1,747 research outputs found
X-ray spectral state evolution in IGR J17091-3624 and comparison of its heartbeat oscillation properties with those of GRS 1915+105
In this work, we study the X-ray timing and spectral evolution of the
transient low mass X-ray binary IGR J17091-3624 during first 66 days of its
2011 outburst. We present results obtained from observations with two
instruments, Rossi X-ray Timing Explorer (RXTE)/Proportional Counter Array
(PCA) and SWIFT/X-ray telescope (XRT), between 09 February, 2011 and 15 April,
2011. Using quasi-periodic oscillation classifications, power density spectrum
characteristics, time-lag behavior and energy spectral properties, we determine
source states and their transitions at different times of the outburst. During
the first part of the evolution, the source followed trends usually observed
from transient black hole X-ray binaries (BHXBs). Interestingly, a gradual
transition is observed in IGR J17091-3624 from the low-variability SIMS,
commonly seen in BHXBs, to a high-variability state with regular, repetitive
and structured pulsations, seen only from GRS 1915+105 (also known as 'rho'
class variability/'heartbeat' oscillations). We study the time evolution of
characteristic time-scale, quality factor and rms amplitude of heartbeat
oscillations in IGR J17091-3624. We also present a detailed comparison of the
timing and spectral properties of heartbeat oscillations and their evolution in
IGR J17091-3624 and GRS 1915+105.Comment: 23 pages, 10 figures, 3 tables, accepted for publication in the Ap
Fluctons
From the perspective of topological field theory we explore the physics
beyond instantons. We propose the fluctons as nonperturbative topological
fluctuations of vacuum, from which the self-dual domain of instantons is
attained as a particular case. Invoking the Atiyah-Singer index theorem, we
determine the dimension of the corresponding flucton moduli space, which gives
the number of degrees of freedom of the fluctons. An important consequence of
these results is that the topological phases of vacuum in non-Abelian gauge
theories are not necessarily associated with self-dual fields, but only with
smooth fields. Fluctons in different scenarios are considered, the basic
aspects of the quantum mechanical amplitude for fluctons are discussed, and the
case of gravity is discussed briefly
Forward Flux Sampling for rare event simulations
Rare events are ubiquitous in many different fields, yet they are notoriously
difficult to simulate because few, if any, events are observed in a conventiona
l simulation run. Over the past several decades, specialised simulation methods
have been developed to overcome this problem. We review one recently-developed
class of such methods, known as Forward Flux Sampling. Forward Flux Sampling
uses a series of interfaces between the initial and final states to calculate
rate constants and generate transition paths, for rare events in equilibrium or
nonequilibrium systems with stochastic dynamics. This review draws together a
number of recent advances, summarizes several applications of the method and
highlights challenges that remain to be overcome.Comment: minor typos in the manuscript. J.Phys.:Condensed Matter (accepted for
publication
Low-frequency QPO from the 11 Hz accreting pulsar in Terzan 5: not frame dragging
We report on 6 RXTE observations taken during the 2010 outburst of the 11 Hz
accreting pulsar IGR J17480-2446 located in the globular cluster Terzan 5.
During these observations we find power spectra which resemble those seen in
Z-type high-luminosity neutron star low-mass X-ray binaries, with a
quasi-periodic oscillation (QPO) in the 35-50 Hz range simultaneous with a kHz
QPO and broad band noise. Using well known frequency-frequency correlations, we
identify the 35-50 Hz QPOs as the horizontal branch oscillations (HBO), which
were previously suggested to be due to Lense-Thirring precession. As IGR
J17480-2446 spins more than an order of magnitude more slowly than any of the
other neutron stars where these QPOs were found, this QPO can not be explained
by frame dragging. By extension, this casts doubt on the Lense-Thirring
precession model for other low-frequency QPOs in neutron-star and perhaps even
black-hole systems.Comment: 6 pages, 5 figures, Accepted for publication in ApJ
An X-ray view of the very faint black hole X-ray transient Swift J1357.2-0933 during its 2011 outburst
We report on the X-ray spectral (using XMM-Newton data) and timing behavior
(using XMM-Newton and Rossi X-ray Timing Explorer [RXTE] data) of the very
faint X-ray transient and black hole system Swift J1357.2-0933 during its 2011
outburst. The XMM-Newton X-ray spectrum of this source can be adequately fitted
with a soft thermal component with a temperature of ~0.22 keV (using a disc
model) and a hard, non-thermal component with a photon index of ~1.6 when using
a simple power-law model. In addition, an edge at ~ 0.73 keV is needed likely
due to interstellar absorption. During the first RXTE observation we find a 6
mHz quasi-periodic oscillation (QPO) which is not present during any of the
later RXTE observations or during the XMM-Newton observation which was taken 3
days after the first RXTE observation. The nature of this QPO is not clear but
it could be related to a similar QPO seen in the black hole system H 1743-322
and to the so-called 1 Hz QPO seen in the dipping neutron-star X-ray binaries
(although this later identification is quite speculative). The observed QPO has
similar frequencies as the optical dips seen previously in this source during
its 2011 outburst but we cannot conclusively determine that they are due to the
same underlying physical mechanism. Besides the QPO, we detect strong
band-limited noise in the power-density spectra of the source (as calculated
from both the RXTE and the XMM-Newton data) with characteristic frequencies and
strengths very similar to other black hole X-ray transients when they are at
low X-ray luminosities. We discuss the spectral and timing properties of the
source in the context of the proposed very high inclination of this source. We
conclude that all the phenomena seen from the source cannot, as yet, be
straightforwardly explained neither by an edge-on configuration nor by any
other inclination configuration of the orbit.Comment: 9 pages, 4 figures, 1 table. Accepted for publication in MNRA
The identification of MAXI J1659-152 as a black hole candidate
We report on the analysis of all 65 pointed Rossi X-ray Timing Explorer
observations of the recently discovered soft X-ray transient MAXI J1659-152
(initially referred to as GRB 100925A). The source was studied in terms of its
evolution through the hardness-intensity diagram (HID) as well as its X-ray
variability properties. MAXI J1659-152 traced out an anti-clockwise loop in the
HID, which is commonly seen in transient low-mass X-ray binaries. The
variability properties of the source, in particular the detection of type-B and
type-C low-frequency quasi-periodic oscillations, and the way they evolve along
the HID track, indicate that MAXI J1659-152 is a black hole candidate. The
spectral and variability properties of MAXI J1659-152 imply that the source was
observed in the hard and soft intermediate states during the RXTE observations,
with several transitions between these two states.Comment: 6 pages, 4 figures, accepted for publication in ApJ
Thermal performance and comfort of naturally ventilated earth housing in dry-summer climate
This paper presents a study of the thermal performance and occupant satisfaction of naturally
ventilated earth houses during a hot summer period. An earth house community located in Santiago, Chile, was
chosen as a case study. Building Use Studies (BUS) survey was used to understand the general satisfaction and
thermal comfort of users living in earth buildings. In parallel, two occupied houses constructed with wattle and
daub techniques were monitored. Occupants highly rated most aspect of the house, yet thermal related
variables are less satisfactory. The monitored results showed that indoor diurnal temperatures in both houses
have differences between 15-20°C compared with outdoor temperatures. The indoor temperature of adobe
bedroom showed a more drastic deviation when the outdoor temperature was lower than 20°C. This study has
verified the thermal comfort potential of earthen constructions, notably contributing to indoor temperatures in
summer
- …