847 research outputs found
Low frequency QPOs and possible change in the accretion geometry during the outbursts of Aquila X1
We have studied the evolution of the Low Frequency Quasi-Periodic
Oscillations (LFQPOs) during the rising phase of seven outbursts of the neutron
star Soft X-ray Transient (SXT) Aql X1 observed with the \textit{Rossi X-ray
Timing Explorer (RXTE)}. The frequency correlation between the low frequency
break and the LFQPO sampled on the time scale of 2 days was seen. Except
for the peculiar 2001 outburst, the frequency of the LFQPOs increased with time
before the hard-to-soft state transition up to a maximum at
31 Hz, a factor of 5 higher than those seen in black hole
transients such as GX 3394, making the maximum QPO frequency a likely
indicator of the mass of the central compact object. The characteristic
frequencies increased by around ten percent per day in the early rising phase
and accelerated to nearly one hundred percent per day since 2 days before
the hard-to-soft state transition. We examined the dependence of the frequency
on the source flux and found an anti-correlation between the
maximum frequency of the LFQPOs and the corresponding X-ray luminosity of the
hard-to-soft transition (or outburst peak luminosity) among the outbursts. We
suggest that X-ray evaporation process can not be the only mechanism that
drives the variation of the inner disk radius if either of the twin kHz QPO
corresponds to the Keplerian frequency at the truncation radius.Comment: 8 pages, 8 figures, 1 table; accepted for publication in Ap
Energy dependent power spectral states and origin of aperiodic variability in black hole binaries
We found the black hole candidate MAXI J1659-152 showed distinct power
spectra, i.e., a power-law noise (PLN) vs. band-limited noise (BLN) plus
quasi-periodic oscillations (QPOs), below and above about 2 keV respectively,
in the observations with the Swift and the RXTE during the 2010 outburst,
indicating a high energy cut-off of the PLN and a low energy cut-off of the BLN
and the QPOs around 2 keV. The emergence of the PLN and the fading of the BLN
and the QPOs initially took place from below 2 keV when the source entered the
hard intermediate state and finally settled in the soft state three weeks
later. The evolution was accompanied by the emergence of the disk spectral
component and decreases in the amplitudes of variability in the soft X-ray and
the hard X-ray bands. Our results indicate that the PLN is associated with the
optically thick disk in both hard and intermediate states, and power spectral
state is independent of the X-ray energy spectral state in a broadband view. We
suggest that in the hard and the intermediate state, the BLN and the QPOs
emerge from the innermost hot flow subjected to Comptonization, while the PLN
originates from the optically thick disk further out. The energy cut-offs of
the PLN and the BLN or QPOs then follow the temperature of the seed photons
from the inner edge of the optically thick disk, while the high frequency
cut-off of the PLN follows the orbital frequency at the inner edge of the
optically thick disk as well.Comment: 5 pages, 6 figures, accepted for publication in Ap
Cyclic best first search in branch-and-bound algorithms
In this dissertation, we study the application of a search strategy called cyclic best first search (CBFS) in branch-and-bound (B&B) algorithms. First, we solve a one machine scheduling problem with release and delivery times with the minimum makespan objective with a B&B algorithm using a variant of CBFS called CBFS-depth and a modified heuristic for finding feasible schedules. Second, we investigate the conditions of the search trees that may lead to CBFS-depth outperforming BFS in terms of the average number of nodes explored to prove optimality. Finally, we present a B&B algorithm using CBFS for a close-enough traveling salesman problem that demonstrates the benefit of using CBFS even if it does not improve the number of nodes explored to prove optimality. Overall, we show that using CBFS has a number of advantages to the performance of a B&B algorithm in comparison to the other search strategies given the right problems
A comparative study on space configuration in Japanese and Chinese gardens : By analyzing visibility and permeability of Shoin-style gardens in Kyoto and private gardens in Suzhou
早稲田大学博士(建築学)早大学位記番号:新9513doctoral thesi
An apparent positive relation between spin and orbital angular momentum in X-ray binaries
The origin of current angular momentum (AM) of the black hole (BH) in X-ray
binary (XRB) is still unclear, which is related with the birth and/or the
growth of the BH. Here we collect the spin parameters measured in BH
XRBs and find an apparent bimodal distribution centered at 0.17 and
0.83. We find a positive relation between the spin parameter and the orbital
period/orbital separation through combining distinct XRB categories, including
neutron star (NS) low-mass X-ray binaries (LMXBs), Roche-lobe overflow (RLOF)
BH XRBs and wind-fed BH XRBs. It seems that the AM of the compact star and the
binary orbit correlates by combining the different XRB systems. These positive
relations imply that accretion process is a common mechanism for spinning up
the compact star in these diverse XRB systems. We infer that the low and high
spin BH XRBs may experience different evolution and accretion history, which
corresponds to the bimodal distribution of the BH spin parameters. The low spin
BHs () are similar to the NS LMXBs, the compact star of which is
spun-up by the low-level accretion, and the high spin BHs () had
experienced a short hypercritical accretion ()
period, during which, the BH spin dramatically increased.Comment: 13 pages, 7 figures, accepted for publication in MNRA
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