series. We also consider truly isolated impurities, revealing simple scaling
properties of bound state sizes and energies.Comment: 4 pages RevTeX, 4 PostScript figure
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